Transportation Engineering-I

Transportation Engineering-I

With Lab Experiments in Detail




This note is prepared including six chapters as per the syllabus of IOE. First chapter describes about the transportation system and planning including the scenarios and history in Nepal. Second chapter deals about the road alignment survey. Road geometrical parameters and its design considerations with some solved and unsolved numerical examples are presented in chapter three. The drainage system and design considerations are described in chapter five. Special design considerations and special structures used in hill roads are described in chapter five. In last chapter, different road construction materials, their properties, different lab tests are described. Few solved and unsolved examples are also presented for combination of aggregate in this chapter.                                                        I am hereby express sincere acknowledgement to my professors, lecturers and colleagues.                                                                                                                                                      

BY:
Er. Bishnu Prasad Devkota

Lecturer in Himalaya College of Engineering
M. Sc. in Transportation Engineering
IOE, Pulchowk Campus

© All Right Reserved



July 22, 2013

 
TABLE OF CONTENTS

CH-1, INTRODUCTION TO TRANSPORTATION PLANNING & ENGINEERING 4
1.1 Transportation Engineering 4
Overview: 4
1.2 Modes of Transportation 4
1.3 Comparison between various modes of Transportation and their Relevance in Nepal 4
1.4 Historical Development & Construction of Highway in Nepal 8
1.5 Highway Planning 9
Objectives of Road/Highway Planning: 9
National Road Network Panning 10
Urban Road Network Planning 12
Ring Roads 13
1.6 Classification of Highway in Nepal 16
NRS Classification of Roads: 16
The five classes of Rural Transport Linkages (as per Nepal Rural Road Standard 2055): 17
CH-2, HIGHWAY ALIGNMENT AND ENGINEERING SURVEY 19
2.1 Highway alignment and controlling factors 19
2.2.1 Introduction: 19
2.1.2 Requirements of Highway Alignment: 19
2.1.3 Factors controlling road alignment 19
2.2 Highway survey 20
2.2.1 Structure of Route Location Process: 20
2.2.2 The stages of engineering survey are: 21
2.4 Class-Work on Alignment Selection 23
2.2 Identification of Road Project and Feasibility Study: 23
2.5 Components of an Economic Appraisal: 24
3.0 GEOMETRIC DESIGN 26
3.1 DEFINITION AND SCOPE: 26
3.2 CONTROLS AND CRITERIA FOR ROAD DESIGN 26
3.2.1 Factors which controls the geometric design: 26
3.2.2 Criteria for geometric design: 28
3.3 & 3.4 TYPICAL CROSS-SECTIONAL ELEMENTS: 28
3.4 ELEMENTS OF HORIZONTAL ALIGNMENT 33
3.4.2 Design of Horizontal Curves: 35
3.4.3 SIGHT DISTANCE 36
3.4.4  SUPERELEVATION 41
3.4.5 EXTRAWIDENING AT THE CURVED PATH 45
3.4.6 TRANSITION CURVE: Definition, Types and Design 47
3.5 ELEMENTS OF VERTICAL CURVE 49
3.5.1 Definition and Types of Gradient: 49
3.5.2 Momentum Grade 50
3.5.3 Grade Compensation 50
3.5.1 Definition and Types of Vertical Curve 50
3.5.2 Design of Vertical Summit Curve 50
3.5.3 Design of Vertical Valley Curve 51
3.5.4 Lowest point of Valley  Curve and Highest point of Summit Curve 51
4.0 HIGHWAY DRAINAGE SYSTEM 55
4.1 INTRODUCTION 55
4.1.1 Highway Drainage System: An Introduction 55
4.1.2 Highway Drainage System: Importance 56
4.2 Causes of Moisture Variation in Subgrade Soil: 56
4.3 Surface Drainage System: 59
4.3.1 Longitudinal drain: 59
4.3.2 Cross- Drainage Structure 62
4.3.3 Erosion control and Energy Dissipating Structures 65
4.4 Subsurface Drainage 67
4.4.1 Drainage of Infiltrated Water 67
4.4.2 Control of Seepage Flow 67
4.4.3 Lowering of Water Table 68
4.4.4 Control of Capillary rise 69
4.4.5 Procedures for Drainage Design 70
5.0 HILL ROADS 71
5.1 Introduction 71
5.2 Special Considerations in Hill Road Design 71
5.2.1 Alignment Selection in Hill Road 71
5.2.2 Geometric Design of Hill Road 73
Design and Types of Hair Pin Bends: 75
5.2.3 Different types of Hill Road Cross-Sections: 77
5.3 Special Structures in Hill Roads 81
6.0 HIGHWAY MATERIALS 85
6.1 Introduction and Classification of highway materials 85
6.2 Sub-Grade Soil 85
6.2.2 Characteristics of sub grade soil 86
6.2.3 Desirable Properties of soil as a Highway construction material 86
6.3 Road Aggregates 86
6.3.1 Definition, Classification of Road Aggregates 86
6.3.2 Desirable Properties of Road Aggregates 87
6.3.3 Tests on Aggregates and their significance 87
6.3.4 Comparing Gradation Specification and Method of Translating Specification 93
6.3.5 Combination of Aggregates: 94
6.4 BITUMINOUS ROAD BINDERS 101
6.4.1 Definition and Classification of Road Binders 101
6.4.2 Liquid Bitumen: Cutback bitumen and Bitumen Emulsion 102
6.4.3 Tests on Bituminous Binder and their significance 104
6.5 Bituminous Mixes: 110
6.5.1 Definition and Classification 110
6.5.2 Marshal Method of Bituminous Mix Design: 111


CH-1, INTRODUCTION TO TRANSPORTATION PLANNING & ENGINEERING
1.1 Transportation Engineering
Overview:
Transportation is non separable part of any society. It exhibits close relation to the style of life, the range and location of activities and goods and services which will be available for consumption. Advances in transportation has made possible changes in the way of living and the way in which societies are organized and therefore have a great influence in the development of civilization. Transportation is responsible for the development of civilizations from very old times by meeting travel requirement of people and transport requirement of goods.
Transportability refers to the ease of movement of freight, passengers and information.
(We only consider the movement of people and goods as transportation engineering)
Transportation System may be defined as consisting of the fixed facilities, the flow entities and control system that permit people and goods to overcome the friction geographical space (to move from one place to another place) efficiently in order to participate in a timely manner in some desired activity.
Highway Engineering thus may be defined as one of the branch of civil engineering which deals with art, science and technique of planning, design, construction and maintenance of roads and highways.

1.2 Modes of Transportation
Primary Modes
Aviation (Airways),
Land Transport
Railways
Roadways
Waterways
Secondary Modes
Ropeway
Pipe line
Canal
Belt conveyer
Spaceflight

1.3 Comparison between various modes of Transportation and their Relevance in Nepal

Aviation (Airways)
In 1949 AD (2006 BS); The date heralded the formal beginning of aviation in Nepal with landing of 4-seated aircraft of Indian Ambassador at Gauchar, Kathmandu
In 1955 AD; King Mahendra inaugurated Gauchar Airport and renamed as Tribhuvan Airport
Royal Nepal Airlines Corporation (RNAC) was established In 1958 AD
Tribhuvan Airport renamed as Tribhuvan International Airport in 1964 AD.
The permission for private airlines has given on 1992 A.D.
Currently, Nepal has total of 54 Airports including 1-International airport, 5-Regional Hub airports, 43-Domestic airports and 5-under construction (Ref: Civil Aviation Report-2010). But all are not in operation, few are occasional.
Advantages:
Improves accessibility to otherwise inaccessible areas.
Provides continuous connectivity over land and water (no change of equipment)
Saves productive time spent on journey.
Relief and rescue operation.
Maximum speed: Modern jet can travel at 1000 km/h.
Safest mode of Transportation.

Disadvantages:
Heavy funds are required, not only initially but also during operation.
Operations are highly dependent upon weather conditions.
High energy consumptions.
High safety provisions are required.
Noise pollutions.
Highly sophisticated instruments and machinery are needed.

Railways
First railway was started on 1927 AD (1984 BS) at the period of Chandrashamsher from Raxaul (india) to Amlekhganj, 48 km long (46 km in Nepal).
At present a portion (29 km) of Janakpur (Nepal) to Jayanagar (India) railway (32 km in total) is in operation. This railway was constructed on 1936 AD (1993 BS). Rakxaul to Birgunj 6 km and Bijalpura to Janakpur 21 km not in operation.
Government of Nepal has completed the feasibility study on East-West and Kathmandu-Pokhara electric railway having total length of 1317.475 km
Mechi-Mahakali 945.244 km ≈945 km
Tamasariya-Bharatpur-Abukhaireni 71.729 km ≈ 72 km
Pokhara – Kathmandu 187.083 km ≈ 187 km
Connections to Indian Border Towns 113.419 km ≈ 113.5 km
Trains move on the steel tracks laid on the ground resulting in heavy expenditure on basic infrastructure.
Advantages
Trains move at much higher speed than pneumatic type vehicle on modern highways.
Steel tracks can take three to four times heavier axle loads than roads.
The energy required to haul a unit load through a unit distance by railways is about 16% on comparison to road transport.
Overall cost (initial cost, operating cost and maintenance cost) is less than that for roadways.
No steering required for controlling the movement.
Safe in comparison to road transport.
Disadvantages
Huge investment of capital.
It cannot provide a door to door service.
They need huge man power for the proper functioning.
Routes and timings cannot be adjusted to individual requirements.
Railway transport is unsuitable and uneconomical for short distances and small traffic of goods.
Because of huge capital requirements and traffic, railways cannot be operated economically in rural areas.
The ruling gradient for railways in plains is 1 in 150 to 1 in 200 and in hilly regions is 1 in 100 to 1 in 150. The steeper gradient needs more powerful locomotives, smaller train loads, lower speeds resulting in costly hauling.

Roadways
"Bagmati valley Road Project" was set up to carry out the detail survey and construction of Kanti Rajpath (Tikabhairab of Lalitpur district to Hetauda). In 1954 AD, Royal Nepal Army completed its detail survey. In 1959 BS, Rajdal Army Battalion completed the construction rough road of 70 Km of 91 Km.
First highway is the Tribhuwan Highway, which is constructed in 1950-1956 A.D.

Advantages

In comparison to other modes of transportation, road transport is the nearest to the people.
This mode has maximum flexibility for travel with reference to route direction, time and speed of travel and also provides door to door service.
The road network serves as feeder system for other modes of transportation.
Roads are used by various type of road vehicle like passenger cars, buses, trucks, animal and hand driven carts, pedal cycles, pedestrians etc.
Road transport requires relatively small investment for the construction. Motor vehicles are much cheaper than rail locomotives, coaches and wagons, water and air carriers.
For short distance travel, road transport saves time.

Disadvantages

High energy and area use.
Main source of noise and air pollution in cities.
The road transport is subjected to a high degree of accidents due to the flexibility of movements offered to the road users.


Waterways
Water transport is the process of transport that a watercraft, such as boats and ship, makes over a body of water, such as a sea, ocean, lake, canal or river. If a boat or other vessel can successfully pass through a waterway it is known as a navigable waterway.
At present few waterways are in operation for the transportation; they are:
Saptakoshi River; Chhatra-Simle: 12 km (Jet Boat)
Kaligandaki River; Mirmi-Seti Beni: 5km (Local Motor Boat)
Kulekhani Boat; Indrasarobar: 7 km (Motor Boat)
Country Boat for crossing of river
Boating in lakes in Nepal
Raft and Kayak in big rivers of Nepal
Governament of Nepal has completed the feasibility study on waterway in Nepal and found the feasible for following routes:
Koshi Basin; Saptakoshi & Sunkoshi River: 173 km
Gandaki Basin; Kaligandako & Trishuli River: 185 km
Karnali Basin; Bheri and Karnali: 123 km

Advantages & Disadvantages:
Although it is slow, modern sea transport is a highly effective method of transporting large quantities of non-perishable goods. Transport by water is significantly less costly than air transport for transcontinental shipping.

Ropeways:
Cable transport is a broad mode where vehicles are pulled by cables instead of an internal power source. It is most commonly used at steep gradient. Typical solutions include aerial tramway, elevators, escalator and ski lifts; some of these are also categorized as conveyor transport. Ropeway is the oldest transportation system.
Kathmandu Hetauda ropeway is the first ropeway in the country and was constructed during the period of 2021 B.S. (Length=42 km) Not in operation
The second public ropeway is the Manakamana Cable Car; 2.8 km long; and is continue in operation from the beginning.
Tuins is the example of ropeway in Nepal.
Pipeline transport sends goods through a pipe, most commonly liquid and gases are sent, but pneumatic tubes can also send solid capsules using compressed air. For liquids/gases, any chemically stable liquid or gas can be sent through a pipeline.
India and Nepal have decided to go ahead with the proposal for a 41-km petroleum pipeline between the two countries at a cost of around 100 crore. The pipeline is to be laid between Raxaul in Bihar to amlekhgunj in Nepal. This proposal was initially proposed by IOC in1995, pre-feasibility and technical study was carried out in 2004 and 2006 AD.
Canal transport is used to transport freight (liquid like water for irrigation) only
Belt conveyers are widely used to transport freight (Solid and liquid also) especially during construction works and works similar manner as cable transport.
Spaceflight is transport out of Earth's atmosphere into outer space by means of a spacecraft. While large amounts of research have gone into technology, it is rarely used except to put satellites into orbit, and conduct scientific experiments.
1.4 Historical Development & Construction of Highway in Nepal
The history of the road development & construction can be studied in following two aspects:
Management Aspects
Construction Aspects
Management Aspects:
During Rana period, a government body was formed in order to deal with road construction and maintenance, called Bato Kaj Goshwara and Chhembhadel Adda.
Two branches Naya Bato Kaj Goshwara and Purano Bato Kaj Goshwara was made in order to construct the new and maintain the old road networks.
In 2007 B.S., after democracy, these government agencies are combined all-together and Public Work Department (PWD) was formed.
In 2017 B.S. three subsections, named as Planning, Construction and Maintenance  were created under road section of PWD
In 2027BS, separate branch for road is felt as necessary and the Department of Road (DoR) was formed. At the same time the department of building is also formed.
At the same time the First Road Standard (Nepal Road Standard-2027) was made.
The Mechanical Training Centre (MTC) was established within the Department of Roads (DoR) under MOPPW in the year 1978 AD to equip the mechanical staff of DoR with knowledge and needed to operate.
In 2051 BS, 25 divisions of road are formed under five regional offices.
In 2067 B.S., the department of Railway is formed.
A new Nepal Road Standard is in process.
Department of Roads is planning to go for a major transformation towards a wide and broad, computed based Management Information System (MIS).
Highway Management Information System (HMIS) is in process of updating data based GIS Mapping of Nepal Road Statistics (AADT, IRI, SDI, and Type of Pavement) in terms of details of data.
Construction Aspects:
Many trails with hard surface in Nepal (particularly in Kathmandu) may have been developed during Malla’s Period, when a large number of temples were constructed. These roads consisted of hard broken brick over which flag stone slab were laid over a base of line concrete. Such roads were basically intended for horse driven carts and are still visible and in use even today.
The first motorable road was constructed in Kathmandu Valley in 1924 AD.
The 42 km long gravel road linking Amlekhganj with Bhimphedi was built in 1929 AD. Before Tribhuvan Highway was built, old travelers used the historic trade route passing through Bhimphedi, Kulekhani, Chitlang, Chandragiri Pass and Thankot.
Nepal's first highway was constructed with aid from India in the early 1956 AD. It connected Kathmandu with Raxaul on the Indian border.
Bagmati Valley Road Project was setup to carry out details survey and construction of Kanti Rajpath. In 1954 AD, Nepal Army completed its detail survey. In 1960 AD, Rajdal Army Battalion completed the construction of 70 km of 91 km (86+5 km link with valley and Tikabharab) long Kanti Rajpath from Tikabhairb (Lalitpur) to Hetauda through Bhattedada and  Jyamire.
The 113-kilometer Arniko Highway, which connected Kathmandu with Kodari on the Chinese border, was constructed in 1964 AD, with Chinese assistance.
The Siddhartha Highway was constructed in 1964 AD, with India's help and connected the Pokhara Valley with Sonauli in India's Uttar Pradesh state.
The longest highway is the Mahendra Highway, or East-West Highway. Its total proposed length was approximately 1,024 kilometers, of which 850 kilometers were completed as of 1989 AD.
As of 1997 AD, additional roads were being built, primarily with the cooperation of India but also the United States, including an East-West Highway through southern portions of the country. Other roads, in various stages of planning, construction, or already completed, were built with assistance from Saudi Arabia, India, Britain, the Soviet Union, Switzerland, China, the United States, the World Bank, and the Asian Development Bank.

1.5 Highway Planning
In the present time planning is a pre-requisition before taking up any development programme. This is more true particularly in an Engineering project and thus also for Highway development programme.
Objectives of Road/Highway Planning:
Integrated Network: It should be able to establish an integrated highway (road) network capable of accommodating all highway travel in an orderly, safe, efficient and economical way.
Future demand: It should be able to forecast the future requirement of road needed in the different parts of the country
Setting up the Priorities: It should be able to setup priorities for the construction of roads and bridges and renewal program in accordance with the available resources and the utility of the project.
Phasing of road development program: It should be able to setup schedule for phase construction of roads and bridges and renewal program in accordance with the restriction due to resource and priority.
Financial planning and management: It should be able to work out financing system

Planning of road is basically accepted as an outcome of the needs of society. There are usually a lot of needs which cannot be net at a time. The first step in planning, therefore, is to identify all present and future needs which may be reasonably foreseen and that these needs would not be overlooked or messed. Secondly, planning of road sets up the priority for undertaking the construction of roads.
Planning of road network is dealt separately for two of the following cases:
National road network planning
City (Urban) or local network planning
National Road Network Panning
National road network has to be developed based on the careful study and thorough knowledge of traffic engineering such as:
Trip generation
Origin and destination study
Traffic composition
Traffic measurement
Traffic desire line or density
Traffic planning
The first case of planning encompasses all roads to be developed in the national context which includes National Highways, Feeder Roads, Urban Roads, District Roads and Village Roads. The National Highways together with the Feeder Roads constitute the Strategic Road Network (SRN) of the country. The Strategic Road Network is the backbone of the National Road Network. The construction and maintenance of the strategic roads fall on the responsibility of the Department of Roads, Ministry of Physical Planning and Works (MoPPW) while the construction and maintenance of District and Village roads fall under the agencies under Ministry of Local Development (MoLP).
Although strategic roads constitute 33% of the National Road Network, It plays a very important role in terms of the movement of people and freights. The strategic roads have high volume in comparison to district roads. At present, the strategic road network consists of 15 National Highways and 51 Feeder roads totaling 4806 km (constructed) of about 5225 km.
National Highway
There are 15 National Highways (NHs) in Nepal with total length 2671 km of about 3451km, of which more than 70% is bituminous. The name, origin, destination and length of National Highways are illustrated in table below:
S.N. Name of the Highways Length (km) Start Point Finish Point Remarks
1 Mahendra Rajmarg 1028 Mechi Border, Jhapa Gaddachauki Border, Kanchanpur
2 Tribhuvan Rajpath 160 Birgunj Border,Birgunj Kathmandu 29 km overlap is skipped
3 Prithvi Rajmarg 174 Pokhara Naubise
4 Araniko Rajmarg 113 Kodari Border Kathmandu
5 Siddartha Rajmarg 182 Sunauli Border Pokhara
6 Mechi Rajmarg 268 Kechana Border Taplejung
7 Koshi Rajmarg 112 Rani Border, Biratnagar Hile
8 Sagarmatha Rajmarg 265 Kadmaha, Saptari Solu-Salleri, Solukbhumbu 54 km completed
9 Dhulikhel-Sindhuli-Bhittamod Rajmarg 198 Bhittamod Border, Jaleshor Dhulikhel 136 km completed
10 Narayanghat-Mungling Rajmarg 36 Pulchowk, Narayanghat Mungling
11 Rapti Rajmarg 196 Ameliya, Dang Musikot, Rukum 169 km completed
12 Ratna Rajmarg 113 Jamuniya Border, Nepalgunj Bangesimal, Surkhet
13 Karnali Rajmarg 220 Bangesimal Surkhet Jumla 113 km completed
14 Seti Rajmarg 66 Dadeldhura Samuwagadh
15 Mahakali Rajmarg 320 Dhangadhi Border Darchula 308 km completed
Feeder Roads:
Feeder roads (FRs) include Feeder roads major and Feeder roads minor. There are altogether 51 Feeder roads with about 2000 km in length.
S.N. Name of the Feeder Road (with Origin and Destination) Length (km) Development
Region
1 Birtamod-Chandragadhi 13 Eastern
2 Damak- Gauriganj 22 Eastern
3 Bhardaha- Rajbiraj 18 Eastern
4 Rupani- Malhaniya 23 Eastern
5 Chaurahawa- Mardar 27 Eastern
6 Nawalpur-Malangawa 27 Central
7 Chandranigahapur- Gaur 44 Central
8 Birdaghat- Harpur 23 Central
9 Sunwal- Parasi 9 Western
10 Jitpur- Khunuwa 33 Western
11 Gorusinge- Sandhikharka 69 Western
12 Chanua- Krishnanagar 20 Western
13 Bhaluwang- Rolpa via Chakchake 108 Mid-Western
14 Chakchake- Pyuthan 23 Mid-Western
15 Lamahi- Tulsipur via Ghorahi 47 Mid-Western
16 Bhurigaun- Gulariya 32 Mid-Western
17 Junga- Rajapur 28 Mid-Western
18 Birgunj- Kalaiya 12 Central
19 Bhainse- Bhimphedi 12 Central
20 Palung- Kulekhani 21 Central
21 Tripureshor- Dhunche 117 Central
22 Balkhu- Dachhinkali 16 Central
23 Satdobato- Tikabhairab 12 Central
24 Satdobato- Phulchoki via Godawari 22 Central
25 Maharajganj- Budhanilkantha 5 Central
26 Chabahil- Sankhu 13 Central
27 Jorpati- Sundarijal 7 Central
28 Bhaktapur- Nagarkot 23 Central
29 Banepa- Khopasi 10 Central
30 Panchalkhal- Helambu 31 Central
31 Dolalghat- Chautara 25 Central
32 Lamosangu- Ramechhap 130 Central
33 Tamakoshi- Jiri 38 Central
34 Malekhu- Dhadingbeshi 20 Central
35 Abukhaireni- Gorkha 25 Central
36 Dumbre- Behisahar 43 Western
37 Bharatpur- Bypass 4.5 Central
38 Fikkal- Pashupatinagar 11 Eastern
39 Biratnagar- Rangeli 24 Eastern
40 Hile- Tehrathum 48 Eastern
41 Pokhara- Sarangkot 5 Western
42 Pokhara- Beni via Banglung 90 Western
43 Bartung- Tamghas 80 Western
44 Bhairahawa- Paidariya 23 Western
45 Lumbini- Taulihawa 25 Western
46 Nepalgunj- Gulariya 35 Mid-Western
47 Chinchu- Jajarkot 107 Mid-Western
48 Surkhet- Dailekh 64 Mid-Western
49 Khodpe- Chainpur 110 Far-Western
50 Santbang- Jumlaghat 42 Far-Western
51 Silgadhi- Sanfebagar 87 Far-Western
Urban Road Network Planning
Essentially, all urban areas are communication centers for the exchange of goods, services and ideas. Higher the level of these activities greater will be the city or town. Planning of urban road network should consider the extent of town, future expansion possibilities.
Based upon the function that the urban road serve; it is of following types
Arterial Road
Sub-arterial Road
Collector Street
Local Street
Arterial and sub-arterial streets primarily for through traffic on a continuous route, but the sub-arterials have a lower level of traffic mobility than the arterials. Collector streets provide access to arterial streets and they collect and distribute traffic form and to local streets which provide access to abutting property.
Many old towns/cities were developed slowly without any road plan. Road network plan in such cases may not take any definite grid or circular shape.
New towns and cities are developed with definite road patterns.
The expansion of existing and old town/cities resembles to some of the patterns in the recent development process keeping or improving to some extent the central core network as needed. As we have seen the road network of Kathmandu is being developed in a definite pattern in the recent past though in the central core area the same cannot be grouped in any of the standard patterns.
Broadly, two principle types of major road pattern are developed in modern urban areas;
Grid Iron pattern
Rectangular
Hexagonal
Radial pattern
Star and block
Star and circular
Star and grid
Linear pattern
Grid Iron Pattern:
The simplicity in layout of this type of network has been acknowledged by all physical planners and architects. The buildup area is obtained in a rectangular shape which is easy to develop
Although the grid iron pattern can produce monotonously long streets flanked by dull (boring) blocks of buildings, it has considerable traffic moving advantages. It encourages an even spread of traffic over the grid, and as a consequence, the impact at a particular location is reduced. If there is central business area in the middle of the grid, it is relatively easy for through traffic to bypass it since there are usually alternative bypass routes available in all four directions.
One disadvantage of the grid iron pattern is that extra distances must be travel when going in a diagonal direction. However this drawback can be eliminated by providing major diagonal routes upon the grid. But the architecture of the city may be disturbed.   (a) Rectangular Grid Pattern (b) Hexagonal Grid Pattern  Fig: Typical Road Patterns: Grid Iron

Radial Pattern:
       (b) Stat and Circular
Fig: Typical Road Pattern: Radial

The highway system in many countries was being developed in the form of network of roads connecting town to town center. Thus any given town may have several roads radiating from its center to other towns and villages about it. Eventually as the towns grew in size, they turned first to develop along radials and then to fill the spaces between.
In this system of road the main traffic generator is located within the central area and since all radiating roads converge on the main business area of focal point or diverge from it, lack of suitable bypass routes for through traffic produced the belief that the cause of central area congestion was traffic on radial routes not necessarily having desires to reach the central but to some other villages or town in lateral direction. The solution for this problem is to build ring roads around the central business area as needed.

Ring Roads
By definition a ring road is a link that is roughly circumferential bout the centre of the urban and which permits traffic to avoid the centre of this area.

Depending upon the extent of population a single ring road, double, triple, quadruple ring roads in series may be provided. For example town of about 50 to 100 thousands a sing ring road may be sufficient whether a city of 2.5 millions preferably require two ring roads. The population of Kathmandu valley is 2.51 million (Population Census-2011) was 1.6 million in 2001.
The length of existing ring road of Kathmandu Valley is 27 km and the proposal for outer ring road is about 72 km.
The principle advantage of radial system having provision of direct access to the town centre, initially envisaged (imagined) is becoming problem responsible for traffic congestion. Most offices, institutions, shopping complexes are centered around the central core business area.During peak periods, especially, as the radial road is followed inward, the traffic volume builds up progressively until the central area reached. The old town likes Kathmandu the meant that the greatest accumulation of vehicles occurs where road conditions are most critical and where the provision of additional road space is almost beyond the country’s economy or become the subject of public antipathy (opposition).
         
The principle advantage of a ring road lies in its ability to serve a central area while circumventing it. This is explained by diagram as below: which shows some possible routes of travel from an origin point ‘O’ outside a central area enclosed by a complete circular ring road of radius ‘r’ on destination point ‘D’ inside the ring road. If it  is assumed that the destinations are scattered random over the central area, then the theoretical average distances traveled from point ‘O’ to a destination ‘D’ located within the circle as shown in figure. From the figure it is seen that the ring road route is appreciably longer than other routes. However it has a particular advantage that only 0.33*r is on the edge of the area, and thus, in theory, should be free of the central area congestion problem.
Linear Pattern:
It is characterized for old towns or unplanned cities. The linear pattern is obsolete.


1.6 Classification of Highway in Nepal
NRS Classification of Roads:

Feeder Roads serve the community’s wide interest and connect District Head- quarters and/or Zonal Head-quarters and/or other important centers (Powerhouse, Tourist Center etc.) to National Highways.
District Roads consisting of all roads not defined as National Highways or Feeder and city roads, serves primarily by providing access to abutting land carrying little or no through movement.
Urban roads within the urban limit of municipality boundary, except for the above classes, passing through the city. These roads provide access to abutting residential, business and industrial places within municipalities.
Village road includes non-through roads linking single villages directly to the district roads.
According to Nepal Roads Standard-2027, First Revision-2045; the roads in Nepal has classified into 4-categories: National Highway, Feeder Roads, District or Village Roads and City Roads.

The five classes of Rural Transport Linkages (as per Nepal Rural Road Standard 2055):
















CH-2, HIGHWAY ALIGNMENT AND ENGINEERING SURVEY
2.1 Highway alignment and controlling factors
2.2.1 Introduction:
The fixing of the position of the center line of the highway on the ground is called highway alignment. During highway alignment following factors are considered:
Road should be straight to minimize the length.
A road can be curve to consider the neighboring village, local market etc.
Aligned road should cross the road canal, rivers etc at right angle.
Aligned road should be away from fertile land.
Aligned road should not cross the swampy area.
Aligned road should be in balance position with respect to cutting and filling.

2.1.2 Requirements of Highway Alignment:
The requirement of highway alignment is short, easy, safe and economy (SESE)
Short: The alignment should be minimum between two terminal points.
Easy:  The alignment should be such that it should be easy to construct and maintain the road with minimum obstruction.
Safe:  The alignment should be safe for construction and maintenance from the view point of stability of natural slopes.
Economical: The aligned road should be considered economical only if the total cost (initial cost, maintenance cost and vehicle operation cost is lowest.

2.1.3 Factors controlling road alignment
For an alignment to be shortest, it should be straight between the two points. Due to certain practical and economical problems, it is not possible to follow the straight path. The various factors that control the highway alignment are as follows:

Obligatory Points: These are certain points governing the alignment of highways. These control points are classified into two categories :
Points through which the alignment is to pass (Positive obligatory point): It is the point from where road has to pass like bridge, commercial place etc. The road bridge across a river can only be placed where the river has straight and permanent path and where the bridge abutments and pier can be properly founded.

Points through which alignment shall not pass (Negative obligatory point): It is the point from which road can’t pass i.e. road deviate from these points. The obligatory points which should be avoided while aligning a road include religious places, very costly structures, unsuitable lands and water logged area.

Traffic: The alignment should suitable for traffic requirements. During alignment of new road desire lines, traffic flow patterns and future trend should be considered seriously.

Geometric Design: Geometric design factors such as gradient, radius of curve and sight distance also governs the alignment of road. If the straight alignment is aimed at, often it may be necessary to provide very steep gradients. The gradient of new road should be flat and less than ruling or design gradient. The absolute minimum sight distance, which should invariably be available in every section of the road, is also accepted.  Thus it may be necessary to change the alignment in view of the design speed and super elevation. It may be necessary to make adjustment in the horizontal alignment of road keeping in view the minimum radius of curve and the transition curves.

Economy: The alignment finalized based on the above factors should also be economical. In working out the economy, initial cost, the cost of maintenance and vehicle operation cost should be taken into account.

Other factors: Other factors hydrological, drainage consideration, subsurface water level, seepage flow, high flow level, foreign territories etc are the factors to be kept in view.

In case of hill road the factors like stability, drainage, length, geometric standard etc are also considered beyond the above mentioned factors.

2.2 Highway survey
2.2.1 Structure of Route Location Process:
In general, the approach to selecting the route for a highway can be described as a hierarchically structured decision making process. This is very logical approach is easiest described by referring to figure 2.4.
As in figure below, the first step in the process of route location is the fixing of the starting point and end point. The region is then fixed, which includes all the possible routes including starting and ending point. The required number of bands about 8 to 16 km wide is selected based on the terrain or the nature of the ground.

In order to concise the route, required number of corridors are selected about 3 to 10 km wide within each band. Some of the corridors that are not much important are omitted and best of the corridors are chosen. Route strips of about 1 to 1.5 km wide is then fixed within selected corridors, generally one or two corridors are only taken into account for route strips. In the most appropriate route strip, few aliments are fixed about 30 to 50 m wide, and this is the last step of route location process. Most appropriate alignment (s) is selected and recommended for taking out the survey work.
It is thus, seen that the process of locating a highway route involves continuous searching and selecting, using increasingly more detailed information and knowledge at each decision making stage. Factors influencing the selection of route at any instance include not only such tangibles as topography, soil, geology, land use, population distribution, travel demand, user’s cost, structure and maintenance costs, safety etc, but also intangibles such as political, social environmental factors.

2.2.2 The stages of engineering survey are:
The alignment of highway is finalized based on different survey. Survey should be done in a right way to achieve the requirements as much as possible. There are four stages of survey which decide the alignment. The first three stage of survey consider all possible alternative alignment while the fourth stage survey is forced to detailing. Therefore, fourth stage is called final location and detailed survey
Map Study: With the help of topographic map, the possible route of road can be decided which helps in further study. The possible alignment can be located on the map as following details are available from map:
Alignment should avoid valley, ponds or lakes etc
Approximate location of bridge site for crossing river
When a road is connected between two stations, one on the top and other on the foot of hill, then alternate route can be suggested keeping in view the permissible gradient say ruling gradient.
Map study thus gives a rough idea about various routes which require further survey work.

Reconnaissance: The second stage of survey is reconnaissance. It is the process of evaluating the feasibility of one or more possible routes for a highway between specific points. In reconnaissance survey fairly wide stretch of land along all the marked routes is studied. In reconnaissance survey instrument like hand level, tangent clinometers, abney level etc are used. All relevant information not available in the maps are collected during reconnaissance which are as follows:
Villages, ponds, lakes, ridge, fall and other obstruction along the routes.
Approximate value of gradient, length of gradients and radius of curve of alternate gradients.
Maximum flood level and number and types of cross drainage works along the routes.
Types of soil and geological features.
Position of quarries which are the source of stones, water and source of construction materials are also marked.
For hilly areas, additional data like geological formation, types of rock, seepage flow, slope of the hill, rainfalls etc are also collected.
From data collected in the reconnaissance survey, proposed alignment marked during map study may be altered at few points of may be completely changed and finally one or more alternative routes may be proposed for the further study.
Preliminary Survey: It is a large scale study of one or more feasible routes. It consists of running accurate traverse line (base line survey) along the route already recommended by the reconnaissance survey in order to obtain sufficient data for final location. The main purpose of preliminary survey are:
To survey the various alternate alignments proposed after the reconnaissance and details about gradient, sight distance, curve radius, cross drainage works and types of soils are collected.
To compare the different proposal in view of the requirement of a good alignment.
To eliminate quantity of earth work materials and other construction aspects.
To finalize the best alignment from all consideration.
There are two methods of preliminary survey:
Conventional/Ground Survey Method
Aerial Survey (Aerial photograph)
Steps in Preliminary Survey by conventional method
Preparation of baseline traverse for each of the recommended alignment as a result of reconnaissance survey. Since the traverse in road alignment is of open type no adjustment can be made later it should be done accurately.
Leveling along the baseline traverse to obtain the center line profiles and typical cross-sections to obtain the approximate earthwork in the alternate alignments.
Collecting topographical and other details.
Drainage study and collection of hydrological data.
Soil survey/Geological study is done but detailed soil survey at this stage is not essential. Soil survey helps in structural design of the pavements.
Material survey
Traffic survey
Steps in Preliminary Survey by aerial method
Taking aerial photographs of the steps of the map.
The photographs are examined under stereoscope and control points are selected for establishing the traverse of alternate proposal.
Geological characteristics, soil conditions, drainage requirement etc can be decided on the basis of photo interpretations.

Final Location and Detailed survey
These surveys solves a dual purpose by fixing the center line of the road while at the same time physical data are collected which are necessary for the preparation of complete construction plan, profiles, cross-sections and road structures. The alignment finalized as a result of preliminary survey is first of all located on the field and then its detailed survey is carried out.  During detailed survey following works are performed.
Pegging the center line
Centerline leveling
Cross-sections
Property lines
Temporary water courses and stream details
Material site survey
Special site survey (Heavy structure)
CBR value of soils along the alignment may be determined for designing the pavement.

2.4 Class-Work on Alignment Selection
The selected routes from a contour map always follow contour lines, as the quantity of cutting and filling has to be minimized. As discussed in heading Highway alignment survey, the first stage is to carry out the study of map. The study of map is directly concerned with the route location process, and thus selection of regions, bands, corridors and route strips. Final detailed survey is carried out only for the selected route from route location process.

2.2 Identification of Road Project and Feasibility Study:

Identification of Road Project: A highway or urban road project is identified on the basis of national network plan and city network plan which are usually developed by transportation planners and approved by the National Planning Commission.
In order to form the basis for planning, identification of the project and feasibility from technical aspect, need for construction, set up priorities etc series of surveys and studies are carried out. For a large scale project, conducting detailed feasibility study in the first attempt will not be desirable as it involves high cost. A pre-feasibility study is carried out to get the tentative idea on the feasibility of undertaking project. If the result hints towards positive aspect then the feasibility study is carried out in the second stage.
In order to prepare the feasibility study report one should be familiar with various methods of Cost-Benefit Analysis:
Net Present  Value (NPV)
Internal Rate of Return (IRR)
Benefit Cost Ratio (BCR)
Payback Period


2.5 Components of an Economic Appraisal:
The following components of economic appraisal can be quantified and converted into monetary values easily. Educational, Societal Environment and general community values are not included in economic analysis since they cannot be reduced to supportable and realistic monetary values.
Cost of highway construction
It includes both initial cost items and subsequent maintenance cost.
Initial cost item includes:
Land
Main works contract
Ancillary (auxiliary/subsidiary) works contract
Work by other authorities
Administration and preparation
On-site supervision and testing
Maintenance cost includes:
Non traffic related cost
Traffic related cost
Evaluation of road user benefits
The benefits can be obtained from the existing volume of traffic as well as from the increased volume due to diverted and generated traffic. In case if the economic analysis is done for two cases having no road link and a new link, additional components like-increase in agriculture production benefits from new development etc also has to be considered.
Road user operating cost
Vehicular operating cost:
Fuel cost
Oil cost
Tires
Maintenance
Depression
Value of money
Hiring cost of driver
Hourly rental of equipment
Accident costs
Loss of output due to death or injury
Cost of hospital service, ambulance, police, administration and property damage
Cost of pain, grief and suffering to the casualty, relatives and friends (not tangible)
Traffic data
Traffic flows:
Volume
Composition
Directional distribution
Speed and delay
Number of accidents

 
3.0 GEOMETRIC DESIGN
3.1 DEFINITION AND SCOPE:

Geometric design is that stage of highway design which deals with the visible dimensions of roads. It is the design of those road elements which a road user is directly concerned and does not include the design of pavement, structural and drainage components and so on. In the process of geometric design, various geometric elements or dimensions of road are determined in consideration with traffic requirements, road users' behavior, safety, speed, economy and comfort.

Various features of the road elements can be categorized onto three broad groups:
Elements of Cross-Section
Pavement surface characteristics
Traffic lane, Carriageway, Shoulder, Median-strips, Right of Way, Side Slope
Camber
Super elevation
Extra widening of horizontal curves
Laybys
Noise Barriers
Sight Distance across the road
Elements of Horizontal Alignment
Straight Line/ Tangent
Turning Angle/ Deflection Angle
Radius of Horizontal Curve and its Length
Transition/Easement Curve and its Length
Sight Distance along the horizontal alignment
Elements of Vertical Alignment
Grade
Vertical Curves (Summit Curve and Valley Curves)
Sight Distance along the road profile

3.2 CONTROLS AND CRITERIA FOR ROAD DESIGN
3.2.1 Factors which controls the geometric design:
Design Speed
Road Type and Topography
Design Vehicle
Traffic Volume and Composition Traffic Factors  
Road user behavior
Traffic Capacity
Safety Considerations
Environmental Considerations
Economic Considerations
*Sometimes Design vehicle, traffic characteristics and road user behavior are combinely taken as traffic factors

Designed Speed:
Designed Speed is the maximum permissible safe speed for a light vehicle for a given road. As per NRS-2045, Design Speed in kmph for different types of road in different terrain has given below:

Types of Road Design Speed (kmph) for different Type of Terrain
Plain Rolling Mountainous Steep
National Highway 120 80 50 40
Feeder Roads 100 60 40 30
District Roads 60 40 30 25

The design speed depends upon the following factors:
Type of the road and terrain
Width and clearance requirements of road
Sight distance required
Type of curve along road
Nature, type and intensity of traffic
Road Type and Topography:
NRS defined road into 5 different categories; NH, FR, DR, CR. The Right of way for NH is 50 m, that for FR it is only 30 m, and that for DR is only 20 m. Similarly the designed speed, maximum permissible gradient also depend on the type of road. This is given on Nepal Road Standard 2027.
Topography∷∷∷∷∷∷∷∷∷∷






Design Vehicle:
Designed vehicle are those vehicles which affect the design elements of road.
Length of vehicle affects ¬--> Extra widening of Curves
Width of vehicle affects --> Width of lane (3.75 m)
Height of vehicle affects --> Vertical clearance (4.75 m)
Weight of vehicle does not affect in geometric design but affects on pavement design

Traffic Volume and Composition:
Traffic volume is the number of vehicle crossing a section of road per unit time at any selected period. It is the measure of traffic flow. The units of measurement are:
Average Daily Traffic (ADT)
Annual Average Daily Traffic (AADT)
Peak Hour Traffic (PHT)
15 minutes traffic volume
30th hourly traffic volume

Road User's Behaviors:
The extent of influence of road users' behavior in determining the geometric elements of the road cannot be quantified but the effect cannot be ignored.

Traffic Capacity:
= (Capacity of traffic lanes); It is the sum of the capacities of each lane
Theoretical Capacity; "C="  "1000V" /"S"
Where; V = Speed of vehicle in kmph
S = Centre-to-centre spacing of vehicles in m
  = Length of vehicle + Sight Distance

Safety Considerations
It is the considered as the very much important parameter for designing the road geometry. It includes the following parameters:
Highway safety act (not practice in Nepal)
Policy information
Highway should be designed to minimize driver decisions and to reduce unexpected situations
Traffic signs and signals

Environmental Considerations
Air pollution, noise pollution, landscaping and other local considerations:
Physical Features: valleys, ponds, river crossing, slope
Manmade Features: historical monuments, buildings, other structures

Economic Considerations
The benefit for the user and the investor is another important factor to be considered during the design of the road. But some strategic roads are constructed without taking the benefit analysis.
3.2.2 Criteria for geometric design:
Speed
Safety
Comfort
Economy
3.3 & 3.4 TYPICAL CROSS-SECTIONAL ELEMENTS:
Pavement Surface Characteristics:
friction or skid resistance
Skid occurs when the slide without revolving or when the wheels partially revolve i.e. when the path travelled along the road surface is more than circumferential movement of the wheels due to their rotation.
Slip occurs when a wheel revolves more than the corresponding longitudinal movement along the road.
For calculation of sight distance longitudinal coefficient of friction is taken to be 0.35-0.4
In the case of horizontal curve design the IRC and NRS recommend the value of coefficient of lateral coefficient to be 0.15

pavement unevenness
The pavement surface condition is commonly measured by using equipment called Bump Integrator, in terms of unevenness index, which is cumulative measure of vertical undulations of the pavement surface recorded per unit horizontal length of road.
150cm/km is for good pavement surfaces of high speed highway whereas 250 cm/km is satisfactory up to speed of 100 kmph.

light reflecting characteristics
Night visibility very much depends upon the light reflecting characteristics of the pavement surface.
Light colored or white pavement give good visibility at night but during bright sunlight it produce glare and eye strain
Black top pavement has no glare effect but has poor visibility at night especially when it is wet.

Traffic lane (TL):
It is the strip of the carriageway occupied by vehicles moving in a single stream along the road.
TL= f(width of vehicle, safety clearance on either side)

Width of Carriage Way(C/W) or Width of Pavement:
It may be defined as that strip of road which is constructed for the movement of vehicular traffic. The carriageway generally consists of hard surface to facilitate smooth movement and is made of
either hard bituminous treated materials or cement concrete. It is also called Pavement width.
By definition;
Carriage way=n*TL where; n= no of lanes
TL=width of single lane


Shoulder:
It is the portion of roadway on either side which is periodically used by vehicles during crossing, overtaking and parking maneuvers. Shoulder is an important element of rural road. Laybys are the intermittent shoulders provided in hill roads. Laybys are provided as continuous shoulder cannot be provided in hill roads.
In practice in Nepal; width of shoulder = 0.5 to 1.5 m

Advantages of Shoulder:
Provides space for parking vehicles during repair etc
Capacity of road increased because of frequently available opportunity for overtaking
Sufficient space available for parking vehicles on rest
Provides space for fixing traffic signs away from the pavement
Shady trees can be grown up away from the pavement
Provides sufficient space for confidence in driving
Proper drainage strengthen the life of the pavement
Increased effective width of carriageway
Lateral clearance increases the sight distance

Roadway:
It is the portion of road which is covered by carriageway and shoulders on both side and the central reservation (median, strip etc) if any. It is the top width of road measure perpendicular to the axis of road at the finished road level.

Formation Width or Width of Road Bed:
Formation width is the top width of the road embankment or bottom width of road cut measured at the finished sub-grade level over which carriageway is constructed. The width of formation for the same road may vary depending upon the side slope and thickness of the pavement structure. For low cost roads such as earth or gravel roads width of formation is equal to the roadway width.




Side Slope of fill or cut:
Hinge point    Carriageway      Shoulder               back
Front slope        slope
Toe of slope

Ditch bottom






Fig: Side slope of Fill Fig: Side slope of Cut


Laybys:     Laybys are nothing but intermittent shoulders sufficiently wide and long provided to meet the important functions of a shoulder where the continuous shoulder on either side cannot be provided from economical point of view. Laybys are elements of hill roads in Nepal.
Right of Way (RoW) or Land Width (differ from lane width):
The strip of land on either side of road from its centre line (CL) acquired during road development and which is under the control of road authority (DoR Nepal)
National Highway =25 m on either side
Feeder Roads = 15 m on either side
District Roads = 10 m on either side
City Roads = as NH for 4-lane and as per FR for 2-lane


Right of way may be used for the following purposes:
to accumulate drainage facilities
to provide frontage roads/driveways in roads with controlled access
to develop road side arboriculture
to open side burrow pits
to improve visibility in curves
to accommodate various road ancillaries
to widen the road where required in future with no compensation for property
Superelevation ……… Explained in 3.4.4
Camber ………………. Explained in 3.4
Extrawidening………… explained in 3.4.5

Elements of Cross-Section (only in Urban Roads)
Sidewalk or Foot Path:
It is that portion of urban road which is provided for the movement of pedestrian traffic where the intensity is high.

Kerb:
It is that element of road which separates vehicular traffic from pedestrians by providing physical barrier (15-20 cm)

Median Strip (or Traffic Separator or Central Reservations):
It is the raised portion of the central road strip within the roadway constructed to separate traffic following in one direction from the traffic in opposite direction.

Miscellaneous Elements:
Outer separator: C/W and service road separator Side strip
Parking lanes: Off-street and on-street parking Bus laybys
Service road or access road

DESIGN OF CAMBER OR CROSS SLOPE OR CROSS FALL

It is the convexity provided to the road surface and it may be defined as the slope of the line joining the crown (topmost point) of the pavement and the edges of pavement.
Types:
Straight line camber
Parabolic camber
Composite camber
Amount of camber depends on the following factors: n = f(c/w, i)
type of road
intensity of rainfall








Preparation of Camber Board:
1. Straight line Camber:
x  y  R
w/2 w/2
From fig: tan⁡θ⁡〖=R/(w/2);as θ is very smalll∶tan⁡θ→θ=n〗  (say)

                           then n=y/x=R/(w/2)=2R/w
hence y=nx=2R/w*x …………………………………….(i)

2. Parabolic Camber:
A camber with the slope of a simple parabola (i.e. a quadratic parabola) may be defined as a parabolic camber. It is provided in a low cost road and single lane or double lane roads.
y=a*x2                                                                                                        x
From fig "y" /x^2 ="R" /〖(w/2)〗^2 ="4R" /w^2                                                               y                  R
                                                                                                                                                 
             w/2 w/2                        
"y="  "4R" /w^2  "*" x^2=2/w "*"  2R/w "*" x^2=2n/w*x^2                      

3. Composite Camber:
It may be composed of partly parabolic and partly straight or two straight line cambers having different slopes. Generally asked in exam as numerical problem.

m% m%
n% m<n n%

w/4 w/4 w/4 w/4
Necessity/Advantages of Camber:
to drain of surface water quickly
to prevent infiltration into underlying pavement layers and sub-grade
to give the driver a physiological feelings of the presence of two lanes
to improve the road appearance

Disadvantages of providing heavy camber:
Central portion of road is excessively eroded
Causes uncomfortable side thrust drag
Overtaking operations may be dangerous, especially in two lane roads
There is possibility of overturning and skidding of vehicles
Low cost surface and shoulder will be excessively eroded due to increase velocity of water. This may leads to formation of cross.
Tendency of driver to travel through centre line of road. So centre line area undergoes more wear and rear.
Problem-1:
In a region of Nawalparasi district; a single lane gravel road is to be constructed. Find the camber at the centre given the RL of edge =1299.990 m. Assume suitable data if necessary.
Solution:
For gravel road; let the camber be provided at the rate of 4% (NRS)
and for single lane road; width of pavement = 3.75 m (NRS)
Then by straight line relation;
y=nx=4/100*3.75/2=0.075 m=7.5 cm
Hence; The RL of centre is = 1299.990 + 0.075 = 1300.065 m.

Problem-2:
If n=2.5% is provided in a parabolic camber of given figure, calculate the camber at the centre. Given width of pavement = 7.0 m.
Solution:
Camber at centre = "y"=2n/w*x^2=2*2.5/(100*7.0)*〖3.5〗^2=0.0875 m
Problem-3:
For a composite camber of above 3rd figure; if m = 2% (parabolic camber) and n = 3% (straight line camber) calculate the RL of points A, B, C, D. Given the RL of point E = 1111.111 m and width of camber W = 14.000 m.
      E
Solution: C       D
Height difference between A & C
= n*x = 3/100*3.50=0.105 m.      A          B
Height difference between C &D   3.5m 3.5m 3.5m 3.5m
.=2m/w' 〖x'〗^2=2*2/100*(3.5*3.5)/7.0=0.07 m w' = 7.0m

Hence:
RL of point E = 1111.111 m
RL of point C and D = 1111.111 – 0.070 = 1111.041 m
RL of point A and B = 1111.041 -0.105 = 1110.936 m




3.4 ELEMENTS OF HORIZONTAL ALIGNMENT

Provision of horizontal curves at deviation points enhances comfort to the passenger by avoiding sudden change in direction. Similarly, it helps o reduce mental strain produced by travelling monotonously along the straight route.

Curves are provided in each and every points of intersection of two straight alignments of roads in order to change the direction. Curves are needed when deviations in horizontal alignment are encountered due to various reasons as:
Topography of the terrain
Restrictions imposed by property
Making use of existing right of way
Minimizing quantity of earthwork
Need to provide access o the particular locality
Other factors controlling highway alignment
Maintaining consistency with existing topographical features of the terrain blending with existing topographical or other features)

Classification of Highway Curves:























3.4.2 Design of Horizontal Curves:
When superelevation is not considered:

Centrifugal force; (in kg) P= (mv^2)/R=(wv^2)/gR ; w=weight of vehicle in kg
p/w=v^2/gR; p/w=centrifugal ratio or impact factor
The centrifugal force acting on a vehicle negotiating a horizontal curve has two effects:
Tendency to overturn the vehicle outwards about the outer wheel
Tendency to skid the vehicle laterally outwards
Overturning effect
The overturning moment due to centrifugal force = p*h
The resisting moment due to weight of vehicle = w*b/2
The equilibrium condition to overturning will occur when ph = w*b/2
  or p/w=b/2h
This means that there is a risk of overturning when the centrifugal ratio, p/w or v^2/gR  attains a value of b/2h
Transverse skidding effect:
From Fig:
p=F1+F2=fR1+fR2=f(R1+R2)=f.W
So p/w=f and also we know p/W=v^2/gR
On combining above two conditions: we have
.v^2/gR=f or ;V^2/127R=f
Comfort to the passenger; f should be limited to 0.15 and at extreme condition 0.20
Economy in travel; f = 0.1
b


                                                                                                                                     P
                                                                               F1+F2 h

 Radius (R)  
       R1        W     R2
From fig                                            
         P = F1+F2 = f.R1+f.R2 =f*W
Hence;
P/w = f

Result:
To avoid overturning and lateral skidding of horizontal curve, the centrifugal force should always be less than b/2h and f.
When superelevation is considered:
The derivation has shown in coming page; the only result has given here
v^2/gR=f+e or ;V^2/127R=f+e
3.4.3 Sight Distance

Restriction of the sight distance at the road condition
At horizontal curve
day/night condition
good/bad weather
At vertical Curve
day/night condition
good/bad weather
Uncontrolled intersection
Types of sight distance
Stopping Sight Distance
Overtaking Sight Distance
Passing Sight Distance
??
Decision Distance
Sight Distance depends on:
Features of the road ahead
Height of the driver’s eye above road level
Height of the objet above road level




Stopping Sight Distance (SSD)

Factors affecting the sight distance
reaction time .................................... (t) ........................ 2-4 seconds
braking efficiency of vehicle ................ (η)
slope of road .................................... (i)
coefficient of friction (flongitudinal) .........(f) .......................... 0.35-0.4
speed of vehicle/vehicles ..................(V) in kmph and (v) in m/s

Stopping sight distance is the sum of lag distance and breaking distance
SD=l1+l2; l1=lag distance =v*tr
l2=breaking distance
Let F1 be the frictional force developed and f be the coefficient of longitudinal friction, l2 is the breaking distance; f=F1/w
work done against friction F=F1*l2=f*w*l2 ................................... (i)
The amount of friction force should be sufficient to resist or dissipate the energy required by the vehicle.
KE=1/2 mv^2=1/2*w/g* v^2 ........................................................... (ii)
Equating (i) and (ii)
f*w*l_2=1/2  w/g v^2⇒ l_2=  v^2/2gf
Therefore;
SD=l1+ l2 = v * tr +   v^2/2gf= 0.278 * V * tr +   V^2/254f
This expression is applicable when the road is on a leveled surface. If the road has a gradient i and the brake efficiency η in meter
SD= 0.278 * V * tr +   V^2/(254(f±i)η)
Relation between sight distance and stopping distance;

Two way traffic in a single lane
SSD = 2*SD
Two way traffic in two way lane     2*SSD
SSD = SD (stopping sight distance or non-passing sight distance
Problem-1:
Determine the SSD for a level road, for which the design speed is 40 kmph. The coefficient of friction between road surface and the tyre may be taken as 0.4. The reaction time of the driver may be assumed as 3.0 seconds. (i) The road has two lane and two way traffic
(ii) Single lane road having two way traffic
Solution:
we know;
 For level road;         SSD=Rection distance+breaking distance
= 0.278Vt+((0.278〖V)〗^2)/2gf=0.278Vt+V^2/254f
=0.278*40*30+〖40〗^2/(254*0.4)=49.11 m≈50 m (say)
For two way two lane road; SSD = 50 m
For Single lane road having two way traffic = 2*50 m = 100 m

Problem-2:
Find out the stopping sight distance for a road for which the design speed is 55 kmph. The brake efficiency may be taken as 50% and the reaction time of driver be taken as 2 seconds.
Solution:
Given; V=55 kmph
η=50%=0.5
t = 2.0 seconds
Here f is dependent upon η; Hence
SSD=0.278Vt+(0.278V)^2/2gη=0.278*55*2+(0.278*55)^2/(2g*0.50)=46.2+24.2=70.4 m

Problem-3:
Find out the stopping or non passing sight distance for a highway having a 6% descending gradient with the following data:    
Designed speed =85 kmph
Reaction time for driver =4 sec
Coefficient of friction between road surface and tyre =0.4
Solution:
SSD=0.278Vt+〖(0.278V)〗^2/(2g(f±i))=0.278*80*4+〖(0.278*80)〗^2/(2*9.81*(0.4-.06))=163.18≈164 m


Overtaking Sight Distance (OSD)
Factors affecting Overtaking Sight Distance (OSD):
Speed of overtaking vehicle, overtaken vehicle and vehicle coming from opposite direction
Spacing between vehicles
Skill and reaction time of driver
Rate of acceleration of overtaking vehicle
Gradient of road
OSD is the distance that should be open to the vision of the driver in the vehicle intending to overtake a slow moving vehicle ahead with safety against the vehicle coming from opposite direction. This is known as Passing Sight Distance
A= overtaking vehicle with speed v kmph
B= overtaken vehicle with speed speed v-16 kmph
C= opposite vehicle with speed v kmph OSD




d1           s                   b    s          d3
d2
vb= speed of overtaken vehicle, m/s
v= speed of overtaking vehicle, m/s
tr= total reaction time, seconds (2s)
Now, d1= vb*tr
d2= b+2s
spacing 's' of two vehicles moving with the speed vb m/s
empirical relation; s=0.69* vb+6.1, m (or s=0.7vb+6, Khanna and Justo)
b=vb*T; T=time required to complete actual overtaking operation
so, d2= vb*T+2s= vb*T+  1/2*a*T^2
2s=1/2*a*T^2  ⇒T=√(4s/a)
and d3=vc*T; vc= speed of vehicle c, which is also driving in design speed or less
Therefore; OSD=d1+d2+d3
        =vb*tr+ vb*T+2s+vc*T
This is applicable when there is no traffic separator provided on the road
When the opposite vehicle is separated by median strip or traffic separator, OSD=d1+d2


The zones which are meant for overtaking are called overtaking zone
The minimum length of overtaking zone = 3XOSD
The desirable length of overtaking zone = 5Xosd

Problem-1:
The overtaking and overtaken vehicles are 70 and 40 kmph, respectively on a two way traffic road. If the acceleration of overtaking vehicle is 0.99 m/sec/sec.
(a) Calculate the safe overtaking sight distance
(b) Mention the minimum length of overtaking zone
(c) Draw a neat sketch of the overtaking zone and show the positions of the sign posts.
Solution:
Overtaking sight distance for two way traffic;
OSD=d1+d2+d3 = vb*tr+ vb*T+2s+vc*T
Here: Vb=40 kmph=11.111 m/s; tr=2.5 sec Vc= 70 kmph=19.444 m/s
s=0.69* vb+6.1 = 0.698*11.111+6.1 = 13.755 m
. T=√(4s/a)=√((4*13.755)/0.99)=7.455 sec
d1 = vb*tr = 11.111*2.5 = 27.775
d2 =s+ vb*T+s =111*7.455+2*13.755 = 82.83+27.51 = 110.34
d3 = vc*T = 19.444*7.455= 27.51 m
OSD = d1+d2+d3  = 27.775+110.34+144.955 = 283 m
OSD for one way traffic = OSD(1-way) = d1+d2 =27.775+110.340 = 138.115 m
Minimum length of overtaking zone =3*(OSD) =3*283 = 846 m
Desirable length of overtaking zone = 5*(OSD) =5* 283 = 1415 m






Problem:
Calculate safe OSD for a Mahendra Highway for level area. If acceleration of overtaking vehicle is 1 m/sec/sec. Assume all other data suitably
Solution:
Assume;V = Vc = 120 kmph; = 33.333 m/s
Vb = Vc – 16 = 120 – 16 =104 kmph = 28.889 m/s
tr = 2.5 sec;
a=1 m/s/s
s=0.7vb+6 = 29.333 m
T=√(4s/a) = 10.832 sec
d1=vb*t = 83.333 m
d2= vb*T+2s = 419.729 m
d3=vc*T = 312.926
OSD=d1+d2 (1-way) = 530.062 m (take 530 m)
OSD=d1+d2+d3 (2-way) = 922.729 m (take 925 m)




Sight Distance at Intersection:

It is important that on all approaches of intersecting roads, there should be a clear view across the corners from a sufficient distance so as to avoid collision of vehicle. The design of sight distance at intersections may be based on three possible conditions:

Enabling the approaching vehicle to change speed
The sight distance should be sufficient to enable either one or both the approaching vehicles to change speed to avoid collision. The vehicle approaching from the minor road should slow down.

Enabling the approaching vehicle to stop
In this case, the sight distance for the approaching vehicle should be sufficient to bring either one or both of the vehicles to a stop before reaching a point of collision. It is the responsibility of the drives on the minor road who would cross or enter this main road, to stop or change speed to avoid collision. The traffic of the minor road is generally controlled by an appropriate traffic sign. Eg: give way sign.

Enabling the approaching vehicle to cross the main road
This case is applicable when the vehicles entering the intersection from the minor road are controlled by stop sign and so these vehicles have to stop and then proceed to cross the main road. In such a situation, the sight distance available from the stopped position of the minor road should be sufficient to enable the stopped vehicle to start, accelerate and cross the main road, before another vehicle travelling at its design speed on the main road reaches the intersection.

From safety considerations, the sight distance at uncontrolled intersections should therefore fulfill all the above three conditions.

At uncontrolled intersection:
From safety point of view, the sight distance at uncontrolled intersections should therefore fulfill all the above three conditions. The higher of the three valued may be taken at unsignalised intersections at grade, except at rotaries. The sight distance>= SSD.

At rotaries:
At rotaries the sight distance should be at least equal to the sage stopping distance for design speed of rotary.

At signalized intersection
At signalized intersection above three requirements are not applicable.

At Priority Intersection
Where a minor road crosses the major road, the traffic on the minor road may be controlled by stop or give-way sign to give priority to the traffic on the major road. The visibility distance available along the minor road should be sufficient to enable the drivers stop their vehicle.

Sight Triangle:
The area of un-obstructed sight formed by the lines of vision is called the sight triangle.


Set-Back Distance (M)
It is the clearance required to         S
provide adequate set back distance(M) at an intersection
and depends on i) Sight distance (s)
ii) Radius (R)      M
iii) Length of Transition Curve (Lt)
Lc>S, M=S^2/8R                      R     R-M     R
       line of sight
    ii     Lc<S, M=(L(2S-h))/8R


Problem-1:
On a highway there is a horizontal curve of radius 450 m and length of 250 m. Compute the setback distance required from the centre line of the inner side of the curve so as to provide for
SSD of 110 m
Safe OSD of 350 m 250 m
Solution:
Here; R= 450 m
L= 250 m
SSD= 110 m
OSD= 350 m
d= 1.90 m
SSD<L
.α/2=180/π*SSD/2R=〖7.002〗^0
       Setback= m'= R- (R-d)*Cosα/2=450-(450-1.90)*Cos(7.002)=5.24 m
Thus the required clearance from the centre line to provide SSD of 110 m is =5.30 m
OSD>L
.α/2=180/π*L_c/2(R-d) =〖15.97〗^0                .      Setback = m'= R- (R-d) *Cosα/2+(S-L)/2*sin⁡(α/2)=450-(450-1.9)*Cos(15.97)+(350-250)/2*Sin(15.97)
=19.4+13.75=33.15 m
The minimum setback distance required from the centre line of the road on the inner side of the pavement to provide an OSD of 350 m is = 33.15 m






3.4.4 Super-elevation

The outer edge of the pavement is raised with respect to the inner edge in order to provide a transverse slope throughout the length of the curve. This transverse slope is known as superelevation. Superelevation is provided to balance the effect of centrifugal force.
tanθ=NL/ML
e=E/B;because θ is small and tanθ≈θ

Analysis of Superelevation:
The forces acting on the vehicle while moving on a circular radius; R (m) at a speed of v (m/s) are:
Centrifugal force;
p=〖wv〗^2/gR, acting horizontally outward through the CG
Weight of the vehicle, acting vertically downward through the CG
The frictional force developed between the wheels and the pavement counteracting transverse along pavement surface towards the centre of the curve.

P.Sinθ

                                                                P.Cosθ
 
W.Sinθ P
..............N

      f.R1+f.R2          R2
                                      R1 NL
        W
       M                     ..........L
                                                       Radius (R)
  W.Cosθ

For equilibrium:
p Cosθ=w Sinθ+Fa+Fb
p Cosθ=w Sinθ+f(w Cosθ+p Sinθ)        
p(Cosθ-f Sinθ)=w Sinθ+fw Cosθ                                      
Dividing both sides by w.Cosθ        
p/w (1-f Tanθ)=Tanθ+f      
p/w=(Tanθ+f)/(1-f Tanθ)      
For design purpose, f is assumed to be 0.15 and e=0.07 Hence; 1-f.e≈1
p/w=e+f     ........................................... (i)
Also p/w=v^(`2)/gR         ........................................... (ii)
equating (i) and (ii)
e+f=v^2/gR=〖(0.278V〗^()2)/(9.81*R)=V^2/127R
According to NRS;  e+f=V^2/126.5R
Where; e=superelevation
f=design value of lateral friction=0.15
V=speed in kmph
R=Radius of horizontal curve in m
Types of superelevation:
Minimum superelevation;e≤0.07 or 7%
- slope equal to the slope of the CAMBER
- maximum transverse slope required from the drainage point of view 0.5% minimum. normally 3-5%
Maximum superelevation; emax=0.07 or 7%
-In hill roads without snow; e=0.1 has also been taken


Table: Radii beyond which superelevation is not required; (Khanna and Justo page-111)
     Design speed Radius of horizontal curve for camber of
            kmph 4% 3% 2.5% 2% 1.7%
20
25
30
35
40
50
60
80
100

Superelevation Design:
Various steps for Superelevation design are:
In order to overcome the effect of mixed traffic operation, 75% of design speed is taken neglecting f; e=  V^2/225R.
If the calculated e is less than 0.07 (7%), the value obtained is provided. If the valued of e exceeds 0.07, then provide maximum superelevation. i. e. e=0.07 or 7%.
Check the coefficient of friction developed for the maximum value of e=0.07 at the full value of design speed; f=V^2/127R-e (=0.07). If the value is less than 0.15, calculated value is provided. If the value of e exceeds 0.15, given designed speed is reduced.
The allowable speed (Va kmph, or va m/s) at the curve is calculated by considering the design coefficient of lateral friction and the maximum superelevation:
e+f=V^2/127R     e+f = 0.07+ 0.15 = 0.22
Va >V V_a=√(127*0.22R)

Attainment of Superelevation; (Introduction of Superelevation)
,e+f=V^2/127R
           P/w=impact factor; the effect of centrifugal force is minimized by superelevation, e and f.
To cater mixed traffic operation; e=((0.75〖V)〗^2)/127R=V^2/225R
Only 75% of designed speed is considered in IS. But in BS 67% of speed is in practice.

In order to obtain a full value of superelevation: (DESCRIBE YOURSELF)
elimination of the crown of the cambered section (Minimum Superelevation)
shifting of crown outward
rotation of outer edge about the crown
introduction of full value of superelevation throughout the length of circular curve (Maximum Superelevation)
Full value of superelevation can be achieved by any of the following ways:
Rotation of the pavement about the centerline (CL)
Rotation about the inner edge
Rotation about the outer edge
When the radius of circular curve is large, no transition curve is required. In such case 60-80% of superelevation is achieved in the tangent part.


shifting of crown outward


rotation of outer edge about the crown

Problem 1:
The radius of a horizontal curve is 100 m. The design speed is 50 kmph and the designed coefficient of lateral friction is 0.15
Calculate the superelevation required if full lateral friction is assumed to be developed.
Calculate the coefficient of friction needed if no superelevation is provided.
Calculate the equilibrium superelevation if the pressure on the inner and outer wheels should be equal.
Solution:
e+f=V^2/127R
.e+0.15=〖50〗^2/(127*100)  ⇒e=0.0468≈4.7% {<7% i.e.OK}
e+f=V^2/127R
. e=0 ⇒ f=V^2/127R=(50*50)/(127*100)=0.197{>0.15,not ok,f≤0.15}

we should adopt f=0.15, which is the maximum permissible value

To balance the pressure on the both wheels,f=0
. e=V^2/127R=〖50〗^2/(127*100)=0.197

for mix traffic operation,
Vdesign = 0.75*Vgiven
so. e=((0.75〖)V〗^2)/gR=V^2/225R=0.111  {  f≤0.15 i.e.OK…..neglecting f }

Problem-2:
Design the rate of superelevation; given the radius of horizontal curve 500m and designed speed 100kmph.
Solution:
For mixed traffic conditions, superelevation is given by
e=((0.75〖)V〗^2)/gR=V^2/225R=〖100〗^2/(225*500)=0.089  e>0.07 i.e.not OK the limit of e=0.07
Check for coefficient of lateral friction; f
e+f=V^2/127R  or 0.07+f=〖100〗^2/(127*500)  ⇒f=0.1575-0.07=0.0875 {f<0.15 i.e.OK}
Hence the design value for superelevation is e=0.07 with f<0.15....................OK...............

Problem-3
Design the rate of superelevation; given the radius of horizontal curve 200m and designed speed 80kmph. Calculate the restricted limit of speed if required.
Solution:
For mixed traffic conditions, superelevation is given by
e=((0.75〖)V〗^2)/gR=V^2/225R=〖80〗^2/(225*200)=0.142  {e>0.07 i.e.not OK;use e=0.07}

Check for coefficient of lateral friction; f
e+f=V^2/127R  or 0.07+f=〖80〗^2/(127*200)  ⇒f=0.252-0.07=0.182 {>0.15 i.e.not OK;use f=0.15}

Calculation of restricted speed;
e+f=V^2/127R  or 0.07+0.15= V^2/(127*200)  ⇒V=√(0.22*127*200)=74.75 kmph

Hence the design value for superelevation is e=0.07 with f=0.15 and speed restricted to 75 kmph. As far as possible design speed should not be reduced. The re-design of the alignment is suggested if possible.

3.4.5 Extra-widening At The Curved Path

we= wm +wpsh ; mechanical widening and psychological widening
.W_e=(nl^2)/2R+V/9.5R

It is the additional width required of the carriageway that is required on a curved path than the width required on the straight path.

Reasons:
Rigidity of the wheel base
Preferential use of the outer lane
More clearance between opposing vehicles
Difference in slip angles
Rear wheels go out while the front wheels are within the pavement
Visibility is enhanced when the vehicle moves along the outer lane

Mechanical Widening:


          B                        l R2
      C  A             R1           O R1    R2    R3 R1<R2<R3

R1=Radius of the path travelled by the outer rear wheel (in m) R2=Radius of the path travelled by the outer front wheel (in m)
R3=Off tracking or mechanical widening (in m)

In ∆AOB,     <A=90^0
OB2=AB2+OA2
OA2=OB2-AB2
R12=R22-L2
(R2-wm)2= R22-L2
R22 -2 R2 wm + wm2= R22-L2 ; wm=OC-OA=OB-OA= R2 - R1
l2=wm(2R2-wm)
w_m=l^2/(2R_2-w_m )≈l^2/2R  (Approx), This is for single lane pavement.
For a road having 'n' traffic lanes w_m=(nl^2)/2R

Method of introducing extrawidening
widening on the inner edge of the curve with transition path
ideally 'ew/2' on inner edge and 'ew/2' on outer edge
on sharp curves of hill roads, full value of 'ew' may be provided on the inner/outer edge

Problem-1:
Calculate the extrawidening required for the pavement of width 7.0 m on a horizontal curve of radius 250 m if the longest wheel base of vehicle expected on the road is 7.0 m. Given design speed =70 kmph.
Solution:
Extrawidening is given by:
we= wm +wpsh =(nl^2)/2R+V/(9.5√R);    Here; n=2; l=7.0; R=250 m; V=70 kmph
.=(2*7^2)/(2*250)+70/(9.5*√250)=0.196+0.466=0.662 m
Problem-2:
Find the total width of pavement on a horizontal curve for a new national highway to be aligned a rolling terrain with a ruling minimum radius. Assume necessary data.
Solution:
Assume the following data: (NRS_2045)
National highway on rolling terrain, ruling design speed = V = 80 kmph (clause
Normal pavement width = W = 7.0 m (clause-3.2)
No of lane = n = 2
Wheel base of truck = l = 6.0 m
Maximum value of superelevation and skid resistance; e =< 0.07 and f =< 0.15
Then;
e+f=V^2/127R  or 0.07+0.015= 〖80〗^2/(127*R)  ⇒R=229.06 m ≈230 m
we= wm +wpsh = (nl^2)/2R+V/(9.5√R)=(2*6^2)/(2*230)+80/(9.5*√230)=0.157+0.555=0.712 m
Total width of pavement = 7.0 + 0.712 =7.712 m


3.4.6 TRANSITION CURVE: Definition, Types and Design

Definition and Types of Transition Curve:
Transition curve may be defined as a curve of varying radius ( R c ≤R_T≤∞) between straight and circular path in order that the application of centrifugal force would be gradual.
Objectives:
to introduce centrifugal force gradually in order to avoid a sudden jerk or discomfort to the passengers.
to introduce superelevation at a desirable rate
to enable the driver to turn his vehicle slowly and comfortably.
to introduce extrawidening at the desirable rate.
to fit the road alignment in a given topography and also to improve the appearance of road.

Types of Transition Curve:
Spiral or clothoid
Bernolli's leminscate or lemniscate
Cubic parabola










Fig: Spiral Fig: Lemniscate








Fig: Cubic Parabola Fig: Cubic Parabola

Design of Transition Curve (Length Calculation)
By the rate of change of centrifugal acceleration
By the introduction of superelevation
Condition-1
P=(mv^2)/R   ........................ (i)
P=ma   ........................ (ii)
Hence a=v^2/R;where R=Radius of circular curve
Rate of change of centrifugal acceleration, I (m/s3)
I=a/t=(v^2/R)/t=v^2/(R.t)    ⇒t=v^2/RI…………………..(iii)
where t is the time taken by the vehicle to travel a transition path; Lt. If the vehicle is assumed to travel the distance Lt with a uniform speed, v (design speed, m/s)  then
Lt= v*t  ⇒t=Lt/v  .............................................. (iv)
equating  (iii) and (iv), we get
Lt= =v^3/RI  =((0.278〖v)〗^3)/RI=v^3/(46.5*RI)  ⇒  v^3/(46.5*R〖*I〗_max ).
Condition-2
60-80% of superelevation is achieved in the runoff length or a minimum of 2/3 of the SE is obtained in the tangent path.
Let the change of introducing SE be 1:N and N=150-60
From ΔABC,tanθ= H/W
or H=ew ………………………..(i)
From   ΔBCD,tanα= H/Lt or 1/N=H/Lt
  ⇒H=Lt/N………………………………(ii)             St. line Equating (i) and (ii)
.e w=Lt/N or Lt=N e w ;
where w is the width of c/w including extra-widening
w=ws+we and we=wm +wpsh ; mechanical widening and psychological widening
we =(nl^2)/2R+V/9.5R
This is applicable when the SE is achieved by rotating the pavement about inner edge or outer edge.
If the pavement is rotated about CL; Lt=new/2

Condition-3; Empirical Formula (IRC)
For plain and rolling terrain; Lt=(2.7*V^2)/R For mountainous and steep terrain, Lt=V^2/R
Accept the value which is the greatest of there...........................................................................

Problem-1:
Calculate the length of transition curve and the shift using the following data:
Design speed = 65 kmph
Radius of circular curve = 220 m
Allowable rate of superelevation (pavement rotated about centre line) =1 in 50
Pavement width including extrawidening = 7.5 m
Solution:
Length of transition as per allowable rate of centrifugal acceleration:
Allowable rate of centrifugal acceleration: I=80/(75+V)=80/(75+65)=0.57 m⁄s^2
This value is between 0.5 and 0.8 and hence accepted;
Then L_s=(0.0215V^3)/CR=(0.0215〖*65〗^3)/(0.57*220)=47.1 m

Length of transition as per allowable rate of introduction of superelevation E:
Allowable rate of superelevation;
.e=V^2/225R=〖65〗^2/(225*220)=0.085 {>0.07(allowable) hence adopt only 0.07})
f=V^2/127R-e=〖65〗^2/(127*220)-0.07=0.081 {<0.15(allowable) hence e=0.07 is ok})
Then, Ls=(Ne(W+We))/2=(150*0.07*7.5)/2=39.375 m
Length of transition as per Empirical Formula (IRC):
.Ls=(2.7*V^2)/R=(2.7*〖65〗^2)/220=51.85 m
Conclusion:
Adopt Highest Value = 51.8≈52 m
Shift; S=L^2/(24*R)=(52*52)/(24*220)=0.51 m
3.5 ELEMENTS OF VERTICAL CURVE
3.5.1 Definition and Types of Gradient:
Gradient shall be defined as the slope of the inclined line or surface. Gradient shall be expressed as one of the following ways:
. in percentage; example 10%,20%, 33% etc (n%)
10% means the rise/fall of 10 units per 100 units of horizontal distance travel
. in fraction; example 1in 40, 1 in 200, 1 in 2000 etc. (1 in N)
1 in 40 means the 1 unit of rise/fall (vertical dist.) per 40 units of horizontal dist. travel.
. tanθ ≈ θ, as θ is small
Based on Geometry Gradient shall be of following two types
Rising Gradient
If the slope of a line/ground increases along the direction of progress, it is said to be rising gradient.
Falling Gradient
If the slope of a line/gradient decreases along the direction of progress, it is said to be falling gradient.


1 in 40
10%



Rising Gradient (b) Falling Gradient
Based on Function, Gradient shall be of following 5 types
Ruling gradient:
It is the maximum gradient within which the designer attempts to design the vertical profile of a road. It is also known as design gradient since under normal condition filling and cutting are balanced. As per IRC the recommended value of ruling gradient is 1 in 30, 1 in 20 and 1 in 16.7 in plane/rolling, mountainous and steep terrain.
Limiting gradient
Whenever the topography of a place has steeper gradients then we provide limiting gradient which is more than ruling gradient. But the length of limiting gradient is limited considering safety. The limiting gradient is broken either by providing a level road or road with a ease gradient. As per IRC the recommended value of limiting gradient is 1 in 20, 1 in 17.7 and 1 in 14.3 in plain/rolling, mountainous and steep terrain respectively.
Exceptional gradient
In some cases its quite impossible to provide ruling/limiting gradient. Under this condition exceptional gradient is provided. The length of exceptional gradient is as less as possible. As per IRC the recommended value of exceptional gradient is 1 in 15, 1 in 14.3 & 1 in 12.5 in plain/rolling, mountainous and steep slope.

Minimum gradient
A minimum value of gradient is also required along the direction of the road because of the drainage purpose. As per IRC the minimum gradient of 0.5% to 1.0% should be provided considering various situation.
Floating gradient
It is the type of gradient in which the frictional resistance between the tyre of vehicle and road equal to zero. It means vehicle move on the road even under off condition.
Average gradient
It is the average of different gradient between two points on the road. The numerical value of average gradient may be +ve, - ve or zero.

3.5.2 Momentum Grade


3.5.3 Grade Compensation

The reduction in grade due to the horizontal curve associated with gradient is termed as grade compensation,
Grade compensation= (30+R)/R  ⇒Maximum vaue=75/R
Compensation is not required when the grade is flatter that 4%

Problem:
If gradient =6%, R=75 m; how much compensation is preferred in this curve?
Solution:
grade compensation= (30+R )/R=(30+75)/75=1.4  and  75/R=75/75=1
the optimum value for grade compensations = 1%.

3.5.1 Definition and Types of Vertical Curve

These are the curves provided in vertical alignment at each point of vertical intersection (PVI) in order that the change in grade was gradual.
Necessity:
to obtain adequate visibility and safe driving
to secure comfort to the passengers

Types:
Vertical Summit Curve
Vertical Valley Curve


3.5.2 Design of Vertical Summit Curve

convexity upward or concavity downward
Design control based on visibility criteria
night driving
day time

y=ax^2; ⇒y=x^2/C  ⇒C=x^2/y
Stopping Sight Distance: (SSD)
L>SSD
L=(NS^2)/〖(√2H+√2h)〗^2 =  (NS^2)/4.4;
where we are assuming H= driver's eye height above road surface= 1.2 m
h= height of the object = 0.15 m

L<SSD
L= 2S -  〖(√2H+√2h)〗^2/(NS^2 )=2S-4.4/N

Overtaking Sight Distance (OSD) or Intermediate Sight Distance (ISD)
L>SSD
L=  (NS^2)/8H=(NS^2)/9.6
L<SSD
L=2S-8H/N=2S-9.6/N

3.5.3 Design of Vertical Valley Curve

Valley Curve or Sag Curve:  (Convexity downward or Concavity upward)
Design control of valley curve (criteria)
Comfort condition
Head light sight distance – night driving
A transition curve of a cubic parabola is introduced in a sag curve
y=x^3/b  where b=3/2*L^2/N R=L/2N; N=N1+N2= in radian
or  y=bx^3  where b=2N/(3L^(2 ) )
Comfort Condition
Lt,min= v^3/(RI_max )=v^3/RC
Impact factor; Imax=1.59*(NV^2)/L  ≤17%
Value of R (at Lt)=L_t/N=L/2N
L_t/N=L/2N
L_t=v^3/(RL_t )*N⇒⇒L_t=√((Nv^3)/C).
〖L=2*L〗_t=2*√((Nv^3)/C).
 where, C= allowable rate of change of centrifugal acceleration = 0.6 m/s3
 L_t=0.38*√(Nv^3 )
Head light sight distance
L>S
,L=(NS^2)/(2H_1+2S*tanα)=(NS^2)/(1.5+0.035*S)

L<S
,L=2S-(1.5+0.035*S)/N=
where h1=0.75= vehicle headlight height from road surface
,S=Headlight sight distance
    ,=Minimum stopping sight distance

Lowest point on valley curve is to be known highest point of summit curve is also to be known visibility on summit curve can be disturbed due to humps on road surface over summit curve.

3.5.4 Lowest point of Valley  Curve and Highest point of Summit Curve
Let H be the highest point on the summit curve which occurs at a horizontal distance x0 from the tangent point T1.
The equation of the curve, y=x^2/C
EH=y0=  〖x_0〗^2/C
Also, EQ= n1x0
y=HQ= EQ-EH=n1 x0 -   〖x_0〗^2/C
If H is the highest point then x is maximum, dy/dx=0

or n1  -   (2x_0)/C=0 ⇒C=(2x_0)/n_1  ........................................... (i)
also     C=2L/n=2L/(n1+n2 ) ......................................................... (ii)
Equating (i) and (ii)
(2x_0)/n_1 =2L/(n1+n2 )  ⇒⇒⇒⇒x_0= nL/(n1+n2 )



3.5.7.2 Lowest Point on the Valley Curve:


Let L be the lowest point on the valley curve which occurs at a horizontal distance x1 from the tangent point T1.
The equation of the curve, y=x^3/b
EH= y= x^3/b
In fig:          y1= QL=QS-LS =n2 x1 -   〖x_1〗^2/b
Now L will be the lowest point on the valley curve when y1 is maximum, (dy_1)/(dx_1 )=0
or n_2- (3〖x_1〗^2)/b=0 ⇒x_1=√((n_2 b)/3)........................ (i)
also     b=(3L^2)/(2n ) ......................................................... (ii)
Equating (i) and (ii)
= ⇒⇒⇒⇒x_1= (n_2 L^2)/(2(n1+n2) )


Problem-1:
A vertical summit curve is formed at the intersection of two gradients +3.5% and -5.5%. Design the length of summit curve to provide SSD for designed speed 85 kmph.
Solution:
Given designed speed = 85 kmph
Gradients +3.5% and -5.5%
Assume t=2.5 sec
f=0.4 (surface resistance)
(i) Stopping Sight Distance (SSD); SSD=0.274*t*V+V^2/(254*f)
As there is ascending gradient on one side of the summit and descending gradient on the other side, the effect of gradients on SSD is assumed to get compensated and hence ignored.
SSD=0.274*2.5*85+〖85〗^2/(254*0.4)=59.05+71.1=130.15 m ≈130 m (say)
(ii) Deviation Angle; N=0.035 – (- 0.055) = 0.090
Assuming L greater than SSD, then from standard equation
L=(N*S^2)/4.4=(0.09*〖130〗^2)/4.4=345.6 m
Here L>S;
Thus the length of summit curve = 345.6 m ≈346 m

Problem-2:
An ascending gradient of 1 in 100 meets a descending gradient of 1 in 125 m. Design the summit curve for a speed of 85 kmph to have an OSD of 475 m.
Solution:
Given; Ascending gradient = + 0.01
Descending gradient = - 0.008
Deviation angle = 0.01-(-0.008) =0.018
Assume; L>S..........................
Then, L=(N*S^2)/9.6=(0.018*〖475〗^2)/9.6=423.1 m <475 m (OSD)
  i.e. L<S hence the assumptions is wrong
Again assume L<S
Then, L=2S-9.6/N=2*423.1-9.6/0.018=950-433.4=416.67 m≈417 m
i.e. L<S hence the assumptions is right
Hence the length of summit curve should be adopted as 417 m

Problem-3:
A vertical curve is to be designed when two grades of +1/150 and -1/85 meet on a highway. The SSD and OSD are required 190 and 650 m respectively. But due to site condition the length of vertical curve has to be restricted to 520 m if possible. Calculate the length of the summit curve needed to fulfill the requirements of (i) SSD (ii) OSD or at least ISD and discuss the result.................ans=478 m taking ISD
Solution:
Deviation Angle: n=n1+n2 = +1/50 – (-1/85) =27/850
Problem- 4:
A valley curve is formed by descending grade of 1 in 30 meeting an ascending grade of 1 in 40. Design the length of vertical curve to fulfill the following conditions.
Comfort Condition
Head light sight distance requirements for a design speed of 85 kmph.
The allowable rate of change of centrifugal acceleration may be assumed as C=0.6 m/sec2
Solution:
Deviation angle; N=-1/30-1/40=-7/120
Velocity in m/s; v=85/3.6 = 23.6 m/s
For comfort condition;
. L=2((Nv^3)/C)^(1/2)=2(7/120*〖23.6〗^3/0.6)^(1/2)=2*35.75=71.50 m

Head light sight distance;
Neglecting the descending and ascending gradients at the valley curve, the value of SSD=vt+v^2/2gf
SSD=23.6*(t=2.5)+〖23.6〗^2/(2*(g=9.81)*(f=0.35) )=59.0+81.11=140.11 m
Assuming L>SSD; then
L=〖N*S〗^2/((1.5+0.035S) )=-7/120*〖140.11〗^2/((1.5+0.035*140.11) )=178.9 m≈179 m
As the value of L is more than SSD, The assumption is correct. The valley curve length based on head light sight distance being higher than that based on comfort condition. Hence the designed length of valley curve is 179 m or say 180 m.



4.0 HIGHWAY DRAINAGE SYSTEM
4.1 INTRODUCTION
All highways are constructed on soil which is composed of different layers. Pavement rests on sub grade. Serviceability of highway depends upon the moisture and measures for controlling the moisture. Road are constructed either by cutting or embankment depending upon vertical profile of designed alignment with respect to original ground level which are exposed to the action of rain and sun. Hence stability of road depends upon water content in soil.
4.1.1 Highway Drainage System: An Introduction
It is the process of removing and controlling excess surface and sub surface within right of way. It includes interception and diversion of water from road surface and sub grade. The installation of suitable surface and sub surface drainage system is essential in highway design and construction.

Removal and diversion of surface water is surface drainage. It is removed laterally by providing camber or cross fall. Removal and diversion of surface water from roadway and adjoining land is sub-surface drainage.
Requirement of Highway Drainage System
Surface water from carriage way and shoulder should be effectively drained off laterally without allowing it to sub grade.
The surface water from adjoining land should be prevented from entering the roadway.
Side drain (Longitudinal Drain) should be of sufficient capacity and slope to carry all surface water collected.
Flow of surface water across road and shoulders and along slopes should not cause erosion.
Highest level of Ground Water Table should be kept well below the level of sub grade (at least 1.2 m)
In water logged areas special precautions should be taken.
4.1.2 Highway Drainage System: Importance
Variation or increase in moisture content decreases the strength or stability of soil mass. Highway Drainage is important because:
Excess moisture in soil sub grade causes considerable lowering in its stability. The pavement is likely to fail due to sub grade failure.
Increase in moisture content causes reduction in strength in of many pavement materials like stabilized soil and Water Bound Macadam.
In clayey soil variation of moisture content causes considerable variation in volume of sub grade which may leads to pavement failure.
Formation of waves and corrugations in flexible pavement is due to poor drainage.
Sustained contact of water with bituminous pavement causes failure due to stripping of bitumen from aggregates like loosening or detachment of some of the bituminous pavement layers and formation of pot holes.
The prime cause of failure in rigid pavement by mud pumping is due to presence of water in fine sub grade soil.
Excess moisture causes increase in weight and thus increase in strength of soil mass. This is one if the main reason of failure of earth slope and embankment foundation.
In places of freezing temperature, presence of water in sub grade soil causes damage due to frost action.
Erosion of soil from top of un-surfaced road and slope of embankment, cut and hillside is due to the surface water.

4.2 Causes of Moisture Variation in Subgrade Soil:
Planning and design of measures for the removal of excess of water from highway vicinity and control of moisture in subgrade soil essentially requires that the various sources of water to and loss of water from subgrade be identified or established first. For example, the water already seeped below the ground surface cannot be disposed by providing surface channel or a culvert. Similarly, if the sources of water is the rain storm, surface water from the road surface and back slope during rain should be drained towards the natural drainage ways by means of providing road side channels.
Proper identification of sources contributing to excessive moisture to subgrade leads to the design of drainage system i. e. safe, efficient and economical. We are here just interested to identify the various sources of water to and losses from subgrade (not for design point of view). This may be conveniently expressed by the water balanced equation as given below:
W= (A+B+C) – (D+E+F)
Where, W= water contained in subgrade soil at any time of the year
A= amount of water infiltration into subgrade soil due to rainfall
B= amount of water seeping towards subgrade from adjacent higher ground
C= amount of water coming to the subgrade due to:
.i. capillary rise
.ii. upward movement of water table
.iii. transfer of water vapor due to difference in temperature between upper and lower soil subgrade layer
D= loss of water from subgrade due to flow away towards lower adjacent ground
E= loss of water due to evaporation, transpiration etc.
F= loss of water due to percolation downward.

……rainfall ….rainfall….rainfall……

Fig:- Causes and Sources of Moisture Variation in Subgrade

Components/Classification of Highway Drainage System:
Depending upon the nature of sources of water by which the subgrade soil could be saturated and methods of disposing such water; a highway drainage system may be classified into two broad groups:
Surface drainage system
Longitudinal drain system
Cross-drainage works
Erosion control mechanism
Energy dissipating structures
Subsurface drainage system
Drainage of infiltrated water
Control of seepage flow
Lowering water table
Control of capillary rise



4.3 Surface Drainage System:
The surface water is to be collected and disposed off. It is collected in side drain and disposed off at nearest stream, valley or water course. Cross drainage structures like culverts and small bridge may be necessary for disposal of surface water from road side drain. Surface drainage system consists of longitudinal drain, transverse drain and energy dissipating structure.
4.3.1 Longitudinal drain:
The water from pavement surface is removed by providing camber or cross slope to the pavement. The rate of cross slope is decided based on type of pavement surface and rainfall. In rural highway, water drained from pavement surface has also to drain across the shoulders before it leads to side drain. Hence shoulders of these roads are constructed with suitable cross slope. But in urban roads due to limitation of land width, covered longitudinal drain are provided.

Different types of Longitudinal Drains based on their Shape
The function of roadside drains is to collect water that has fallen on the carriageway and the batters of cutting s or embankments to direct to edge of the formation. Roadside drains are used along the road edge and can also cater for the drainage of the abutting developed area. The most common types of roadside drains are detailed are explained below:




Different types of Roadside Drains based on their Functions (used in Hill and Rural Roads):

Embankment toe drains:
The function of embankment toe drains are to collect water that has fallen on the carriageway and the batters of cuttings or embankments to direct to edge of the formation. Toe drains are used at the base of embankments wherever the road is in a fill section. Generally, the gradient follows that of road and is usually shallow shince cathcment area is restricted to the roadway and the cut slope.
Shoulder Drains
Shoulder drains are used along the shoulder. The function of shoulder drain is to prevent water from infiltrating the road surface and carry water away from roadway. Because shoulder, toe and roadside drains are often built on flat grades to match road grade, they must either have large cross-section area or have frequent discharge point. Depending upon the nature of material in which they are constructed and their longitudinal grade, the shoulder, toe and roadside drains may be lined with stone, concrete or a bitumen seal to resist the action of scouring.
Interceptor Drain
Interceptor drains are located along the uppermost edge of cut slopes where the cutting begins, and along the edge of the cut slope descending towards the lowest point of the natural watercourse. Due to the position of the interceptor drain, it must be sufficiently large to account for siltation and debris collection. Types of interceptor drains to be used depend upon type of geographic features and design flow volume. The use of precast block section for interceptor drains should be discouraged because of possible seepage problem.
Bench or Berm (earthen embankment) Drain
Bench drains are placed longitudinally along the bench of a cut section and Berm drains are located on the berm of a fill section to intersect water running down the slope. Each bench or berm drain should catch rainwater falling on the slope immediately above. Bench or berm drains are provided on each bench or berm on the inner edge of the cut and the embankment slope respectively. Benches and berms are usually provided at 6 m height intervals and are generally shallow with their gradients following the bench and berm gradients.
Median Drains
Median drains normally are required in multiple-lane divided highways. Median drains are generally a shallow depressed area, and at intervals the water is intercepted by transverse channels that discharge into a sewer or storm drain. The function of median drain is to collect surface water which runs towards the central median and are generally of small section and gentle gradient. Median drains are particularly used both in urban and rural roads of high geometric design standards.
Outfall(fill) and Cascade(cut) drain
Outfall (fill) and Cascading (Cut) drains are between the shoulder drain and bench or berm drain and the interceptor drain. Outfall drains are provided at the lowest point of a sag curve to cater for water flowing along the roadside and shoulder drains. Cascading or outfall also cater for natural drainage path that is cut off on top of cut or fill section. Outfall drains are necessary where culvert under road is discharging on the fill slope. Cascade and outfall drains should be provided with sufficient depth of side slope to prevent splashing over of run-off, which can cause scouring or erosion of grassed slopes.


Drains in Urban Street:
In urban roads, because of the limitations of land width and also due to the presence of the foot path, dividing island and other road facilities, it is necessary to provide underground longitudinal drains. Water drained from the pavement surface can be carried forward in the longitudinal direction between the kerb and the pavement for short distance. This water can be collected in catch pits as suitable intervals and lead through underground drainage pipes.
4.3.2 Cross- Drainage Structure
Whenever streams have to cross the roadway, the structures provided to cross the roadway is known as cross-drainage structures. Also often the water from side drain is taken across by these structures in order to divert the water away from road to a water course or valley.
Some of the important cross-drainage structures are:
Causeway: When flow of water is not only temporary but also about or slightly below the level of road, causeways are provided. A causeway does not restrict the waterway and is constructed perpendicular to the direction of flow. Total period of interruption to traffic has however to be kept as low as possible, not exceeding about 15 days/year.
Culvert: According to Nepal Bridge Standard 2067, the drainage structures having span length up to 6 meters is called culvert. If the span is greater than 6 meters then it is bridge. A culvert is a close conduit placed under embankment to carry across the roadway. The common types of culvert are slab culvert, box culvert, arch culvert and pipe culvert. Choice of culvert on particular site depends upon cost of construction and availability of materials and labours.
In slab culvert, RCC slab is placed over abutments made of masonry and span is limited to 3 meters.
Box Culvert is square or rectangular shape made of RCC. It is used in place of high debris and discharge.
Arch culvert is generally built using bricks and stone masonry and used when depth of embankment is high.
Pipe culvert of minimum diameter 75 cm and made of steel or prefabricated RCC, and is used when discharge is low.

Hydraulic Design of Culvert:
The principle aim in the design of a culvert is to provide a most economical design, within specific limit of headwater elevation and velocity in passing the flow from one end of the culvert to the other.
In hydraulic of the culvert it is necessary to consider first of all the stream channel. The primary control is the permissible elevation of water up-stream of the structure at the inlet, i.e. head elevation. Thus it is essential to determine the relationship between headwater elevation and discharge. This depends upon the manner in which the culvert operates.
Hydraulic classification of culvert on the basis of nature of flow:
1. Culvert with free flow
2. Culvert with part full flow
3. Culvert with full flow
Culvert with Free Flow:
. Non pressure culverts
. H =< 1.2 h¬b
Where, H = headwater depth and h¬b = height of culvert barrel
. Flow is similar to flow through weir
. Majority of culverts are designed to achieve such type of flow

. Full at inlet point and free surface at the entire length of barrel
. H > 1.2 h¬b
. Difficult to achieve in actual field condition s due to the requirements of low headwater depth, tail water depth and adequate slope.


3. Aqueduct: An aqueduct is an open or closed conduit, depending upon nature of water, sufficiently above the roadway provided to drain water across road. The normal position of placing of aqueduct in roadway is cutting. If a road is in cutting exceeding 5 meters and the water either of natural drainage course or irrigation canal has to be drained or taken to irrigate the land, aqueduct is best.
 
Inverted Siphon:  A pressure pipeline crossing a depression or passing under highway is called inverted siphon.

Figure: Aqueduct and Inverted Siphon
Scupper: It is the cheapest type of culvert, used to decrease per km cost of road in low cost pavement. It is of 0.9 to 1.0 meter wide.
4.3.3 Erosion control and Energy Dissipating Structures
4.3.3.1 Erosion Control:
Water emerging out of culverts and other cross drainage structures will have higher velocity than non-scouring velocity for the soil around it. Also the construction of highway bring damage in natural stream bed, existing stable hill slopes and involves the removal of top vegetation covers. So erosion control measures have to be adopted.
The erosion depends upon several factors such as intensity and duration of rainfall, type and condition of soil, height and angle of slope and climatic condition. Some of the erosion control measures are:
Lining of drains: If the mean velocity exceeds the permissible velocity for particular type of soil, the road drain should be protected against scouring. The slope of drain is lined with turf and bottom is covered by cobbles and gravels of desired size. Grass lining are valuable where grass can be supported. For higher velocity type of lining should be stone masonry or brick masonry throughout the perimeter and length of drain. Pre-cast concrete blocks can be used if local stone materials are not available.
Vegetation: It is the process of application of grass on top surface of exposed soil. Soil erosion control is improved by allowing vegetation to grow in fill slope or shoulder portion. Bio-Engineering is other alternative which has proved more effective with sustainable development of age.
Stone pitching, lining and protection works: Due to various reasons slope of cut and fill should be provided higher than angle of repose of soil. In such cases various types of slope protection works are provided.
 
4.3.3.2 Energy Dissipating Structures
Due to higher kinetic energy of water, it causes erosion of soil. So the use of energy dissipating structures is to dissipate the energy of flowing water before letting out on the natural bed so that velocity at that point will be less than eroding velocity.
Some of the important Energy Dissipating Structures are:
Road Rapid: Road channels having bed slopes generally higher than the critical slope are rapids. It is provided at the end of the catch drain.
Ditch Check: In case of large rapid slope, the flowing water has high energy having capacity to erode the bed and side slope of drain. The energy of flowing water can be reduced by providing falls at certain interval. This type of structure is called ditch checks.



Fall or Drop structure: In the design of road drainage system in hill road, it is often necessary to provide drop structures. Such structures are provided frequently in hill roads where the bed slope of existing drainage is high.







4.4 Subsurface Drainage
Stability and strength of road surface depends upon strength of sub-grade which is the foundation layer of road whose strength depends upon its moisture content. Variations of moisture content of sub-grade are caused by:
Penetration of moisture through the pavement surface.
Percolation of water from shoulder, pavement edges and formation slopes.
Rise or fall of underground water table.
Capillary rise of moisture in soil.
Transfer of moisture vapour through soil
Sub-surface drainage is the preventive measure to control excessive moisture in sub-grade soil and various pavements layers. In the case of sub-surface of road, every effort should be made to reduce the change or variation in moisture content to minimum. By the provision of sub-surface drainage, only gravitational water can be drained off and vapour water, capillary water cannot be drained off by this system.
4.4.1 Drainage of Infiltrated Water
During rainy season and snow melting season water will find its way to subgrade soil through permeable surface of adjoining land, shoulder, side slope and cracks on the pavement structure. Removal of such infiltrated water from the subgrade may be accomplished by the arrangement shown in figure 4.38.
The water infiltrated through pavement and shoulder was collected at the side drain with the function of sand blanket. The water infiltrated from side drain were collected in perforated pipe located just below the side drain. The water thus collected was then disposed off with the help of cross-drainage structure.

4.4.2 Control of Seepage Flow
When surface of ground and the impervious layer embedded below it are sloping towards the road, the seepage is likely to occur and reach road sub-grade to effect its strength characteristics. Seepage is likely to occur in hilly region or roads in cutting. If the seepage level reaches the road sub-grade, it should be intercepted to keep the seepage line at safe depth below the road sub-grade as shown in figure 11.7;

4.4.3 Lowering of Water Table
If the ground water table is more than 1.5 meter below the sub-grade of road, it does not require any sub-surface drainage. In the places where the water table is high, the best remedy is to take the formation of embankment of height not less than 1.2 m. If it is not possible to increase the height of formation, deep side trenches should be constructed on both sides of the roads to lower the water level. These trenches are provided with drain pipes and filled at top by filter sand parallel to the road at a slope of 0.5% to 1% as shown in figure 11.5;
If the soil is relatively less permeable, it is possible to lower the high water table by construction of transverse drain, along with longitudinal drain. Transverse drain may be pipe drain or trapezoidal trench drain filled with stone. Stones filled in transverse drain are also called French or Blind drains. The diameter of lateral pipe may be 10 cm and that of longitudinal drain 20 cm or even more according to the requirements.
4.4.4 Control of Capillary rise
Capillary rise is the process of rising water in on sub-grade level or above which depends upon the permeability of soil (high for fine grained soil). If capillary rising is likely to the strength of sub-grade, steps should be taken to arrest the capillary rise of water which is called cutoff. Capillary cutoffs can be of following three types:
.i. Provision of granular layer of suitable thickness or of sand blanket.
During construction of embankment it is provided between sub-grade and highest level of Ground Water Table. Thickness of this granular layer should be such that capillary rise of water remains within this layer.


.ii. Provision of Impermeable Layer of Bituminous layer
Here bituminous material is inserted to arrest the capillary rise. 50% of straight run bitumen of 80/100 grade and 50% of diesel oil at the rate of 1 kg/m2 is used for this layer.

.iii. Heavy duty Tar felt, polythene envelop sheet and other measures can be adopted


4.4.5 Procedures for Drainage Design
Refer book, not in new syllabus, was include in old syllabus















5.0 HILL ROADS
5.1 Introduction
Roads lying in hill or mountain is called hill road. According to Nepal Road Standard 2045, terrain are classified as percent cross-slope as;
Type of Terrain Percent Cross-Slope
Level 0-10
Rolling      >10 -25
Mountainous >25-60
Steep >60
Nepal has a total area of 1, 47,181 km2 of which 66% is covered with hills, mountains and Himalayas. More than 90% of the population living in hills and mountains depends upon the agro-product of the region which is not sufficient. Due to mountainous terrain, waterways and railways are not possible. Even air traffic is difficult due to prohibitive cost of construction and high operating cost.
A hill road is defined as the one, which passes through a cross-slope of 25% or more i.e. mountainous or steep terrain. Through knowledge of geology is must to decide hill road alignment. Prevention of soil erosion and stabilization of hill slopes are the major problems in the maintenance of hill roads. Massive and costly protective works are needed. The climatic condition (Amount and pattern of rainfall, heavy wind, snow problem etc) has to be considered. Also a large number of streams cross the road and hence large numbers of cross drainage structures are needed.
Special Considerations in Hill Road Design
Design of hill roads requires special skill and consideration owing to the problems outlined in the preceding section. These are discussed in brief in subsequent sections under the following headings:
Route location and alignment survey
Geometric design of hill roads
Typical cross-section of hill roads
Special structures in hill roads
5.2.1 Alignment Selection in Hill Road
The selection of alignment in hilly region is a complex problem. The main target of designer is to search the shortest possible short route. Following points are considered in alignment selection.
General Consideration: A hilly area is characterized by a highly broken relief with widely differencing elevations, steep slopes, repeated turns and bends. When designing hill roads the route is located along valley, hill sides and mountain pass. Most of the work has to be carried out in rock using explosives and retaining walls. Unfavorable geological conditions such as landslides may be encountered and special structures have to be provided to establish the stability of road. In locating the alignment of hill road and structures following points are considered.
Temperature: The temperature of air varies inversely with altitude. The temperature drop being about 0.5oC per 100 m of rise. Similarly the amount of heat received by hill slopes varies with their orientation in relation to the exposure to sun. On slopes facing south and south west snow disappears rapidly and rain water evaporates quickly.
Rainfall: The amount of rainfall in a hilly region is inversely proportional to the altitude. The maximum rainfall is in the zone of intensive cloud formation (1500-2500m) above the sea level after which it decreases substantially. Mountain range slopes with face winds coming in from the sea receive more rainfall than other side of the range.
Atmospheric pressure and winds: Atmospheric pressure is inversely proportional to altitude. At higher altitudes the velocities of wind increases. The change in character of wind is due to appreciable difference of atmospheric pressure on valleys and on mountain pass. The variation of atmospheric pressure and wind speed may cause snowfall, snow drift (mass of snow thrown by wind) and avalanches (mass of snow in mountains). So it is very important for designer to be familiar with the local climatic condition.
Geological condition: The degree of stability of hill slope depends upon the type of rock, the degree of strata inclination, hardness of rock and presence of ground rock. Sedimentary rocks have tendency to slip under the influence of force parallel to the layer. The instability of hill road may be due to ground water, landslide and unstable folds.

Route location: Hill routes tend to follow tortuous routes with large number of curves to bypass obstructions, to cross water courses and to develop the route for negotiating elevation differences. The approach to the location of hill road alignment varies for the section along the valley bottom (river route) and along the mountain pass (ridge route). There are both advantages and disadvantages of both locations.
River Route or Valley Route: The location of a route along the river valley is known as river route. River route is generally used in hill road due to comparatively gentle gradient. The advantages of river route are low vehicle operation cost, availability of water and other construction material in the vicinity. However, a river route may involve numerous horizontal curves, construction of large bridges over tributaries and on the stretches along steeply sloping hill sides, which in some places may be unstable. It may also be necessary to construct special structures and massive river training and protection structures on the valley sides to safeguard the road against washout, toe cutting etc.
Some of the consideration in locating the river route:
The road bed should be sufficiently above and away from the maximum water level in the river.
In narrow, constructed valleys with rocky slopes the bed frequently has to be placed near the water course. In such case the embankment slope facing the river should be adequately protected and stabilized.
When locating the route major attention must be given to the geological and hydrological structures of the valley slopes to provide stability.
To reduce the earth work, particularly along the excavation, the route should be located along the hill sides with lowest practical gradient.
When crossing water courses, several route alternatives may be investigated.
Ridge Route: A ridge route is characterized by very steep gradient, numerous sharp curves including hair pin bends and expensive rock work. The road usually follows the top section of the hill system and crosses successively mountain pass (location in the range of mountains that is lower than the surrounding peaks). The ridge route climb continuously up from the valley floor till it reaches a mountain pass and then descends down to catch another hill system. Geologically stable and comparatively mild slope sections are selected for the development of the route.  The route is traced in the map by following more or less the line of equal gradient.
(c) Gradient
The limiting gradients in mountainous and steep terrain over 3000 meters high above mean sea level are 5% and 6% respectively. At high altitudes above 3000 meters the power output of engine decreases so the gradient of road is decreased as the height increases.

5.2.2 Geometric Design of Hill Road
In the design of hill roads following factors are to be considered
Design Speed: As per NRS 2045, the design speed of the vehicle on different road and terrain  condition are given below: (Refer Geometric Design)

Types of Road Speed (kmph)
Level Rolling Mountainous Steep
Trunk Road 120 80 50 40
Feeder Road 100 60 40 30
District Road 60 40 30 25

Sight Distance:
 The stopping distance is given by; SSD = vt +v2/2gf
                                                                    v= design speed in m/s
                                                                    t = reaction time of driver
                                                                    f= coefficient of friction
Stopping sight distance consists of lag distance and braking distance.
If v is in kmph then,
SSD = 0.278Vt +V2/254f
The minimum stopping sight distance for various speeds is given in Nepal Road Standard. (Refer Geometric Design)

The overtaking sight distance is given by; OSD = vbt+vbT+2S+VT
                                                                                vb= speed of overtaken vehicle.
                                                                                t= reaction time (2 seconds)
                                                                                T = overtaking time
                                                                               S= minimum spacing between vehicles
                                                                                  = (0.7vb+6) m (empirical formula)
                                                                               V= speed of overtaking vehicle
Super elevation:
The super elevation to be provided at horizontal curves of hill road is calculated from the relation,
 e= v2/gR; v in m/s
 e= V2/127R; v in kmph
 For design V=0.75V then e = V2/225R
 Maximum super elevation = 7% and for hill roads 10%.
 Minimum super elevation = camber slope

Radius of Horizontal curve: The radius of horizontal curves in hill roads, is calculated by the formula;
Rminimum = V2/127(e+f)
Where, R = radius of curve
            V= design speed, kmph
             e=super elevation
            f= coefficient of friction

Widening of curves: Extra width of carriage way(we) at horizontal curves is calculated from the relation;
            we= +
where, n = number of lane.
             l= length of wheel base
             V= design speed, kmph
             R= radius of horizontal curve

Set back distance: As it is not practicable to provide visibility corresponding to overtaking sight distance all along the hill road, the alignment is made so as to provide at least the safe stopping sight distance.

Transition Curves: The length of transition curve is to be calculated from the formula;               L = v3/CR and C= 80/V+75 (0.5<C<0.8)                                                                                                                                              
Where, L= Length of Transition curve in meter
            R= radius in meter
            v= design speed in m/s
            V= design speed in kmph

Gradients: The limiting gradients in mountainous and steep terrain over 3000 meters high above mean sea level are 5% and 6% respectively. At high altitudes above 3000 meters the power output of engine decreases so the gradient of road is decreased as the height increases.

Hair pin bends: In aligning the hill road, it becomes necessary to attain height at a particular location without attaining substantial covering of horizontal distance. In such cases hair-pin bend is provided. When developing a route in hilly area, it is frequently necessary to insert sharp turning angle, within which it is very difficult and sometimes impossible to layout curves following normal geometric design.
Passing lane in hill roads
The construction of hill road is not only costly but also tedious work due to abrupt change in level, geological conditions and limited funds. Sometimes it is very difficult to cut the hard rock while sometimes it is very tedious to make stable flow ground. So the width of hill road is not uniform throughout. Width of hill road is fixed based on the geological conditions, traffic volume, and method of construction and availability of fund. At certain interval some extra space is provided to pass the traffic coming from opposite direction or to overtake the slow moving vehicle. This type of arrangement is known as passing lane in hill road.

Design and Types of Hair Pin Bends:
Design criteria for hair pin bends
The following design criteria should be adopted for planning hair pin bends (as per Indian Road Congress)
The straight length between two successive hair pin bends should be minimum of 60 m excluding the length of circular and transition curve.
Minimum design speed = 20 kmph
Minimum radius of inner curve = 14 m
Minimum length of transition curve =15 m
Superelevation in circular portion of the curve = 1 in 10
Minimum width of carriage way at the apex of curves should be 11.5 m and 9 m for two lanes and one lane respectively.
The maximum and minimum gradients should be 1 in 40 and 1 in 200 respectively at the curve.
For good visibility the island portion should be cleared of all the trees.



Fig: Hair pin bend
Figure Above shows symmetrical hair pin bend consisting of main curve ‘C’, reverse curves ‘Cr’ and tangents (straights) ‘m’. The acute angle of the bend is ‘α’. The main curve with the radius ‘R’ has a total length ‘C’ and subtends an angle ‘γ’ at the centre. Points A and B are located at the apex of the reverse curves. Between the ends of the reverse curves and the main curve of the bend, tangents must be introduced for the transitions of the super-elevation and extra width in the curve.
For the design and layout of hair pin bends elements such as radii of the main and reverse curves (R and r) and length of the tangent (m) are initially selected based on the site situations in conformity with the required geometric standards. The design of hair pin bends then basically consists of establishing the value of the turning angle ‘β’ at point A and B which satisfies the pre-selected parameters of the bend. For this purpose following simple expressions may be derived based on the geometry of hair pin bends as shown in figure.
Tangent length of reverse curve;
Where, T= length of the tangent
r = radius of reverse curve
β = deflection angle
The distance from the apex of the reverse curve angle to the commencement of the main curve is; AE = BF = T + m
From triangles, AOE or BOF it will be found that,


Where, R= radius of the main curve
From trigonometry, it is known that,

For equation (2) and (3)
 
Substituting this expression for tan(β) in preceding expression, solution for tan(β/2) becomes

Hence, the value of ‘β’ can be determined for corresponding value of m, R and r.

The central angle ‘γ’ corresponding to the main curve of the bend is equal to
γ =360 – 2(90 – β) – α = 180 + 2β – α
and length of the main curve is,

Hence the total length of bend is
S = 2 (Cr + m) + C ………………………………………. (7)
Where, Cr = length of the reverse curve
Having obtained these parameters, the hair pin bend can be plotted on the contour map or set out on the ground.
The expressions given above are for symmetrical hair pin bends having reverse curves with equal angles and of equal radii.
Hair pin bends are not desirable elements of hill road. In these bends speeds have to reduce substantially. The cost of construction also increases substantially because of the extensive volume of earthwork and retaining walls and also the vehicular operating cost. While designing hill roads, several route alternatives are investigated, preference being given to the one having least number of hair pin bends.

5.2.3 Different types of Hill Road Cross-Sections:
The cross-section of road in hilly region is determined by the original ground slope of the site, width of the roadway, shape and size of the drain etc. Following are the different cross-sections normally adopted in the construction of hill road.

Cut and Fill
Bench Type
Box Cutting
Embankment with Retaining Wall
Semi Bridge
Platforms

Cut and fill






Box Cutting:  In some cases, when the location of road bed is unstable or unsuitable along the hill side, the road bed is designed as trench type.
Embankment with retaining wall: In some cases, huge embankment has to be made, in such cases, a retaining structure should be provided in order to carry the earth pressure.

Fig: Box cutting and Stone-Masonry type of training structure with filling
Semi bridge: half portion of the road was made with the principle of bridge, but nearly half portion has natural ground surface

Figure 2, Semi-Bridge type of Cross-section

Semi tunnel


Figure 3, Semi- Tunnel

Platform

Figure 4, Reinforced Concrete Type, Platform







5.3 Special Structures in Hill Roads
The civil engineering structures provided in roads are retaining walls, revetment walls, cross drainage, toe wall etc. Special structures that are generally not provided in roads of plain terrain are referred as special/main structures in hill roads. On the basis of function of structures, these are classified into three groups:
Retaining structures
Drainage structures
Slope protection structures

Retaining structure: A retaining structure is usually a wall constructed for the purpose of retaining a vertical or nearly vertical earth bank which in turn support vertical load. It is most important structure in hill road construction. It provides adequate stability to the slope.
Design of retaining wall
The design of a retaining wall is done based on horizontal pressure by exerted by retained earth. Foundation as well as structural stability is considered carefully so that neither slip nor overturning occurs. As a thumb rule provided by Hager and Bonne the design of retaining wall is done in following way.
A section of 0.5H meter with a minimum width of 0.45 to 0.60 meter at top.
The rear side of retaining wall should be vertical while front batter of 1 in 4.
In the case of height greater than 6 meters, the base width of (0.4 H + 0.3) to         (0.5H + 0.6) m are adopted with a top width of 0.75 meters.
The rear face is kept vertical and filled with boulders and stones to improve drainage while front batter works out to 1:2.5 to 1:4.

Toe wall: - It is a low wall constructed at the bottom of an embankment to prevent slippage or spreading of the soil.

Figure 5, Retaining Structures at different Conditions, in Hill Road

Drainage structures: Drainage is one of the main problems during construction as well as in operation of roads. Some of the features of hill road drainage system are:
Drainage of water from hill slope: Surface water flowing from the hill slope towards the roadway is one of the main problems in drainage of hill road. In order to intercept and divert water from hill slope, catch water drains are provided, running parallel to the road way. Water intercepted by the catch drain is diverted by sloping drains and carried across the road by means of culvert. Energy dissipating structures like chute, rapids may have to be provided.
Road side surface drainage: Side drain is provided only on hill side of the road. Due to limitation in the formation width, the side drains are constructed to such shape that at emergency the vehicles could utilize this space for crossing at low speed or at parking. Normally, the shape of the side drains are angle, saucer and kerb and channel drains. In hard rock the lining is not necessary but in soft soil lining is necessary.
Sub-surface drainage: The seepage flow of water is one of the major problems during and after monsoons. Groundwater may seep across hill side above, below or at road level depending upon several factors such as depth of hard stratum, its inclination, quantity of ground water etc. Seepage flow causes problems on slope stability, weakens road and may cause pavement failure. This seepage flow can be controlled by suitable sub-surface drainage. (Refer chapter 6; Highway Drainage)
Cross-Drainage: As far as possible, cross drainage should be taken under the road and at right angle to it. At the head of small cross drains, catch pits are provided to collect debris, stone etc. to prevent scour. The floor level of catch pit is deeper than the inner level of the culvert by at least 30 cm.
------------------also refer drainage chapter -------------------

Figure 6, Angle, Shoulder and Kerb or Channel Drain
Slope Protection Structures: Fresh underfed embankment and cut slopes are the least stable part of road. Since the soil on the surface of the slopes is subjected to the direct action of sun, rain and wind with variation of moisture content in soil which becomes prone to failure. Flat slopes are provided for loose soil in embankment and cuttings. In stable soils, steeper slopes may be chosen. Steeper slopes may be chosen in the volcanic rock mass. In sedimentary rock, the permissible side slope depends mainly on the direction and angle of incidence of strata. If the strata are inclined towards road, the slopes of cutting should have gentle slopes and if strata is inclined away from the road or are horizontal the cut slopes may be near to vertical.
In case when steep embankment or cut slopes are to be provided then these slopes are to be protected against erosion of slip failure. Different measures of protection are Earthwork, Bioengineering, Water Management, slope work, anchor works, wall and resisting structures, Gully protection works, pile work etc.

----also refer drainage chapter----------------

 
6.0 HIGHWAY MATERIALS
6.1 Introduction and Classification of highway materials
Some of the materials like soil, stone aggregates, sand and bitumen which have some specific requirements, different than for general building purposes when used in road construction. In this chapter discussion is focused mainly on those materials, which are extensively used in road construction practices with special references as to their use, specifications, requirements, behavior in road construction and maintenance.
Most common materials used in road construction can be classified into three broad categories:
Mineral Materials: Mineral materials such as sub-grade soil, sand/stone dust (fine aggregates), stone chip, gravel/crushed aggregates (coarse aggregates), pit-run sand/river sand, blast furnace slag etc are used in road construction. These are either naturally occurring, semi-processed or fully processed. Soils are extensively for embankment construction and in the construction of soil stabilized layer. Stone aggregates are used in pavement construction and road side structures. These are also used as filter materials in the back fills behind retaining walls and in subsurface drainage.

Binding Materials: Binding materials include,
Stone dust or cohesive soil:  It results in semi-rigid and semi flexible bond between the mineral particles.
Cement, lime and other inorganic binding material: It forms rigid and irreversible bonds.
Bitumen, tar and other organic binding materials: It provides thin film of binding action which is flexible and reversible in nature.

Other Materials: Other common road construction materials such as reinforcement, timber, bricks, boulders, cobbles, gabion wires, geo-textiles, chemical additives,       Hume pipes, precast units etc.

When mineral materials are mixed with binding materials it produces several new forms of hard materials. These include water bound macadam, cement concrete, stabilized soil, cement soil, bitumen soil, lime concrete, cement mortar, bituminous bound macadam, bituminous carpet (asphalt concrete), grouted or penetration macadam etc.
6.2 Sub-Grade Soil  
Highway structure essentially consists of the components: the sub-grade for embankment upon which the pavement is laid and pavement itself. In cuts, sub-grade consists of parent soil. In filling section, the sub-grade/embankment consists of borrowed soil over the native ground or sometimes treated in case of poor soil.
Soil is formed by the disintegration or decomposition of rocks. Engineering properties of soil are largely dependent on the nature of parent rock. The properties and behavior of soil are greatly influenced by the changes in moisture content, density and degree of compaction. Soil contains air, water, organic matters and other chemicals all dispersed around the mineral particles.
6.2.2 Characteristics of sub grade soil
Detailed study of the characteristics of soil is the subject matter of soil science and soil mechanics. Certain characteristics of soil particles that is useful in predicting the performance and behavior of soils are:
Grain size and shape
Surface Texture
Chemical Composition
Moisture content
Dry density

Maximum dry density is obtained with minimum compaction effort at optimum moisture content. This is determined by standard or modified proctor density test. Soil is compacted to maximum dry density in order to use the following advantages of compacted soil.

Increase in strength
Rate of water movement through soil decreases with the decrease in voids.
Volume change due to variation in moisture content is less at maximum density.
6.2.3 Desirable Properties of soil as a Highway construction material
Soil as a highway construction material should have the following properties:

Stability
Incompressibility
Permanency in strength
Minimum changes in the volume under adverse condition of weather and ground water
Good Drainage
Ease in compaction
Road Aggregates
6.3.1 Definition, Classification of Road Aggregates
ASTM (American Society for Testing and Materials) has defined road aggregates as the inert materials, which when bound together into a common mass forms concrete, mastic, mortar, plaster etc.
Road aggregates as an aggregation of sand, gravel, crushed stone, slag and other material of mineral origin, used in combination with a binding medium to form bituminous mixes and cement concrete, macadam, mortar, mastic, plaster etc or alone as in filter beds and various sub-surface drainage system.
Road aggregates are mineral materials either naturally occurring (such as gravel, pit run or riverbed sand) of obtained by crushing rocks, boulders or stone.
Depending on the size of particles, stone aggregates are classified into coarse and fine aggregates. Coarse aggregate is an either uncrushed gravel or crushed stone processed in the crusher plant or combining of natural gravel and crushed stones, which retained in 4.75 mm IS sieve. Fine aggregate is an either natural sand or crushed stone which passes through 4.75 mm IS sieve.
Desirable Properties of Road Aggregates
Strength
Hardness
Toughness
Durability
Proper Shape
Good Adhesion
Cementation
Tests on Aggregates and their significance
As aggregates obtained from different sources differ considerably in their physical and engineering properties. It is necessary, therefore, to carry out various tests on aggregates to ensure not only that undesirable material are excluded from highway pavements but also that the best available aggregates are included.Aggregates tests may be divided into four main groups as given below:
AGGREGATE TESTS

Descriptive Tests
Particle Shape
Surface Texture
Non destructive Quality Tests
Gradation
Water Absorption
Shape
  FI, EI & AN

Durability Tests
Abrasion
-Aggregate Abrasion
-Accelerated Polishing
Strength and Toughness
-ACV
-10% Fineness
-AIV
-CBR
Soundness
-Frost susceptibility
-Na2So4 and MgSo4


Sp. Gravity Tests
Bulk Sp. Gravity
Apparent Sp. Gravity









Descriptive Tests
These tests are intended to define the visual examination of an aggregate that enables it to describe in terms of both the shape and the surface texture of the particles. This results in subjective descriptions of these mineral aggregate characteristics. The particle shape may be described as rounded, irregular, flaky, angular, elongated, flaky and both flaky and elongated.
Surface texture may be defined as glassy, smooth, granular, rough, crystalline, honeycombed and porous.

Significance of tests: The descriptive test is most useful in classifying aggregates. The descriptive classifications are in turn very valuable guides relative to the internal friction properties of aggregates. By internal friction is meant the properties, which resists the movements of aggregates pass each other. Road aggregates with high internal friction have good interlocking qualities.

Non-destructive Quality Tests
These non-destructive tests are carried out on the aggregate to determine its suitability for a specific use. The results obtained are normally compared with aggregate specifications to see whether they comply with the desired properties and characteristics. The tests of particular interest are the gradation, water absorption and shape test.

Gradation test: Gradation test is also known as Sieve Analysis, Screen Analysis and Mechanical Analysis. It represents the quantity expressed in percentages by weight of the various particle sizes of which the sample of aggregate is composed. This is determined by separating the aggregate into portions, which are suitably graded from coarse to fine. The results obtained may be expressed either as total percentage passing or retained on each sieve or as the percentages retained between successive sieves. The total percentage passing method is very convenient for the graphical representation of a grading and is most widely used in graded aggregate specifications.

Significance of tests:  Gradation is the characteristic of a road aggregate on which the greatest stress is placed in specifications, as it has direct influence on both the construction quality and the cost of pavement component.

Shape test: There are three mechanical measures of particle shape, which may be included in the specifications for aggregates for road construction. These measures are the Flakiness Index (F.I), Elongation Index (E.I) and Angularity Number (A.N.)

The Flakiness Index of an aggregate is the percentage by weight of particles, whose least thickness is less than three-fifths or 0.6 times of their mean dimension. The mean dimension is the average of two adjacent sieve apertures between which the particle being measured is retained by sieving. The F.I. test is not applicable to particles smaller than 6.35 mm in size. The desirable value of F.I. should be less than 15% and it should not exceed 25% in any case. Standard thickness gauge is used to gauge is used to gauge the thickness of sample.

The Elongation Index of an aggregate is the percentage by weight of particles whose greatest length is greater than 1.8 times their mean dimension. As with the F.I. test, the E.I. test is not applicable to aggregate size smaller than 6.35 mm.


Table 7.1 Dimension of Thickness and Length Gauges

The Angularity Number of an aggregate is the amount, to the nearest whole number, by which the percentage of voids exceeds 33 when an aggregate is compacted in a specified manner in a standardized metal cylinder. A.N. measures the voids in a sample after compaction in a particular manner.
The apparatus for testing the angularity number consist of a metal cylinder of 3 liter capacity and a tamping rod. Aggregate in specified range (16-20 mm) is placed and tamped 100 times by a tamping rod in three layers. Then it is weighed. Then it is emptied and filled with water.
Then A.N. =67-
Where, C- Weight of water to fill the cylinder
    G- Specific Gravity of aggregates
    W- Weight of aggregate in cylinder.
This value is expressed as the nearest whole number.

Significance of tests: The internal friction of an aggregate is the property, which by mean of the interlocking of particles and the surface friction between adjacent surfaces, resists particle movement under the action of an imposed load.

Water absorption test: This test is normally carried out in conjunction with specific gravity test. The procedure consist of soaking the aggregate sample in distilled water for 24 hours, surface drying and weighing in air and then oven drying and weighing in air again. Then the water absorption is given by,
WA = w1-w2/w2 *100
Where, WA = Water absorption
             w1 = weight of surface dried aggregate in air;
             w2 = weight of oven dried aggregate in air;

Significance of tests: Knowledge of the absorption properties of an aggregate is particularly important in bituminous surface design. The porosity of the aggregate affects the amount of binder required and additional binder material may have to be incorporated in the mixture to satisfy the absorption by the aggregate after the ingredients have been mixed. The water absorption values allowed for road aggregates normally range from less than 0.1 percent to about 2 percent for materials used in road surfacing, while values of up to 4 percent may be accepted in road bases.

Durability Test
Three types of resistance tests are carried out on road aggregate. These are the abrasion test, toughness tests and soundness test.

Abrasion Test: Different types of abrasion test have been developed in order to evaluate the hardness of aggregates under attrition. In the past Deval attrition test and the Dorry abrasion test were most widely used methods for abrasion test. In recent years, however, the Los Angeles abrasion test and accelerated polishing test are widely used.

The aggregate abrasion test is carried out in 5 or 10 kg (10 kg for coarse grading i.e. grading E,F,G and 5 kg for fine grading i.e. grading A,B,C and D) of aggregate depending in the gradation group. These aggregates are placed in a standard Los Angeles Abrasion Test Cylinder which is of 70 cm diameter and 50 cm length along with 4.7 cm diameter steel spheres. There is a steel projection of 8.8 cm x 2.5 cm x 50 cm inside the cylinder. The weight of abrasive charge varies from 390 gm to 445 gm. The cylinder drum is rotated at a speed of 30-33 revolution per minute for 500-1000 revolutions depending upon the gradation group. On completion of the specified revolutions the test sample is removed and sieved through 1.7 mm IS sieve. The materials passing through 1.7 mm sieve is weighed and the percentage loss in weight of the aggregate is calculated and this is called the abrasion value of the aggregate.

Original weight of the oven dry aggregate sample  = W1
Weight of the aggregate retained on 1.70 mm IS sieve after test = W2
L.A. Abrasion Value (LAA) = (W1 - W2)/ W1 x 100
Significance of tests: For an aggregate to perform satisfactory in a highway pavement, it must be sufficient hard to resist the abrasive effects of traffic over a long period of time. Numerous test results have shown, however, that aggregates with abrasive values greater than 30% are too soft for the wearing course of a bituminous surfacing. Aggregates having 30% or less abrasion value are good for high quality pavement surface layers while aggregates with 40% or less are acceptable for base layers. Sub-base materials may have up to 50% abrasion value.
 
Table 7.2 Standard Grading Group for LA Test

Strength and Toughness Tests: Toughness is defined as the power possessed by an aggregate to resist fracture under an applied load, then the tests in common usage which are reflective of this quality are the aggregate crushing test, ten percent fine test and the aggregate impact test.
Aggregate crushing value is a measure of the resistance of an aggregate to crushing under gradually applied compressive load. Aggregates used in road construction should be strong enough to resist crushing under traffic load. To achieve highly durable pavement aggregate possessing low aggregate crushing value should be preferred. The test is normally carried out on material passing the 12.5 mm and retained on the 10 mm IS sieve. The aggregate is placed in standard mould using a specified procedure and then a load of 40 tones is gradually applied at a uniform rate of 4 tones/minute to the prepared sample material for a period of ten minutes. The load is then released and the amount of material passing the 2.36 mm sieve is determined. This weight is expressed as a percentage of the total weight of the sample which is termed as the aggregate crushing value. The test is repeated for average value.
Total weight of the oven dry aggregate sample = W1
Weight of the crushed material passing 2.36 mm IS sieve after test = W2
Aggregate Crushing Value (ACV) = W2/ W1 X 100 %
Aggregate Impact Value gives a relative measure of the resistance of an aggregate of sudden shock or impact. The test is carried out by subjecting aggregate which has passed 12.5 mm and is retained on the 10 mm IS sieve, of 15 blows of  13.6 -14.1 kg hammer falling through a height of 381 mm. After 15 impacts the material passing the 2.36 mm sieve is expressed as a percentage of the total weight of original sample and termed as the aggregate impact value.
Total weight of the oven dry aggregate sample = W1
Weight of the crushed material passing 2.36 mm IS sieve after test = W2
Aggregate Impact Value (AIV) = W2/ W1 X 100 %
 
Figure 7.4 Aggregate Impact Test Apparatus
Significance of tests: In all form of flexible pavement, the aggregate must be tough enough to support the weight of the rollers during construction and the repeated impact and crushing actions of traffic. Thus the aggregate must have a durable resistance to both crushing and impact. The result obtained with the aggregate crushing test suggest that materials with values greater than about 35% are too weak to be utilized in a pavement. In the case of AIV, if AIV is less than 10% then aggregate is very strong, if AIV lies between 10%-20% then aggregate is considered to be strong and if AIV lies between 20%-30% then aggregate is said to be satisfactory.

California Bearing Ratio (CBR) Test is a measure of resistance of penetration of sample material to the standard rock under controlled conditions. The load is expressed as a percentage of standard load values to obtain specified deformation level and is defined as CBR value. It is a simple test and extensively investigated for field correlations of flexible pavement thickness requirements. The test consist of causing a cylindrical plunger of 50mm diameter to penetrate a pavement component material with standard load at the rate of 1.25 mm/minute for 2.5mm and 5mm penetrations.
CBR = Load on test sample at defined penetration level (2.5 or 5 mm)
Load on standard sample at same penetration level
Specimen from sample soil or base material is prepared at proctor maximum dry density at optimum moisture content. Sample in mould is soaked in water for four days (or unsoaked ) as the real ground condition dictates. Surcharge weight equal to the weight of layers above the layer of material under test on top of the test sample is placed the whole set on the penetration test machine. Set stress strain gauge to zero and apply load on plunger to result uniform penetration of 1.25 mm/min, record load reading penetration values of 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3 ,4, 5, 7.5, 10 and 12.5 mm. Plot the graph and obtain corrected value of load corresponding to the corrected penetration value and CBR value is obtained.
Soundness Tests: The stone used in pavement construction should be durable and should resist disintegration due to the action of weather. The property of the stones to withstand the adverse action of weather is called soundness. The aggregates are subjected to physical and chemical action of rain and ground water, the impurities there-in and that of atmosphere. Hence, it is desirable that the road stones used in the construction should be sound enough to withstand the weathering action.
Clean, dry aggregate specimen of specified size range is weighed and counted. It is immersed in the saturated solution of sodium sulphate or magnesium sulphate for 16 to 18 hours. Then the specimen is dried in oven at 105-110oC to a constant weight, thus making one cycle of immersion and drying. The average loss in weight of aggregates to be used in pavement construction after 10 cycles should not exceed 12 percent when tested with sodium sulphate and 18 percent when tested with magnesium sulphate.

Specific Gravity Test
This test is carried out in the laboratory by soaking a sample of the aggregate in distilled water for 24 hours, weighing it in water at the end of this period, surface drying and weighing in air and then weighing in air again after oven drying for 24 hours. The test is usually carried out in conjunction with the water absorption test.
Gb = W
W1-W2
Bulk Specific Gravity is given by,


Where, W = Weight of oven dry sample in air
             W2 = Weight of saturated sample in air
             W1 = Weight of saturated sample in water.
Significance of tests: As road aggregates are usually proportioned by weight, a specific gravity value is of vital importance in determination of the proper mixture. Gradation specifications are valid only if the coarse and fine fractions have approximately the same specific gravity.
Comparing Gradation Specification and Method of Translating Specification




















6.3.5 Combination of Aggregates:
A good asphalt concrete pavement requires more than asphalt, aggregates and equipment. Asphalt concrete requires the combination of two or more aggregates, having different gradations, to produce an aggregate blend that meets gradation specifications for a particular asphalt mix.
Method-1, Trial and Error Method:
Mathematical procedures are available to determine an optimum combination of aggregates, but the “Trial and Error Method” guided by a certain amount of reasoning is the most practical procedure to determine a satisfactory combination.
Step-1, Obtain the required data:
The gradation of each aggregate must be determined
Select the specification range
Step-2, Select a target value for trial blend,
The target value for the combination must the within the design limits of the specifications.
Step-3, Estimate the Proportions,
Estimate the correct percentage of each aggregate needed to get a combined gradation near the target value. For example 30-70%, 40-60% etc.
Step-4, Calculate the Combined Gradation,
This calculation will show the result of the estimate from step-3.
Step-5, Compare the result with the target value,
If the calculated gradation is close to the target value, no further adjustments  need to be made, if not, an adjustment in the proportions must be made and the calculations repeated until the result is closer to target.
Sieve Size Aggregate-1 Aggregate-2 Target Range
20 mm 100 100 100
12.5 mm 100 94 95-100
10 mm 94 65 90 max
No. 8 52 27 34-50
No. 200 7.1 1.2 2-10
 Example-1, Determine the amount of aggregate-1 and aggregate-2 to be blended in order to get the target specifications: Given in the table attached herewith the data regarding percentage passing of two aggregate samples and the required combined aggregate.
Solution:
Step-1, Obtain the required data:
Given in question
Step-2, Select a target value for trial blend,
Sieve Size Aggregate-1 Aggregate-2 Target Value Target Range
20 mm 100 100 100 100
12.5 mm 100 94 97.5 95-100
10 mm 94 65 <90 90 max
No. 8 52 27 42 34-50
No. 200 7.1 1.2 6 2-10
.







Step-3, Estimate the Proportions,
The first estimate might be 50% of aggregate-1 and 50% of aggregate-2.

Sieve Size Aggregate-1 Aggregate-2 Total Blend Target Value Target Range
20 mm 100 100 100 100 100
12.5 mm 100 94 97 97.5 95-100
10 mm 94 65 80 <90 90 max
No. 8 52 27 40 42 34-50
No. 200 7.1 1.2 4.2 6 2-10

Step-4, Calculate the Combined Gradation,
This calculation will show the result of the estimate from step-3.


Step-5, Compare the result with the target value,




Method-2, Graphical Method:
Procedure:

















Method-III Analytical Method:




















Unsolved Problems:
B. S. Sieve size, mm % Passing of aggregate on given sieve size Specifications
Agg - A Agg - B Agg - C Limits Mid Point
25.0 100 100 100 100 100
12.7 100 100 94 90-100 95
4.76 100 100 54 60-75 67.5
1.18 100 66.4 31.3 40-55 47.5
0.300 100 26.4 22.8 20-35 27.5
0.15 73.6 17.6 9.00 12-22 17.00
0.075 40.1 5.00 3.10 5-10 7.5
B. S. Sieve Size  (mm) % of material
Passing Retained
25.4 0
25.4 12.7 25-45
12.7 4.76 10-25
4.76 2.36 6-10
2.36 1.18 6-9
1.18 0.425 8-13
0.425 0.180 7-13
0.180 0.075 7-12
0.075 2-8
Q1. The size of fine, intermediate and coarse aggregate from the crushing plant and desired specifications of aggregate for road construction is given in table below. Determine by the mathematical method, the proportion of aggregate A, B and C to be mixed to produce an aggregate complying with the given specification.

Q2. Translate the specification of aggregate given table in terms of individual percentage of material retained on each size to percentage of material passing in sieve
















6.4 BITUMINOUS ROAD BINDERS
6.4.1 Definition and Classification of Road Binders
When the term bituminous road binder is used, it usually refers to two types of binders i.e. bitumen binder and tar binder. Though the tar is different than bitumen in all aspect, the tar is discussed here as it is also used as a binding material and that it falls in the group of organic binding material.
Bituminous Road Binders







Road Bitumen Road Tar






Natural Bitumen Petroleum Bitumen





Lake Asphalt (Trinidad Lake Asphalt 54% bitumen) Rock Asphalt (France/Switzerland)  4 -18 % bitumen Penetration Grade Bitumen Liquid Bitumen




Cutback Bitumen Emulsion
Figure 7.5 Classifications of Bituminous Road Binders

Bitumen
Bitumen is a viscous liquid or solid material black or dark brown in color, having adhesive properties, consisting essentially of hydrocarbon, derived from crude oil fractional distillation or from asphalt occurring in natural form and soluble in carbon disulphide. Because of their water proofing and binding character, they are used in road construction.
When bitumen contains some inert material or minerals it is called asphalt.

Natural Bitumen
The largest natural deposit of bitumen in the world occurs on the island of Trinidad off the north coast of South America and is called Trinidad lake asphalt. The largest deposit of rock asphalt is found in Switzerland and France. The Swiss deposit is believed to have been formed by the decomposition marine animals and vegetable matter. On the other hand the French deposit was formed probably as a result of penetrating oil into the rock mass.




Petroleum Bitumen
These are the bitumen obtained in crude oil refinery plants and are also called refinery bitumen. Some times they are also called as residual bitumen, straight run bitumen or steam refined bitumen.
Various volatile constituents are separated by the process called fractional distillations, which consist of heating the crude oil at successively higher temperature and separating the materials at specified temperature. The product obtained in crude refinery process is petrol, and then kerosene, diesel, lubricating oil and the residue is petroleum bitumen. When the residue is further processed to a definite consistency without additional treatment the product is known as straight run bitumen.
Straight run bitumen is classified into 9 different grades. This classification is based on the penetration value of the bitumen which is determined by standard penetration test. According to this classification they are 15 pen, 25 pen, 35 pen, 50 pen, 70 pen, 100 pen, 200 pen, 300 pen and 450 pen bitumen. In India it is classified as 15/30, 30/50, 70/80, 80/100,100/120. Normally in Nepal 80/100 bitumen is specified for the construction.

The process of manufacture of bitumen is accomplished in oil refinery plant in several stages as:
Pumping of crude oil
Dehydration of crude oil
Fractional Distillation
Steam Distillation in Reduced pressure
Straight Run Bitumen/Penetration Grade bitumen

6.4.2 Liquid Bitumen: Cutback bitumen and Bitumen Emulsion
Penetration grade bitumen normally ranges from being viscous to semi-solid in consistency at normal temperature, for the workability it is normal to heat the bitumen before use in road construction. When it is undesirable and not necessary to use hard bitumen, preference is given to use of liquid binders such as cutback and emulsion
Cutback Bitumen: Cutback bitumen is the bitumen, the viscosity of which has been reduced by using volatile solvent and can be applied directly in road construction. The usual practice is to use petrol, kerosene oil or diesel.
The purpose of cutback is to increase fluidity. Increasing fluidity has the following advantages.
Substitute of heating (helps to protect environment)
Suitable for direct application
Good mixing for manual method
Mix can be transported for long distance without setting
Can be used as dust palliatives

Types of Cutback: Cutback may be of three different categories. If the bitumen is mixed with low volatile (diesel) it is known as Slow Curing (SC) cutback bitumen. If the fluidity is increased by adding medium volatile agent such as kerosene, the cutback bitumen is known as Medium Curing (MC). Mixing of bitumen with highly volatile solvent such as petrol or naphtha is used to prepare the Rapid Curing (RC) cutback bitumen. If the traffic should be let shortly after laying, RC cutbacks should be used and if aggregates are not very clean and are dusty SC cutback would be proper choice.

Each category of cutbacks can be divided into six different grades in the viscosity determined by standard tar viscometer. This is an old grading system. The new system is based in kinematic viscosity of the mixture and has five different grades.

                  OLD                                                                            New
   SC - 0, 1, 2,3,4,5                                                                  SC – 70, 250,800,3000
   MC- 0, 1, 2,3,4,5                                                                 MC- 30,70,250,800,3000
   RC- 0, 1, 2,3,4,5                                                                  RC - 70, 250,800,3000

Uses: The following uses of cutbacks are recommended:

SC: in fine cold asphalt and as dust palliative materials.
MC: it has good aggregate coating (most useful when fine graded and dusty material are incorporated in a road surface) and also in bituminous soil stabilization.
RC: useful when a quick change back to the residual semisolid binding agent is desired.

Bitumen Emulsion:
An emulsion is relatively stable suspension of one liquid on a stage of minute subdivision, dispersed throughout another liquid in which it is not soluble. When the bitumen is suspended in finely divided condition in an aqueous medium and stabilized with emulsifier, the material is called emulsion. In bitumen emulsion, bitumen is the dispersed liquid.
All grades of bitumen and cutback can be emulsified but 100 and 350 pen grade bitumen are most commonly used in road construction practices. Emulsifier used widely in the preparation of bitumen emulsion belongs to two main categories. Anionic emulsifier(sodium stearate) and cationic emulsifier (amine salts).

Depending upon the type of emulsifier used in stabilizing emulsion, bitumen emulsion can be anionic emulsion and cationic emulsion. Anionic bitumen emulsion are further classified into labile, semi stable and fully stable.

Road Tar
Road Tar is a viscous liquid black in color, with adhesive properties obtained by the fractional distillation of crude tar. Crude tar is produced by destructive distillation of coal, wood, shale etc. By destructive distillation is meant the subject of the raw material is heated alone without access to air.

Types of Road Tar: Indian Standard classifies road tar in five different grades: RT-1, RT-2, RT-3, RT-4 and RT-5 based in part by their viscosity. RT-1 grade have very low viscosity and RT-5 has highest. Typical use of RT-1 grade tar is for surface painting in very cold climates, RT-2 for normal climatic condition and RT-5 is commonly used for grouting.

Comparison between Bitumen and Tar:
Both bitumen and tar binders can be used in road construction in varied conditions. The right choice in case of option can be made if differences between these binders are known. Each of these binders has particular advantages in certain situations. Bitumen and tar differ in chemical composition too.

Tar

It has black to dark brown color.
It is the fractional distillation of crude tar obtained by destructive distillation of coal.
Different chemical constituents than that of bitumen.
It coats aggregate more easily and retains it better even in presence of water.
It is more temperature susceptible.
It has inferior weathering resistance.
It contents more free carbon.
It is recommended to use in service stations, fuel station area as tar does not loss viscosity in oil.
It is soluble in Toulene. Bitumen

It has black to dark brown color.
It is the product of fractional distillation of crude oil.
Different chemical constituents than that of Tar.
It coats aggregates difficultly as compared to tar.
It is less temperature susceptible.
It has superior weathering resistance.
It contents less free carbon.
It is not recommended to use in service station, fuel station area due to solubility in petroleum oil.
It is soluble in Carbon disulphide CS2 and Carbon Tetrachloride CCl4

6.4.3 Tests on Bituminous Binder and their significance
In order to aid the engineers in ensuring that the material obtained from the suppliers has the desired qualities, a number of tests have been devise which attempt to measure various binder properties for particular reasons. The various tests on bitumen may be divided into following four categories.

Consistency Test:  Consistency test indicates the property of binder to flow. It is the function of temperature.
Composition Test: As the quality of binder depends upon its compositions a number of test have been developed to determine the properties of specific fractions and components of the bituminous binder.
Specific Gravity Test: It is used in establishing the relation between binder weight and volume for transporting and billing purpose, in the design of bitumen mixes and so on. Comparing specific gravity of the supplied bitumen with the specific gravity of standard bitumen also gives rough idea in its purity.
Safety Test: Flash and fire point test is the most common test in this category.


Consistency Test
Penetration Test:  Penetration test determines whether the bitumen under specified temperature is hard or soft. Value obtained by penetration test is the measure if hardness or softness of bitumen. It is a measure of consistency of semi solid bitumen.
This test consists of determining how far a standard steel needle will penetrate vertically into binder under standard conditions of temperature, load and time. The penetrometer consists of a needle assembly with a total of 100 gm and device for releasing and locking in any position. There is a graduated dial to read penetration values to 1/10th of a millimeter.


 Figure 7.6 Penetration Test Concept                                          
Figure 7.7 Penetrometer


Bitumen is heated to the pouring consistency, stirred thoroughly and poured into testing container to a depth at least 15 mm in excess of the expected penetration. The sample container is placed in a temperature controlled water bath at a temperature of 25oC for one hour. The sample container is taken out and the needle is arranged to make contact with the surface of the sample. The dial is set to zero or the initial reading is taken and the needle is released for 5 seconds. The final reading is taken on dial gauge. Three penetration tests are made on this sample by testing at distances of at least 10 mm apart.

Significance of tests: The penetration test is carried out to classify bitumen into different grades. In BS (UK) literature the ranges starts from 15 (Hardest bitumen) to 450 units (softest bitumen). In India bitumen are available with penetration values varying from 20 to 450. Bitumen with low penetration values are known for bad cracking. Lower penetration values are recommended for use in hot climates and higher penetration values in cold climates. Cohesive bonds with lower penetration bitumen are stronger than with higher penetration bitumen.

Ductility Test: A ductile material is one which elongates when it is in tension. The ductility of bituminous binders is expressed as the distance in centimeters that a standard semi solid briquette will elongate before breaking.
The binders which do not possess sufficient ductility would crack under repeated traffic loads. The test measures the adhesiveness and elasticity of bitumen. The test is carried out in a standard ductility test apparatus. Specified conditions for ductility test are:
Mould                                         -      8 shaped standard dimension
Temperature                                -      27oC
Pull rate                                       -       50 mm/min
Starting minimum width (neck)  - 10 mm x 10 mm

The ductility apparatus functions as a constant temperature water bath and a pulling device. Two clips are pulled apart horizontally at a uniform specified speed. The bitumen is heated to the pouring consistency, stirred thoroughly and poured in the mould assembly and placed on plain glass plate. The plate assembly along with the sample is cooled in air and then in water bath maintained at 27oC. The mould assembly containing sample is placed in water bath for 85 to 95 minutes. The distance up to the point of breaking of thread is reported in centimeter as ductility value.

 
Figure 7.8 Apparatus for ductility test
  Figure 7.9 Ductility Test Concept and mould
Significance of tests: The ductility value is the measure of adhesives and elasticity of bitumen. Its range varies from 5-100 cm and the most appropriate value is 50 cm.. Ductile bitumen forms thin ductile films around aggregates and do not crack under lower temperature. Bitumen possessing high ductility is also usually highly susceptible to temperature change, while low ones are not.
3. Viscosity Test: The viscosity of bitumen in road construction practice is based on the arbitrary test results obtained with orifice type viscometer. This test is carried out to determine the viscosity of bitumen which remains fluid under specified temperature of test. Specified conditions for test are as follows:
Apparatus                                    -                         orifice type viscometer
Diameter of orifice                     -                          4 and 10 mm
Temperature                               -                          25oC and 40oC
Quantity of bitumen                   -                          50 cc
The orifice type viscometer is used to determine viscosity of liquid bitumen like cutback bitumen and emulsion. The standard orifice viscometer test measure the time in second for a 50 ml of binder liquid flow from a cup through a standard under the above specified test conditions. Higher the viscosity of the binder higher will be the time required.

Figure 7.10Viscosity test concept
Significance of tests: The viscosity of bituminous binder is its most important physical characteristics. It is defined as inverse of fluidity and is measure of resistance to flow. The right choice of bitumen can be made after knowing its viscosity because of following reasons:-
The degree of fluidity of the binder at the application temperature determines the quality of mixing.
Binder of higher viscosity requires more compactive effort.
Premixes with higher viscosity binder are not easily workable.
There is no problem of getting the pumping pipes blocked if viscosity is low.
Binder with low viscosity is required for surface dressing, but too low viscosity will also result in bleeding or loss of chipping under traffic.
The viscosity of the bitumen and tar binder carries in a very wide range of 10-140 seconds. The viscosity values should therefore be mentioned with the test temperature and orifice size in every case.
Equi-viscous temperature (evt) is defined as the temperature at which viscosity is 50 seconds.

4. Float Test: Float test is the means of determining consistency of bitumen of those ranges of bituminous binder for which both penetration and viscosity tests cannot be applied. In this test, viscosity is measured in terms of time taken for water in seconds to force its way through the bitumen plug put in a mould of float test apparatus. The temperature of test is 50oC and the result is known as the float value.

Softening Point Test:  Softening point is the temperature at which the bitumen attains a particular degree of softening under specified conditions of tests. Softening point of the bitumen sample is carried out in Ring and Ball test apparatus. The apparatus essentially consist of a brass ring and steel ball. The ring is plugged with sample of bitumen, which is heated at a rate of 5oC per minute till the bitumen softens and touches the bottom of the metal plate placed at a specified distance (2.5 cm) below the ring. This temperature is the softening point of the bitumen.
Significance of tests: The softening point of bitumen used in pavements construction varies between 35oC – 70oC. It indicates how susceptible the bitumen with respect to the variation in temperature. Bitumen of same penetration values with higher softening point is less susceptible to temperature than for same grade bitumen having less softening point.

                                                              Figure 7.11Softening point Test setup
B. Composition Test
1. Distillation Test: This test is used to determine the quantity and quality of volatile constituents and amount of non-volatile residues present in cutback bitumen and binder emulsion. In emulsion the volatile constituents are primarily water. A specified amount of binder under this test is heated up to 360oC in a standard flask attached to a glass water cooled reflux condenser and a graduated receiver. Specified rate of heating is applied and then determine the amount of distillate removed from the binder.
Significance of tests: The result of distillation test can be to identify the type of volatiles in the binder and on the rate at which these volatiles will be lost under field conditions, enable to close check to be done on the quality of the binders on the road projects.
2. Water Content Test: The test is used to determine the amount of water present in a given sample of bitumen. Water content may be determined from distillation test too. When only water content is to be determined then this individual test is carried out by mixing pure petrol with the sample heating and distilling. The condensed water is expressed in percentage of total weight of original sample.
Significance of tests: Water content in bitumen should be less than 0.2% if bitumen is to be heated above 100oC. Higher water content results in foaming when heated.
Loss on heating test:  In this test a 50 gm of bitumen sample is placed in a small container and left for 5 hours, in a revolving aluminum shelf oven, the temperature of which is maintained at 165oC. At the end of heating period, the sample is cooled to room temperature and weighed. Loss in weight of the sample is then expressed as a percentage of the original weight.
Significance of tests: This test is carried out to compare the maximum loss of weight with the specified ones.
Ash content Test: The content of bitumen is the percentage by weight of the inorganic residue left after ignition of the bitumen sample. A specified amount of bitumen sample is gently heated until it begins to burn and then it is fired till the ash is free from carbon. The ash content is expressed in percentage of the total weight of the original sample.
Significance of tests: This test is carried out on both penetration grade or cutback bitumen. Test is used to ensure that undesirable amounts of mineral matter are not present.
Solubility Test: In determining the percentage of solubility of bitumen different solvent can be used. For the bitumen normally Carbon disulphide is used. A specified quantity of bitumen is dissolved in a given quantity of solvent. After filtering the solution through a fine-porosity filter paper, the residue retained is determined and the percentage of soluble material is calculated.
 Significance of tests: This test determines the amount of impurities in the bitumen. The solubility requirement of bitumen is 99.5% in CS2.
C. Specific Gravity Test
The specific gravity of bitumen is the ratio of the weight of a given volume of material at a given temperature to that of an equal volume of water at same temperature. There are two methods as given below:
Pycnometer method:
Specific gravity    =      (w3-w1) / (w2-w1)-(w4-w3)
Where,
  w1 = weight of the specific gravity bottle
w2 = weight of the specific gravity bottle filled with distilled water
w3 = weight of the specific gravity bottle about half filled with bitumen
      w4 = weight of the specific gravity bottle, about half filled with bitumen and rest with distilled water.
Balance  method:
Specific gravity =   w1/ (w1-w2)
Where, w1 = weight of the dry specimen
      w2= weight of the specimen immersed in distilled water
Significance of tests: Specific gravity values are to be determined for establishing relation between weight and volume of binder needed for the transportation and billing purpose. Specifications of binders in road surfacing are normally expressed as percentages by weight whereas they are usually shipped and measured by volume.

D. Safety Test
The flash and fire point test are the two tests under safety test. The flash point is the lowest temperature at which the vapor of the bitumen binder momentarily takes fire in the form of a flash under specified conditions test. The fire point is the lowest temperature at which the bitumen binder gets ignited and burns under specified conditions of test.
The flash point test is determined by heating a sample of binder at a uniform rate, while periodically passing a small flame across the surface of the material. The temperature at which the vapor given off by the binder first burn with brief flash of blue flame is called the flash point. If the heating is continued until the vapor continues to burn for a period at least by 5 seconds, the temperature at which this occurs is called fire point.
Significance of tests:  Bitumen binders leave out volatile material when heated at high temperatures depending upon their grade. These volatile agents may catch fire causing flash. This flash point indicates the maximum temperature to which the binder can be safely heated. The flash point indicates the temperature to which the binder can be safely heated. The flash point of most penetration grade bitumen lies in the range of 245 to 335oC. The minimum specified flash point of bitumen used in pavement construction is 175oC.
6.5 Bituminous Mixes:
6.5.1 Definition and Classification
Asphalt Concrete Mixed Design
Asphalt concrete is the highest type of premix in the group of black top pavement. Normally, it is required to lay on the road having heavy traffic volume for the long road life and better serviceable condition.
Asphalt concrete is the dense graded premixed bituminous mixture consisting of carefully proportioned mixture of dry coarse aggregate, fine aggregate, mineral filler and bitumen.
Design of Asphalt Concrete
For the design of asphalt concrete, it is preferable to study first the types and causes of failures in bituminous surfacing. The basic concept is to attempt for minimizing failures in the pavement made of bituminous mixes. Bituminous surfacing may fail due to instability, disintegration or fracture. Early loss of skidding resistance may occur in soft stone aggregates. The following points should be considered regarding design requirements for the material used in premix based on the types and cause of failure in bituminous surfacing.
Select a good quality, relatively hard and hydrophobic, rough textured aggregate of a grading which will meet the requirement of workability, permeability, economy and with high polishing value for the wearing course.
For the aggregate selected, choose a binder whose consistency is sufficiently soft to ensure good workability and long life, but is still hard enough to provide adequate tensile strength and resistance to moisture.
Use as much binder as possible but not in excess that causes losses of stability.

Design Procedure
The design of asphalt concrete mixes primarily consists of three basic steps which include:
Selection of aggregates
Selection of binder and
Determination of optimum binder content

The first two steps are intended to formulate the specification of materials proposed for dense bituminous mixes while third one is meant to establish optimum binder content to ensure maximum stability. The specification of material is formulated on the basis of availability of material, method of construction and desired work specification to achieve for the end product. Many empirical and semi-empirical design procedures are in use but Marshall Test and design method is the test which has the greatest international acceptance.

There are two main approaches to determine the optimum binder content. These are surface area concept method and void concept method.
Surface Area Concept Method is based on the requirements that the binder must be enough to form thin film around all mineral particles but not more in such a way as to allow binders to take more space in the voids available in mineral mass. It must be remembered that bitumen is not meant for strength. Stability of bituminous mixes is obtained basically as a result of mineral materials interlocking and not from the binders, although binders film will ensure required cohesion to make particles together.
The Void Concept is based on promise that the void in the mineral mass must be minimized to ensure stability not by the binder but by the selection of appropriate well graded material wherein the quantity of bitumen must be enough to ensure that all mineral particles would be coated with thin film of binders without forming thick coat. Thus, in the voids concept, voids are minimized in a way as to minimize space for binders by careful selection of mineral aggregates and those minimum voids are filled with binders.

6.5.2 Marshal Method of Bituminous Mix Design:
Objective
(i) To determine the optimum binder content
(ii) To check whether the hot-mixed asphalt concrete possesses the required strength
(iii) The combinations of aggregates to get optimum density

Apparatus Required:
The following apparatus are required to conduct the test
Breaking Head : The breaking head consists of upper and lower cylindrical segments or test heads having and inside radius of curvature of 50.8 mm accurately machined. The lower segment shall be mounted on a base having two perpendicular guide rods or posts extending upward. Guide sleeves in the upper segment shall be in such a position as to direct the two segment together without appreciable binding or lose motion on the guide rods.
Loading Jack: The loading jack shall consist of a screw jack mounted in a testing frame and shall produce a uniform vertical movement of 50.8 mm/min. An electric motor may be attached to the jacking mechanism.
Ring Dynamometer Assembly or Electric Equivalent or Probing Ring: One ring dynamometer of 2267 kg capacity and sensitivity of 4.536 kg and 11.34 kg between 453.6 and 2267 kg shall be equipped with a micrometer dial. The micrometer dial shall be graduated in 0.0025 mm. upper and lower ring dynamometer attachments are required for fastening the ring dynamometer to the testing frame and transmitting the load to the breaking head.
Flowmeter or Dial Gauge:
Water Bath: The water bath shall  be at least 152 mm deep and shall be thermstaticlly controlled so as to maintain the bah at tempreture 60± 10C. The tank shall have perforated false bottom or be equipped woth a shelf for supporting specimen 51 mm above the bottom of the bath.
Air Bath: The air bath for asphalt cutback mixtures shall be thermostatically controlled as shall maintain the air tempreture at 25± 10C
Thermometer:

Theory:
Bruce Marshall, formerly Bituminous Engineer with Mississippi State Highway Department formulated Marshall Method for designing bituminous mixes. Marshall’s test procedure was later modified and improved upon by U.S. Corps of Engineer through their extensive research and correlation studies. ASTM and other agencies have standardized the test procedure. Generally, this stability test is applicable to hot-mix design of bitumen and aggregates with maximum size 2.5cm. In Nepal also bituminous mix is commonly designated by Marshall Method, based on IRC.
In this method, resistance to plastic deformation of a cylindrical specimen of bituminous mixture is measured when the same is loaded at the periphery at a rate of 50.8 mm per minute. The test has two main features
Density – voids analysis
Stability – flow analysis
The stability of the mix is defined as a maximum load carried by a compacted specimen at a standard test tempreture of 600C. The flow is measured as the deformation in units of 0.25 mm between no load and maximum load carried by the specimen during stability test.

Procedure
Collection of Materials and Instrument setup
Specimen Preparation:
Preparation of aggregates
Selection of Aggregates:
Aggregates which possess sufficient strength, hardness, toughness and soundness are chosen keeping in view of availability and economic considerations.

















Selection of Aggregate Grading:

Sieve Size, mm Percent Passing by weight
Grade-1 Grade-2
20 - 100
12.5 100 80-100
10 80-100 70-90
4.75 55-75 50-70
2.36 35-50 35-50
0.6 18-29 18-29
0.3 13-23 13-23
0.15 8-16 8-16
0.075 4-10 4-10
Binder content by % wt of mix 5-7.5 5-7.5
 The aggregate that we are using for the preparation of sample should be of specific grading. IRC recommendation for 40 mm thick bituminous concrete surface course is given in table:
Determination of Specific Gravity:
Specific gravity of each aggregate to be combined to make the above grade has to be determined by using the formula:
G=(Wt in Air)/(Wt in Air- Wt in Water)
Proportioning of Aggregates:
The proportioning shall be done either by analytical method or by graphical method.
The aggregate combination thus obtained is taken approximately 1200 gm and is heated to a temperature of 1750C to 1900C.

Preparation of bitumen
Bitumen is heated to a temperature of 121 to 1250C with the first trial percentage of bitumen (say 3.5 or 4% by weight of the material aggregates) to the heated aggregates.

Preparation of Specimen and place in mould
The aggregates and the bitumen is thoroughly mixed at tempreture of 1540C to 1600C and the mix is placed in a preheated mould (about mixing tempreture of 138 to 1400C)
The mix in the mould is compacted by a rammer (of weight 4.54 kg with the fall of height 45.7 cm) with 50 number of blows (in some standard 70 blows are also taken, in such cases, the recommended Marshall stability value  will be higher) on either side at a tempreture of 138 to 1490C.
The weight of mixed aggregates taken for the preparation of the specimen maybe suitably altered to obtain a compacted thickness near with 63.5 mm. Three of four specimens may be prepared using each trial % of bitumen content.

Sample extraction
The compacted specimens are cooled to room tempreture in the moulds and then removed from the moulds using a specimen extractor. The diameter and mean height of specimen are measured and they are weight in air and in water.

Test temperature
The specimens are kept in thermostatically controlled water bath at 60± 10C for 30 to 40 minutes. The specimens are taken out one by one, placed in Marshall Test head and tested to determine Marshall Stability and flow.

Determination of the properties of the mix
Theoretical specific gravity of mix, Gt
Theoretical specific gravity Gt is the specific gravity without considering air voids, and is given by:
  …………………………………………………………… (1)
Where, W1 is the weight of coarse aggregated in the total mix, W2 is the weight of fie aggregate in the total mix W3 is the weight of filler in the total mix, Wb is the weight of bitumen in the total mix. Similarly G1, G2, G3 and  Gb are the apparent specific gravity of the respective materials.
Bulk specific gravity of mix; Gm
The bulk specific gravity or the actual specific gravity of the mix is the specific gravity considering air voids and found by:
  …………………………………. (2)
Where Wm is the weight in air and Ww is the weight of mix in water.
Air void percent or Volume of Voids; Vv
The volume of voids is the percent of air voids by volume in the specimen and is given by  ………………………………………………. (3)
Where Gt is the theoretical or apparent specific gravity of the mix as given in equation-1 and Gm is the bulk or actual specific gravity as given by equitation-2
Percent volume of bitumen; Vb
The volume of bitumen is the percent of volume of bitumen to the total volume and is given by:
   ………………………………………….. (4)
Voids in mineral aggregates; VMA
Voids in mineral aggregates, VMA, is the volume of voids in the aggregates, and is the sum of air voids and volume of bitumen, and is calculated from :
VMA = Vv + Vb ………………………………………………………………. (5)
Voids filled with bitumen; VFB
Voids filled with bitumen, VFB, is the voids in the mineral aggregate frame work filled with the bitumen, and is calculated as:
  …………………………………………………….... (6)

Determine marshall stability and flow
Marshall stability of test specimen is the maximum load required to produce failure when the specimen is preheated to a prescribed temperature (600C) placed in a special test head (of radius 50.8 mm) and the load is applied at a constant strain (50.8 mm per minute). While the stability test is in progress dial gauge is used to measure the vertical deformation of the specimen. The deformation at the failure point expressed in units of 0.25 mm is called the Marshall Flow value of the specimen.
Volume of specimen in cc Thickness of specimen in mm Correction factor
457-470 57.1 1.19
471-482 58.7 1.14
483-495 60.3 1.09
496-508 61.9 1.04
509-522 63.5 1.00
523-535 65.1 0.96
536-573 66.7 0.93
547-559 68.3 0.89
560-573 69.9 0.86

Apply stability correction
 It is possible while making the specimen the thickness slightly vary from the standard specification of 63.5 mm. In correction table the correction factor is given for every change in 1.6 mm thickness of the specimen with corresponding volume. Therefore, measured stability values need to be corrected to those which would have been obtained if the specimens had been exactly 63.5 mm. This is done by multiplying each measured stability value by an appropriate correlation factors as given in table:
Corrected thickness = Measured thickness*Correction Factor

Prepare graphical plots
The average values of the above properties are determined for each mix with different content and the following graphical plot are prepared:
Binder content versus correlated Marshall Stability
Binder content versus Marshall Flow
Binder content versus Percent of Void (Vv) in the total mix
Binder content versus voids filled with bitumen (VFB)
Binder content versus unit weight or bulk specific gravity (Gm)

 
Determine optimum binder content
Determine the optimum binder content for the mix design by taking average value of the following three bitumen contents found from the graphs obtained in the previous step:
Binder content corresponding to maximum correlated Marshall Stability
Binder content corresponding to maximum unit weight or bulk specific gravity (Gm)
Binder content corresponding to the median of designed limits of Percent air Void (Vv) in the total mix (i.e. 4%)
The For next trail bitumen content is varied by +0.5% and the above procedure are repeated. Number of trials is predetermined. The prepared mould is loaded in the Marshall test setup has shown in figure.
Results:
The optimum binder content is ……………
Application:
Marshall Stability test is essential to determine the percentage of binder content before making any hot-mixed asphalt concrete roads.
Observation Sheet

Conclusion and Remarks: