Civil v Transportation Engineering Unit 1,2,3,4,5,6,7,8

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VTU

Civil Engineering

5 Semester

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Transportation Engineering - 1 [10CV56]

2010 Scheme

Branch Name: Civil Engineering SEM: 5 University: VTU Syllabus: 2010

Table of Contents:

Transportation Engineering - 1 (10CV56):

Sl. No. Units 1 Principles of transportation engineering 2 Highway development and planning 3 Highway alignment and surveys 4 Highway geometric design-I 5 Highway geometric design-II 6 Pavement materials 7 Pavement design 8 Highway economics

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TRANSPORTATION ENGINEERING-I 10CV56

Page 1

TRANSPORTATION ENGINEERING I

Subject Code: 10CV56

No. of lecture Hours/week: 04

Total No. of Lecture Hours: 52

I A Marks : 25

Exam Hours : 03

Exam Marks : 100

UNIT – 1

PART – A

PRINCIPLES OF TRANSPORTATION ENGINEERING:

Importance of transportation, Different modes of transportation and comparison,

Characteristics of road transport Jayakar committee recommendations, and implementation –

Central Road Fund, Indian Roads Congress, Central Road Research Institute

04 Hrs

UNIT – 2

HIGHWAY DEVELOPMENT AND PLANNING:

Road types and classification, road patterns, planning surveys, master plan – saturation

system of road planning, phasing road development in India, problems on best alignment

among alternate proposals Salient Features of 3rd and 4th twenty year road development plans

and Policies, Present scenario of road development in India (NHDP & PMGSY) and in

Karnataka (KSHIP & KRDCL) Road development plan - vision 2021.

06 Hrs

UNIT – 3

HIGHWAY ALIGNMENT AND SURVEYS:

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Ideal Alignment, Factors affecting the alignment, Engineering surveys-Map study,

Reconnaissance, Preliminary and Final location & detailed survey, Reports and drawings for

new and re-aligned projects

04 Hrs

HIGHWAY GEOMETRIC DESIGN – I:

Importance, Terrain classification, Design speed, Factors affecting geometric design, Cross

sectional elements-Camber- width of pavement- Shoulders-, Width of formation- Right of

way, Typical cross-sections 05 Hrs

UNIT – 4

HIGHWAY GEOMETRIC DESIGN – II:

Sight Distance- Restrictions to sight distance- Stopping sight distance- Overtaking sight

distance- overtaking zones- Examples on SSD and OSD- Sight distance at intersections,

Horizontal alignment-Radius of Curve- Super elevation – Extra widening- Transition curve

and its length, setback distance – Examples, Vertical alignment-Gradient-summit and valley

curves with examples.

07 Hrs

PART - B

UNIT – 5

PAVEMENT MATERIALS:

Subgrade soil – desirable properties-HRB soil classification-determination of CBR and

modulus of subgrade reaction-Examples on CBR and Modulus of subgrade reaction,

Aggregates- Desirable properties and list of tests, Bituminous materials-Explanation on Tar,

bitumen, cutback and emulsion-List of tests on bituminous materials.

06 Hrs



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UNIT – 6

PAVEMENT DESIGN:

Pavement types, component parts of flexible and rigid pavements and their functions, design

factors, ESWL and its determination-Examples, Flexible pavement- Design of flexible

pavements as per IRC;37-2001-Examples, Rigid pavement- Westergaard‟s equations for load

and temperature stresses- Examples- Design of slab thickness only as per IRC:58-2002

06 Hrs

UNIT – 7

PAVEMENT CONSTRUCTION:

Earthwork –cutting-Filling, Preparation of subgrade, Specification and construction of i)

Granular Sub base, ii) WBM Base, iii) WMM base, iv) Bituminous Macadam, v) Dense

Bituminous Macadam vi) Bituminous Concrete, vii) Dry Lean Concrete sub base and PQC

viii) concrete roads 05 Hrs

HIGHWAY DRAINAGE:

Significance and requirements, Surface drainage system and design-Examples, sub

surfacedrainage system, design of filter materials

03 Hrs

UNIT – 8

HIGHWAY ECONOMICS:

Highway user benefits, VOC using charts only-Examples, Economic analysis - annual cost

method-Benefit Cost Ratio method-NPV-IRR methods- Examples, Highway financing-BOT-

BOOT concepts

06 Hrs



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TEXT BOOKS:

1. Highway Engineering – S K Khanna and C E G Justo, Nem Chand Bros, Roorkee

2. Highway Engineering - L R Kadiyali, Khanna Publishers, New Delhi

3. Transportation Engineering – K P Subramanium, Scitech Publications, Chennai

4. Transportation Engineering – James H Banks, Mc. Graw. Hill Pub. New Delhi

5. Highway Engineeering –R. Sreenivasa Kumar, University Press. Pvt.Ltd. Hyderabad

REFERENCE BOOKS:

1. Relevant IRC Codes

2. Specifications for Roads and Bridges-MoRT&H, IRC, New Delhi.

3. Transportation Engineering – C. Jotin Khisty, B.



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LIST OF CONTENTS

UNIT-I PRINCIPLES OF TRANSPORTATION ENGINEERING-I........................... 10

INTRODUCTION ........................................................................................ ................... 10

IMPORTANCE OF TRANSPORTATION..................................................................... . 11

DIFFERENT MODES OF TRANSPORTATION............................................................ 13

CHARACTERISTICS AND COMPARISON OF DIFFERENT MODES ....................... 15

JAYAKAR COMMITTEE RECOMMENDATIONS AND IMPLEMENTATION ......... 17

Central Research Fund (CRF): ........................................................................................ . 18

Indian Road Congress (IRC):.......................................................................................... . 18

Central Road Research Institute (CRRI): ......................................................................... 19

UNIT-2 HIGHWAY DEVELOPMENT AND PLANNING ............................................ 19

INTRODUCTION .......................................................................................................... . 19

CLASSIFICATION OF ROADS: .................................................................................... 21

ROAD PATTERNS:....................................................................................................... . 23

PLANNING SURVEYS:............................................................................. .................... 24

MASTER PLAN: ............................................................................................................ 26

SATURATION SYSTEM: ...................................................................................... ........ 27

ROAD DEVELOPMENT IN INDIA:............................................................................. . 28

Unit 3 Highway alignment ................................................................................................ 32



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Alignment ...................................................................................................................... . 32

Requirements.................................................................................... ............................... 32

Factors controlling alignment .......................................................................................... 32

UNIT 4 HIGHWAY GEOMETRIC DESIGN I & II ........................................................ 34

Introduction ..................................................................................................................... 35

Factors affecting geometric design.................................................................................. . 35

Camber........................................................................................................................... . 37

Width of carriage way ............................................................................................. ........ 38

Kerbs............................................................................................................................. .. 38

Road margins ............................................................................................. ..................... 39

Shoulders........................................................................................................................ . 39

Parking lanes ................................................................................................................... 39

Bus-bays......................................................................................................................... . 40

Service roads ................................................................................................................... 40

Footpath .......................................................................................................................... 40

Guard rails....................................................................................................................... 40

Width of formation .......................................................................................................... 41

Right of way .................................................................................................................... 41

Sight distance .................................................................................................................. 42

Types of sight distance ................................................................................................... . 42

Stopping sight distance .................................................................................................... 44



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Overtaking sight distance................................................................................................ . 45

Overtaking zones ............................................................................................................ . 47

Horizontal curve ............................................................................................................. . 48

Analysis of super-elevation............................................................................................. . 50

Horizontal Transition Curves ........................................................................................... 53

Length of transition curve ............................................................................................... . 54

Setback Distance ............................................................................................................. 56

Vertical alignment .......................................................................................................... . 59

Gradient .......................................................................................................................... 59

Summit curve .................................................................................................................. 60

Valley curve .................................................................................................................... 62

UNIT 5 PAVEMENT MATERIALS............................................................................... . 66

Introduction ..................................................................................................................... 66

Subgrade soil ................................................................................................................... 66

Desirable Properties........................................................................................................ . 67

Soil classification ............................................................................................................ 67

2. Highway Research Board (HRB) classification of soils................................................ 67

California Bearing Ratio (CBR) Test ............................................................................... 69

AGGREGATES .............................................................................................................. 75

Tests for Road Aggregate ................................................................................................ 76

BITUMINOUS MATERIALS ......................................................................................... 77



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Types of Bituminous Materials ........................................................................................ 77

Tests on Bitumen............................................................................................................ . 78

Bituminous Emulsion ..................................................................................................... . 80

BITUMINOUS PAVING MIXES ................................................................................... 83

Unit 6 Introduction to pavement design .......................................................................... . 85

Requirements of a pavement ........................................................................................... . 85

Types of pavements ......................................................................................................... 85

Flexible pavements ......................................................................................................... . 85

Rigid pavements .............................................................................................................. 87

Types of Rigid Pavements .............................................................................................. . 87

Factors affecting pavement design ................................................................................... 88

IRC method of design of flexible pavements.................................................................... 92

Rigid pavement design ................................................................................................... . 95

Wheel load stresses - Westergaard's stress equation ......................................................... 95

UNIT 7 HIGHWAY CONSTRUCTION......................................................................... . 98

Introduction ..................................................................................................................... 98

EARTHWORK .............................................................................................................. . 99

CONSTRUCTION OF EARTH ROADS.............................................................. ......... 102

CONSTRUCTION OF GRAVEL ROADS .................................................................... 104

CONSTRUCTION OF WATER BOUND MACADAM ROADS.................................. 105

CONSTRUCTION OF BITUMINOUS PAVEMENTS ................................................. 109



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Construction Procedure for Bituminous Concrete .......................................................... 115

HIGHWAY DRAINAGE..................................................................... ........................... 123

INTRODUCTION ........................................................................................................ . 123

IMPORTANCE OF HIGHWAY DRAINAGE .............................................................. 123

UNIT 8 HIGHWAY ECONOMICS & FINANCE ........................................................ 128

INTRODUCTION ........................................................................................................ . 128

HIGHWAY USER BENEFITS ..................................................................................... 129

Annual Highway Cost................................................................................................... . 131

HIGHWAY FINANCE ................................................................................................. 136

Highway financing in India........................................................................................... . 138



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UNIT-I PRINCIPLES OF TRANSPORTATION

ENGINEERING-I

INTRODUCTION

Basic Definition: A facility consisting of the means and equipment necessary for the

movement of passengers or goods. At its most basic, the term “transportation system” is used

to refer to the equipment and logistics of transporting passengers and goods. It covers

movement by all forms of transport, from cars and buses to boats, aircraft and even space

travel. Transportation systems are employed in troop movement logistics and planning, as

well as in running the local school bus service.

Function: The purpose of a transportation system is to coordinate the movement of people,

goods and vehicles in order to utilize routes most efficiently. When implemented,

transportation systems seek to reduce transport costs and improve delivery times through

effective timetabling and route management. Periodic re-evaluations and the development of

alternative routes allow for timely changes to the transportation system in order to maintain

efficiency.

Features: A standard transportation system will usually feature multiple timetables designed

to inform the user of where each vehicle in the fleet is expected to be at any given point in

time. These timetables are developed alongside an array of route plans designed to coordinate

vehicle movements in a way that prevents bottlenecks in any one location.

Benefits: The main benefit of implementing a transportation system is delivery of goods and

personnel to their destinations in a timely manner. This in turn increases the efficiency of

vehicle use, as the same vehicle can be used for “multi-drop” jobs, such as bus services or

home delivery networks, far more effectively when their routes are planned in advance rather

than being generated “on the fly.”

Size: Transportation systems are developed in a wide variety of sizes. Local transport

networks spanning the bus network for a city and its suburbs are common, as are country-



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wide delivery networks for haulage firms. Airlines use international transportation systems to

coordinate their flights. The larger the distance being covered, the more effective the use of

vehicles when a transportation system is used.

IMPORTANCE OF TRANSPORTATION

The world that we live in now will most likely be impossible had it not been for

innovations in transportation. There would not have been any great infrastructure,

industrialisation, or massive production, if transportation was incompetent. Life would not

have kept up with the fast changing times if there were no huge trucks, bulldozers, trailers,

cargo ships, or large aircrafts to carry them to different places. In other words, the global

society would not have experienced comfort and convenience had it not been for

advancements in the transportation sector. Today, humanity has technology to thank for all

the wonderful things that it currently enjoys now.

Transportation is vital for the economic development of any region since every

commodity produced whether it is food, clothing, industrial products or medicine needs

transport at all stages from production to distribution. In the production stage transportation is

required for carrying raw materials like seeds, manure, coal, steel etc. In the distribution stage

transportation is required from the production centres viz; farms and factories to the

marketing centres and later to the retailers and the consumers for distribution.

The transportation has lots of advantages and even disadvantages. The more focus is

on advantages as we cannot think about the life without transportation. The importance of

transportation may include:

x Availability of raw materials: Transportation helps in carrying the raw materials

from one place to another place. Initially raw materials are made at one place and are

being transported to another place for processing and for manufacturing goods.

x Availability of goods to the customer: The goods are being transported from one

place to another place. These goods which are produced at one place are transported



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to other distant places for their usage. It flexibly moves the goods from one place to

another place.

x Enhances the Standard Of Living: It improves the standard of living. As the

transportation of each and every good is being done then the productivity increases

which results in the reduced or the effective costs. Because of reduction in the cost

they can use different commodities for different purposes and can lead a secure life.

x Helps a lot during the emergencies and even during natural disasters:

Transportation helps during the natural disturbances. It helps in quick moving from

one place to another place and supplies the required operations.

x Helps for the employment: Transportation provides employment for many people as

drivers, captains, conductors, cabin crew and even the people are used for the

construction of different types of transportation vehicles. And even by the use of

transportation the remote people are being employed with the access to the urban

facilities and the opportunities.

x Helps in mobility of the laborers: Many people are traveling to other countries on

their employment basis. Transportation plays an important role in such cases.

x Helps for bringing nations together: Transportation on the whole is used for

globalization i.e. it brings nations together and it creates awareness about the cultural

activities and even about the industries and helps a lot for importing and exporting of

different goods.

These above are some of the necessities which make us to use transportation.

The importance and adequacy of transportation system of a country indicates

its economic and social development.

Economic Activity: Two important factors well known in economic activity are:

x Production or supply and

x Consumption for human wants or demand.

Social Effects: The various social effects of transportation may be further classified into:



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x Sectionalism and transportation

x Concentration of population into urban area

x Aspect of safety, law and order.

DIFFERENT MODES OF TRANSPORTATION

Three basic modes of transport are by land, water and air. Land has given

development of road and rail transport. Water and air have developed waterways and airways

respectively. Apart from these major modes of transportation, other modes include pipelines,

elevators, belt conveyors, cable cars, aerial ropeways and monorails. Pipe lines are used for

the transportation of water, other fluids and even solid particles

The four major modes of transportation are:

x Roadways or highways

x Railways

x Airways

x Waterways.

Airways:

x The transportation by air is the fastest among the four modes.

x Air also provides more comfort apart from saving in transportation time for the

passengers and the goods between the airports.

Waterways:

x Transportation by water is the slowest among the four modes.

x This mode needs minimum energy to haul load through unit distance



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x The transportation by water is possible between the ports on the sea routes or along

the rivers or canals where inland transportation facilities are available.

Railways:

x The transportation along the railway track could be advantageous by railways

between the stations both for the passengers and goods, particularly for longer

distances.

x The energy requirement to haul unit load through unit distance by the railway is only

a fraction (one fourth to one sixth) of the required by road.

x Hence, full advantage of this mode of transportation should be taken for the

transportation of bulk goods along land where the railway facilities are available.

Roadways:

x The transportation by road is the only mode which could give maximum service to

one and all.

x The road or highways not only include the modern highway system but also the city

streets, feeder roads and village roads, catering for a wide-range of road vehicles and

the pedestrians.

x This mode has also maximum flexibility for travel with reference to route, direction,

time and speed of travel etc. through any mode of road vehicle.

x It is possible to provide door to door service by road transport.

x The other three modes (railways; water ways; airways) has to depend on the roadway

for the service.

x Ultimately, road network is therefore needed not only to serve as feeder system for

other modes of transportation and to supplement them, but also to provide

independent facility for road travel by a well planned network of roads throughout

the country.



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CHARACTERISTICS AND COMPARISON OF DIFFERENT MODES

It is accepted that the fact road transport is the nearest to the people. The passengers

and goods have to be first transported by road before reaching a railway station or an airport.

It is seen that road network alone could serve the remotest villages of the vast country like

occurs.

The various characteristics (advantages) and disadvantages of different mode of transport are

briefly listed here:

Roadways:

Advantages:

x Flexibility: It offers complete freedom to the road users.

x It requires relatively smaller investments and cheaper in construction with respect to

other modes.

x It serves the whole community alike the other modes.

x For short distance travel it saves time.

x These are used by various types of vehicles.

Disadvantages:

x Speed is related to accidents and more accidents results due to higher speed.

x Not suitable for long distance travel

x Power required per tonne is more.

Railways:

Advantages:

x Can transport heavy loads of goods at higher speed



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x Power required per tonne is less compared to roadways

x Chances of accidents are less.

Disadvantages:

x Entry and exist points are fixed

x Requires controlling system and no freedom of movement

x Establishment and maintenance cost is higher.

Waterways:

Advantages:

x Cheapest: Cost per tonne is lowest

x Possess highest load carrying capacity

x Leads to the development of the industries.

Disadvantages:

x Slow in operation and consumes more time

x Depends on weather condition

x Chances of attack by other countries on naval ships are more.

x Ocean tides affects the loading and unloading operation

x The route is circuitous.

Airways:

Advantages:

x It has highest speed



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x Intercontinental travel is possible

x Journey is continuous over land and water

Disadvantages:

x Highest operating cost (cost/tonne is more)

x Load carrying capacity is lowest

x Depends on weather condition

x Should follow the flight rules.

JAYAKAR COMMITTEE RECOMMENDATIONS AND IMPLEMENTATION

RECOMMENDATIONS: Over a period after the First World War, motor vehicles using the

roads increased and this demanded a better road network which can carry mixed traffic

conditions. The existing roads when not capable to withstand the mixed traffic conditions.

For the improvement of roads in India government of India appointed Mr. Jayakar Committee

to study the situations and to recommend suitable measures for road improvement in 1927

and a report was submitted in 1928 with following recommendations:

x Road development in the country should be considered as a national interest. As the

provincial and local government do not have the financial and technical capacity for

road development.

x Extra tax to be levied from the road users as fund to develop road.

x A Semi-official technical body has to be formed to collect and pool technical

knowhow from various parts of the country and to act as an advisory body on various

aspects of the roads.

x A research organisation should be instituted at National level to carry out research and

development work and should be available for consultation.



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IMPLEMENTATIONS:

Majority of the recommendations were accepted by the government implemented by

Jayakar Committee.

Some of the technical bodies were formed such as,

• Central Road Fund (CRF) in 1929

• Indian Road Congress (IRC) in 1934

• Central Road Research Institute (CRRI) in 1950.

Central Research Fund (CRF):

x Central Research Fund (CRF) was formed on 1st

March 1929

x The consumers of petrol were charged an extra leavy of 2.64 paisa/litre of petrol to

buildup this road development fund.

x From the fund collected 20 percent of the annual revenue is to be retained as meeting

expenses on the administration of the road fund, road experiments and research on

road and bridge projects of special importance.

x The balance 80 percent of the fund to be allotted by the Central Government to the

various states based on actual petrol consumption or revenue collected

x The accounts of the CRF are maintained by the Accountant General of Central

Revenues.

x The control of the expenditure is exercised by the Roads Wings of Ministry of

Transport.

Indian Road Congress (IRC):

x It is a semi-official technical body formed in 1934.



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x It was formed to recommend standard specifications.

x It was constituted to provide a forum of regular technical pooling of experience and

ideas on all matters affecting the planning, construction and maintenance of roads in

India.

x IRC has played an important role in the formulation of the 20-year road development

plans in India.

x Now, it has become an active body of national importance controlling specifications,

guidelines and other special publications on various aspect of Highway Engineering.

Central Road Research Institute (CRRI):

x CRRI was formed in the year 1950 at New Delhi

x It was formed for research in various aspect of highway engineering

x It is one of the National laboratories of the Council of Scientific and Industrial

Research.

x This institute is mainly engaged in applied research and offers technical advice to

state governments and the industries on various problems concerning roads.



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UNIT-2 HIGHWAY DEVELOPMENT AND PLANNING

INTRODUCTION

Highway design is only one element in the overall highway development process.

Historically, detailed design occurs in the middle of the process, linking the preceding phases

of planning and project development with the subsequent phases of right-of-way acquisition,

construction, and maintenance. While these are distinct activities, there is considerable

overlap in terms of coordination among the various disciplines that work together, including

designers, throughout the process.

It is during the first three stages, planning, project development, and design, that designers

and communities, working together, can have the greatest impact on the final design features

of the project. In fact, the flexibility available for highway design during the detailed design

phase is limited a great deal by the decisions made at the earlier stages of planning and

project development. This Guide begins with a description of the overall highway planning

and development process to illustrate when these decisions are made and how they affect the

ultimate design of a facility.



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Meaning of Highway and Road:

Road: A road is a thoroughfare, route or way on land between two places, which typically

has been paved or otherwise improved to allow travel by some conveyance, including a

horse, cart, or motor vehicle.

Highway: A highway is a public road, especially a major road connecting two or more

destinations. Any interconnected set of highways can be variously referred to as a "highway

system", a "highway network", or a "highway transportation system". Each country has its

own national highway system.

TYPES OF ROAD:

Basically, different types of roads can be classified into two categories namely,

x All-weather roads and

x Fair-weather roads.

All-weather roads: These roads are negotiable during all weather, except at major river

crossings where interruption of traffic is permissible upto a certain limit extent, the road

pavement should be negotiable during all weathers.

Fair-weather roads: On these roads the traffic may be interrupted during monsoon season at

causeways where streams may overflow across the roads.

CLASSIFICATION OF ROADS:

Roads are classified based on various aspects namely,

1) Based on the carriage way,

x Paved Roads: These roads are provided with a hard pavement course which should be

atleast a water bound macadam (WBM) layer.

x Unpaved Roads: These roads are not provided with a hard pavement course of atleast

a WBM layer. Thus earth roads and gravel roads may be called as unpaved roads.



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2) Based on Surface pavement provided,

x Surface Roads: These roads are provided with a bituminous or cement concrete

surfacing.

x Unsurfaced

surfacing.

Roads: These are not provided with bituminous or cement concrete

x Roads which are provided with bituminous surfacing are called as black toped roads

and that of concrete are referred to as concrete roads respectively.

3) Based on Traffic Volume:

x Heavy

x Medium

x Light traffic roads.

4) Based on Load transported or tonnage:

x Class-I or Class-A

x Class-II or Class-B.

5) Based on location and Function:

x National Highways (NH): The NH connects the capital cities of the states and the

capital cities to the port. The roads connecting the neighbouring countries are also

called as NH. The NH are atleast 2 lanes of traffic about 7.5m d wide. The NH are

having concrete or bituminous surfacing.

x State Highways (SH): SH are the main roads within the state and connect important

towns and cities of state. The width of state highways is generally 7.5m.

x Major District Roads (MDR): These roads connect the areas of production and

markets with either a SH or railway. The MDR should have atleast metalled single

lane carriage way (i.e., 3.8m) wide. The roads carry mixed traffic.



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x Other District Roads (ODR): these roads connect the village to other village or the

nearest district road, with ghat, river etc. these roads have a single lane and carry

mixed traffic.

x Village Roads (VR): these roads, like other district roads, connect the village or

village or nearby district road. The roads carry mixed traffic.

6) Modified Classification of Road system by Third Road Development Plan:

x Primary System (Expressways and National Highways)

x Secondary System (State Highways and Major District Roads)

x Tertiary System (Other District Roads and Village Roads).

7) Based on Urban Roads:

x Arterial roads

x Sub-arterial roads

x Collector Streets

x Local Streets

Arterial and Sub-arterial roads are primarily for through traffic on a continuous route,

but 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

from and to local streets which provide access to abutting property.

ROAD PATTERNS:

There are various types of road patterns and each pattern has its own advantages and

limitations. The choice of the road pattern depends upon the various factors such as:

x Locality

x Layout of the different towns, villages, industrial and production centres.



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x Planning Engineer.

The various road patterns may be classified as follows:

x Rectangular or block pattern: In this, entire area is divided into rectangular

segments having a common central business and marketing area. This area has all the

services located in the central place. This pattern is not convenient or safe from traffic

operation point of view and it results into more number of accidents at intersections.

Eg: Chandigarh city.

x Radial or star and block pattern: In this, roads radially emerge from the central

business area in all directions and between two built-up area will be there. The main

advantage in this, central place is easy accessible from all the directions. Eg: Nagpur

x Radial or star and circular pattern: In this roads radiate in all the directions and

also circular ring roads are provided.

Advantages: Traffic will not touch the heart of the city and it flows radially and

reaches the other radial road and thereby reducing the congestion in the centre of the

city. This ring road system is well suited for big cities where traffic problems are

more in the heart of the city. Eg: Connaught place in New Delhi.

x Radial or star and grid pattern: It is very much similar to star and the circular

pattern expects the radial roads are connected by grids. In this pattern a grid is formed

around the central point which is a business centre. Eg: Nagpur road plan.

x Hexagonal pattern: In this entire zone of planning is divided into hexagonal zones

having separate marketing zone and central services surrounded by hexagonal pattern

of roads. Each hexagonal element is independent. At each corner of hexagon three

roads meet.

x Minimum travel pattern: In this type, city is divided into number of nodal points

around a central portion by forming sectors. And each sector is divided again in such

a way that from each of the nodal centre, the distance to the central place is minimum.

PLANNING SURVEYS:



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Prior to the development of highways planning is required for any engineering

works, which is a basic requirement for a new project or for an expansion. In all

developing countries like India where, the resources are limited and requirement is

high then planning provides better utilization of funds in a system.

Objective of Planning surveys:

x Workout, the financial system and recommended changes in tax arrangements and

budget procedures, provide efficient, safe economics, comfortable and speedy

movement for goods and people.

x Plan a road network for efficient traffic operation at minimum cost.

x Plan for future requirements and improvements of roads in view of developments and

social needs.

x Fix up datawise priorities for development of each road link based on their utilities.

The planning surveys consist of the following studies:

x Economic Studies: This study consists the following details:

Population and its distribution

Trend of population growth

Age and land products

Existing facilities

Per Capita income.

x Financial Studies: This study involves collecting the details such as:

Sources of income

Living Standards

Resources from local levels

Factor trends in financial.

x Traffic or road use studies: In this details collected are:

Traffic Volume/day, annual or daily traffic peak flow.



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Origin and destination studies

Traffic flow patterns

Mass transportation facilities

Accidents, cause and cost analysis.

x Engineering studies: This involves:

Topographic study

Soil details

Location and classification of existing roads

Road life studies

Specific problems in drainage constructions and maintenance.

MASTER PLAN:

Master plan is refered to as road development plan of a city; district or a street or for

whole country. It is an ideal plan showing full development of the area at some future date. It

serves as the guide for the plan to improve some of the existing roads and to plan the network

of new roads.

It helps in controlling the industrial, commercial and agricultural and habitat growth

in a systematic way of that area. It gives a perceptive picture of a fully developed area in a

plan and scientific way.

Stages in the preparation of master plan:

x Data Collection: It includes data regarding existing land use, industrial and

agricultural growth, population, traffic flow, topography, future trends.

x Preparation of

experts.

draft plan and invite suggestions and comments from public and

x Revision of draft plan in view of the discussions and comments from experts and

public.

x Comparison of various alternate proposals of road system and finding out the

sequence in which the master plan will be implemented.



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In India targeted road lengths were fixed in various road plans, based on

population, area and agricultural and industrial products. The same way it may be taken as a

guide to decide the total length of road system in each alternate proposal while preparing a

master plan for a town or locality.

Preparation of Plans:

x Plan-1: This plan should give the topographical details related to existing road

network, drainage, structures, towns and villages with population, agricultural,

industrial and commercial activities.

x Plan-2: Should give the details pertaining to the distribution of population

x Plan-3: Should indicate the location of places with productivity.

x Plan-4: Should indicate the existing network of roads and proposals received.

Ultimately, the Master plan is the one to be implemented.

SATURATION SYSTEM:

In this system optimum road length is calculated for an area based on the concept of

attaining maximum utility per unit length of the road. This is also called as maximum utility

system.

Factors to attain maximum utility per unit length are:

x Population served by the road network

x Productivity (industrial and agricultural) served by the road network.

The various steps to be taken to obtain maximum utility per unit length are:

x Population factors or units: Since, the area under consideration consists of villages

and towns with different population these are grouped into some convenient

population range and some reasoning values of utility units to each range of

population serve are assigned.

Population less than 500, utility unit = 0.25

501 to 1001, utility unit = 0.50



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1001 to 2000, utility unit = 1.00

2001 to 5000, utility unit = 2.00 etc.

x Productivity Factors or units: The total agricultural and industrial products served

by each road system are worked out and the productivity served may be assigned

appropriate values of utility units per unit weight.

x Optimum Road length: Based on the master plan the targeted road length is fixed for

the country on the basis of area or population and production or both. And the same

may be taken as a guide to decide the total length of the road system in each

proposal.

ROAD DEVELOPMENT IN INDIA:

The first attempt for proper planning of the highway development programme in India

on a long term basis was made at the Nagpur Conference in 1943. After, the completion of

the Nagpur Road Plan targets, the Second Twenty year Plan was drawn for the period 1961-

1981. The Third Twenty Year Road Development Plan for the period 1981-2001 was

approved only by the year 1984.

First 20-Year Road Plan (Nagpur Road plan):

This plan was formed in the year 1943 at Nagpur. The plan period was from 1943-

1963.Two plan formulae were finalized at the Nagpur Conference for deciding two categories

of road length for the country as a whole as well as for individual areas (like district). This

was the first attempt for highway planning in India. The two plan formulae assumed the Star

and Grid pattern of road network. Hence, the two formulae are also called “Star and Grid

Formulae”.

Salient Features of Nagpur Road Plan:

x The roads are classified as,

Primary System (NH/Expressways)

Secondary System (SH/MDR)



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Tertiary System(ODR/VR)

x Construction and Maintenance of NH was assigned to Central government

x It aims for 2, 00,000km of bituminous road and 3, 32,700km of other types.

x The formulae was based on star and grid pattern of road network and was considered

as two equations:

I –Category: NH/SH/MDR

II-Category: ODR/VR

x NH/SH/MDR are meant to provide main grids and ODR/VR as internal road system

x The development allowance is 15%

x The length of railway track was deducted.

Second Twenty Year Road Plan (Bombay Road Plan):

As the target road length of Nagpur road plan was completed nearly earlier in

1961 a long term plan was initiated for twenty year period which was initiated by IRC.

Hence, the second twenty year road plan came into picture which was drawn for the

period of 1961-81. The second twenty year road plan was envisaged overall road length

of 10, 57,330 km by the year 1981.

Salient Features of Second 20 year Road Plan:

x Aim to provide 32km/100 sqkm area

x Every town with population above 2000 in plains should be connected by a

bituminous road or mettaled road.

>2000 in plains

>1000 in semi-hill area

>500 in hilly area

x 1600 km length of expressways was proposed

x Development allowance is 5% only

x Length of railway track was not deducted.

x Five equations are given to find NH/SH/MDR/ODR/VR.



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Comparison of I and II 20-year plans:

First 20-year Plan Second 20-year Plan

x Areas is divided into two types Areas is divided into three types

namely, developed and semi-developed namely, developed; semi-

developed areas

x Two equations are given to find

NH/SH/MDR/ODR/VR

x Aim is 16km/100 sqkm

x Development allowance is 15%

x No express ways

x Length of Railway track was deducted

and undeveloped area.

Five equations are given to find

NH/SH/MDR/ODR/VR. Aim

is 32km/100 sqkm.

Development allowance is 5%.

1600km of expressway was

included.

Not deducted.

Third Twenty Year Road Plan (Lucknow Road Plan):

The third twenty year road plan was prepared by the Road Wing of the

Ministry of Shipping and Transport with the active co-operation from a number of

organisations and the experts in the field of Highway Engineering and Transportation.

This document was released during the 45th

Annual Session and the Golden Jubilee

celebrations of the Indian Road Congress in February 1985 at Lucknow. Therefore, this

plan for 1981-2001 is also called as „Lucknow Road Plan‟.

Salient Features of Second 20 year Road Plan:

x Road development is based on the primary, secondary and tertiary road system

x All the villages with the population above 500 is to be connected with the metalled

road

x Aim is 82km/100 sq km

x NH will form the main guideline

x The length of SH and MDR are calculated based on the area of population



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x Town >1500 –MDR

1000-1500 –ODR

x Roads should also be built in less industrialized area

x Long term master plans should be prepared at taluk, district and state levels

x Existing roads should be improved

x There should be improved environmental quality and road safety.



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Unit 3 Highway alignment

Alignment

The position or the layout of the central line of the highway on the ground is called

the alignment. Horizontal alignment includes straight and curved paths. Vertical alignment

includes level and gradients. Alignment decision is important because a bad alignment will

enhance the construction, maintenance and vehicle operating cost. Once an alignment is fixed

and constructed, it is not easy to change it due to increase in cost of adjoining land and

construction of costly structures by the roadside

Requirements

The requirements of an ideal alignment are

x The alignment between two terminal stations should be short and as far as possible be

straight, but due to some practical considerations deviations may be needed.

x The alignment should be easy to construct and maintain. It should be easy for the

operation of vehicles. So to the maximum extend easy gradients and curves should be

provided.

x It should be safe both from the construction and operating point of view especially at

slopes, embankments, and cutting. It should have safe geometric features.

x The alignment should be economical and it can be considered so only when the initial

cost, maintenance cost, and operating cost is minimum.

Factors controlling alignment



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We have seen the requirements of an alignment. But it is not always possible to satisfy al

these requirements. Hence we have to make a judicial choice considering all the factors.

The various factors that control the alignment are as follows:

x Obligatory points these are the control points governing the highway alignment.

These points are classified into two categories. Points through which it should pass

and points through which it should not pass. Some of the examples are:

{Bridge site: The bridge can be located only where the river has straight and

permanent path and also where the abutment and pier can be strongly founded. The

road approach to the bridge should not be curved and skew crossing should be

avoided as possible. Thus to locate a bridge the highway alignment may be changed.

{Mountain: While the alignment passes through a mountain, the various alternatives

are to either

Construct a tunnel or to go round the hills. The suitability of the alternative depends

on factors like topography, site conditions and construction and operation cost.

{Intermediate town: The alignment may be slightly deviated to connect an

intermediate town orvillage nearby. These were some of the obligatory points through

which the alignment should pass. Coming to the second category, that is the points

through which the alignment should not pass are:

{religious places: These have been protected by the law from being acquired for any

purpose. Therefore, these points should be avoided while aligning.

{Very costly structures: Acquiring such structures means heavy compensation which

would result in an increase in initial cost. So the alignment may be deviated not to

pass through that point.

{Lakes/ponds etc: The presence of a lake or pond on the alignment path would also

necessiate deviation of the alignment.



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x Traffic: The alignment should suit the tra_c requirements. Based on the origin-

destination data of the area, the desire lines should be drawn. The new alignment

should be drawn keeping in view the desire lines, traffic flow pattern etc.

x Geometric design: Geometric design factors such as gradient, radius of curve, sight

distance etc. also governs the alignment of the highway. To keep the radius of curve

minimum, it may be required to change the alignment of the highway. The alignments

should be finalized such that the obstructions to visibility do not restrict the minimum

requirements of sight distance. The design standards vary with the class of road and

the terrain and accordingly the highway should be aligned.

x Economy: The alignment finalized should be economical. All the three costs i.e.

construction, maintenance, and operating cost should be minimum. The construction

cost can be decreased much if it is possible to maintain a balance between cutting and

filling. Also try to avoid very high embankments and very deep cuttings as the

construction cost will be very higher in these cases.

x Other considerations: various other factors that govern the alignment are drainage

considerations, political factors and monotony.



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UNIT 4 HIGHWAY GEOMETRIC DESIGN I & II

Introduction

The geometric design of highways deals with the dimensions and layout of visible

features of the highway. The emphasis of the geometric design is to address the requirement

of the driver and the vehicle such as safety, comfort, efficiency, etc. The features normally

considered are the cross section elements, sight distance consideration, horizontal curvature,

gradients, and intersection.

Factors affecting geometric design

Factors affecting the geometric designs are as follows

x Design speed:

o Design speed is the single most important factor that affects the geometric design. It

directly affects the sight distance, horizontal curve, and the length of vertical curves.

Since the speed of vehicles vary with driver, terrain etc, a design speed is adopted for

all the geometric design.

x Topography:

o It is easier to construct roads with required standards for a plain terrain. However, for

a given design speed, the construction cost increases multi form with the gradient and

the terrain.

x Traffic:

x It will be uneconomical to design the road for peak traffic flow. Therefore a reasonable

value of traffic volume is selected as the design hourly volume which is determined from

the various traffic data collected



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x Environmental:

o Factors like air pollution, noise pollution etc. should be given due consideration in the

geometric design of roads.

x Economy:

o The design adopted should be economical as far as possible. It should match with the

funds allotted for capital cost and maintenance cost.

x Others:

o Geometric design should be such that the aesthetics of the region is not affected

Cross sectional elements

The feature of the cross-section of the pavement influences the life of the pavement as well

as the riding comfort and safety.

Pavement surface characteristics

For a

important;

Friction

safe and comfortable driving four aspects of the pavement surface are

Friction between the wheel and the pavement surface is a crucial factor in the design

of horizontal curves and thus the safe operating speed. Further, it also affects the acceleration

and deceleration ability of vehicles. Lack of adequate friction can cause skidding or slipping

of vehicles.

Various factors that affect friction are:

x Type of the pavement (like bituminous, concrete, or gravel),

x Condition of the pavement (dry or wet, hot or cold, etc),

x Condition of the tire (new or old), and

x Speed and load of the vehicle.



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The choice of the value of f is a very complicated issue since it depends on many variables.

IRC suggests the coefficient of longitudinal friction as 0.35-0.4 depending on the speed and

coefficient of later friction as 0.15.

Unevenness

It affects the vehicle operating cost, speed, riding comfort, safety, fuel consumption

and wear and tear of tires. Unevenness index is a measure of unevenness which is the

cumulative measure of vertical undulation of the pavement surface recorded per unit

horizontal length of the road.

Light reaction

x White roads have good visibility at night, but caused glare during day time.

x Black roads has no glare during day, but has poor visibility at night

.

Drainage

The pavement surface should be absolutely impermeable to prevent seepage of water

into the pavement layers.

Camber

Camber or cant is the cross slope provided to raise middle of the road surface in the

transverse direction to drain off rain water from road surface.

The objectives of providing camber are:

x Surface protection especially for gravel and bituminous roads

x Sub-grade protection by proper drainage

x Quick drying of pavement which in turn increases safety

Too steep slope is undesirable for it will erode the surface. Camber is measured in 1 in n or

n% (Eg. 1 in 50 or2%) and the value depends on the type of pavement surface.



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Figure: Lane width for single and two lane roads

Width of carriage way

Width of the carriage way or the width of the pavement depends on the width of the

traffic lane and number of lanes. Width of a traffic lane depends on the width of the vehicle

and the clearance. Side clearance improves operating speed and safety.

Kerbs

Kerbs indicate the boundary between the carriage way and the shoulder or islands or

footpaths. Different types of kerbs are (Figure 12:3):

x Low or mountable kerbs:

These types of kerbs are provided such that they encourage the traffic to remain in the

through traffic lanes and also allow the driver to enter the shoulder area with little

difficulty..

x Semi-barrier type kerbs:

When the pedestrian traffic is high, these kerbs are provided. Their height is 15 cm

above the pavement edge.



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x Barrier type kerbs:

They are designed to discourage vehicles from leaving the pavement. They are

provided when there is considerable amount of pedestrian traffic. They are placed at a

height of 20 cm above the pavement edge with a steep batter.

Submerged kerbs:

They are used in rural roads. The kerbs are provided at pavement edges between the

pavement

pavement.

edge and shoulders. They provide lateral confinement and stability to the

Road margins

The portion of the road beyond the carriageway and on the roadway can be generally

called road margin. Various elements that form the road margins are given below.

Shoulders

A shoulder are provided along the road edge and is intended for accommodation of

stopped vehicles, serve as an emergency lane for vehicles and provide lateral support for base

and surface courses. The shoulder should be strong enough to bear the weight of a fully

loaded truck even in wet conditions.

Parking lanes

Parking lanes are provided in urban lanes for side parking. Parallel parking is

preferred because it is safe for the vehicles moving in the road. The parking lane should have

a minimum of 3.0 m width in the case of parallel parking.



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Bus-bays

Bus bays are provided by recessing the kerbs for bus stops. They are provided so that

they do not obstruct the movement of vehicles in the carriage way.

Service roads

Service roads or frontage roads give access to access controlled highways like

freeways and expressways. They run parallel to the highway and will be usually isolated by a

separator and access to the highway will be provided only at selected points.

Cycle track

Cycle tracks are provided in urban areas when the volume of cycle traffic is high

Minimum width of 2 meter is required, which may be increased by 1 meter for every

additional track.

Footpath

Footpaths are exclusive right of way to pedestrians, especially in urban areas. They

are provided for the safety of the pedestrians when both the pedestrian traffic and vehicular

traffic is high.

Guard rails

They are provided at the edge of the shoulder usually when the road is on an embankment.

They serve to prevent the vehicles from running o_ the embankment, especially when the

height of the fill exceeds 3 m.



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Width of formation

Width of formation or roadway width is the sum of the widths of pavements or

carriage way including separators and shoulders. This does not include the extra land in

formation/cutting. The values suggested by IRC are given in Table

Right of way

Right of way (ROW) or land width is the width of land acquired for the road, along its

alignment. It should be adequate to accommodate all the cross-sectional elements of the

highway and may reasonably provide for future development.:

x Width of formation: It depends on the category of the highway and width of roadway and

road margins.

x Height of embankment or depth of cutting: It is governed by the topography and the

vertical alignment.

x Side slopes of embankment or cutting: It depends on the height of the slope, soil type etc.

x Drainage system and their size which depends on rainfall, topography etc.

Table: Normal right of way for open areas



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The importance of reserved land is emphasized by the following Extra width of land is

available for the construction of roadside facilities.

Figure: A typical Right of way

Sight distance

The safe and efficient operation of vehicles on the road depends very much on the

visibility of the road ahead of the driver.

Types of sight distance

Sight distance available from a point is the actual distance along the road surface, over

which a driver from a specified height above the carriage way has visibility of stationary or

moving objects. Three sight distance situations are considered for design:

x Stopping sight distance (SSD) or the absolute minimum sight distance

x Intermediate sight distance (ISD) is the defined as twice SSD

x Overtaking sight distance (OSD) for safe overtaking operation

x Head light sight distance is the distance visible to a driver during night driving under the

illumination of head light

x Safe sight distance to enter into an intersection



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The most important consideration in all these is that at all times the driver travelling at the

design speed of the highway must have sufficient carriageway distance within his line of

vision to allow him to stop his vehicle before colliding with a slowly moving or stationary

object appearing suddenly in his own traffic lane. The computation of sight distance depends

on:

x Reaction time of the driver

Reaction time of a driver is the time taken from the instant the object is visible to the

driver to the instant when the brakes are applied. The total reaction time may be split up into

four components based on PIEV theory. In practice, all these times are usually combined into

a total perception- reaction time suitable for design purposes as well as for easy

measurement.

x Speed of the vehicle

The speed of the vehicle very much affects the sight distance. Higher the speed, more time

will be required to stop the vehicle. Hence it is evident that, as the speed increases, sight

distance also increases.

x Efficiency of brakes

The efficiency of the brakes depends upon the age of the vehicle, vehicle characteristics

etc. If the brake efficiency is 100%, the vehicle will stop the moment the brakes are applied.

But practically, it is not possible to achieve 100% brake efficiency..

x Frictional resistance between the tire and the road

The frictional resistance between the tire and road plays an important role to bring the

vehicle to stop. When the frictional resistance is more, the vehicles stop immediately. Thus

sight required will be less. No separate provision for brake efficiency is provided while

computing the sight distance..

x Gradient of the road



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Gradient of the road also affects the sight distance. While climbing up a gradient, the

vehicle can stop immediately. Therefore sight distance required is less.

Stopping sight distance

SSD is the minimum sight distance available on a highway at any spot having

sufficient length to enable the driver to stop a vehicle traveling at design speed, safely

without collision with any other obstruction..

Lag distance is the distance the vehicle traveled during the reaction time t and is given by vt,

where v is the

velocity in m=sec2.

Braking distance is the distance traveled by the vehicle during braking operation. For a level

road this is obtained by equating the work done in stopping the vehicle and the kinetic energy

of the vehicle. If F is the maximum frictional force developed and the braking distance is l,

then work done against friction in stopping the vehicle is

Fl = fWl

kinetic energy at the design speed is

where W is the total weight of the vehicle. The

Therefore, the SSD = lag distance + braking distance and given by:

SSD = vt + v2

2gf

Where v is the design speed in m=sec2, t is the reaction time in sec, g is the acceleration due

to gravity and f is the coefficient of friction. The coefficient of friction f is given below for

various design speed.



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Table: Coefficient of longitudinal friction

When there is an ascending gradient of say +n%, the component of gravity adds to braking

action and hence braking distance is decreased. The component of gravity acting parallel to

the surface which adds to the braking force is equal to W sin α = W tanα = Wn=100.

Equating kinetic energy and work done:

Similarly the braking distance can be derived for a descending gradient. Therefore the general

equation is given by Equation 13.2.

Overtaking sight distance

The overtaking sight distance is the minimum distance open to the vision of the driver

of a vehicle intending to overtake the slow vehicle ahead safely against the traffic in the

opposite direction. The overtaking sight distance or passing sight distance is measured along

the center line of the road over which a driver with his eye level 1.2m above the road surface

can see the top of an object 1.2 m above the road surface. The factors that affect the OSD are:

x Velocities of the overtaking vehicle, overtaken vehicle and of the vehicle coming in the

opposite direction.

x Spacing between vehicles, which in-turn depends on the speed

x d1 the distance traveled by overtaking vehicle A during the reaction time t = t1 - t0

x d2 the distance traveled by the vehicle during the actual overtaking operation T = t3 - t1



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x d3 is the distance traveled by on-coming vehicle C during the overtaking operation (T).

Therefore:

OSD = d1 + d2 + d3

It is assumed that the vehicle A is forced to reduce its speed to vb, the speed of the slow

moving vehicle Band travels behind it during the reaction time t of the driver. So d1 is given

by:

d1 = vbt

Then the vehicle A starts to accelerate, shifts the lane, overtake and shift back to the original

lane. The vehicle A maintains the spacing s before and after overtaking. The spacing s in m is

given by:

s = 0:7vb + 6

Let T be the duration of actual overtaking. The distance traveled by B during the overtaking

operation is2s+vbT. Also, during this time, vehicle A accelerated from initial velocity vb and

overtaking is completed while reaching final velocity v. Hence the distance traveled is given

by:

The distance traveled by the vehicle C moving at design speed v m=sec during overtaking

operation is given

by:

The overtaking sight distance is (Figure)

Where vb is the velocity of the slow moving vehicle in m=sec2, t the reaction time of the

driver in sec, s is the spacing between the two vehicle in m given by equation 13.3 and a is



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the overtaking vehicles acceleration in m=sec2. In case the speed of the overtaken vehicle is

not given, it can be assumed that it moves 16 kmph slower the design speed. The acceleration

values of the fast vehicle depends on its speed and given in Table

Table 13:2: Maximum overtaking acceleration at different speeds

Overtaking zones

Overtaking zones are provided when OSD cannot be provided throughout the length

of the highway. These are zones dedicated for overtaking operation, marked with wide roads.

The desirable length of overtaking zones is 5 time OSD and the minimum is three times OSD

(Figure 13:2).

Sight distance at intersections



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At intersections where two or more roads meet, visibility should be provided for the

drivers approaching the intersection from either sides. They should be able to perceive a

hazard and stop the vehicle if required.:

o Enabling approaching vehicle to change the speed

o Enabling approaching vehicle to stop

o Enabling stopped vehicle to cross a main road

Horizontal curve

The presence of horizontal curve imparts centrifugal force which is a reactive force acting

outward on a vehicle negotiating it. Centrifugal force depends on speed and radius of the

horizontal curve and is counteracted to a certain extent by transverse friction between the tyre

and pavement surface. On a curved road, this force tends to cause the vehicle to overrun or to

slide outward from the centre of road curvature. The centrifugal force P in kg=m2 is given by

P = Wv2

gR

where W is the weight of the vehicle in kg, v is the speed of the vehicle in m=sec, g is the

acceleration due to gravity in m=sec2 and R is the radius of the curve in m. The centrifugal

ratio or the impact factor

W

P

is given by:

P = v2

W gR

The centrifugal force has two effects: a tendency to overturn the vehicle about the outer

wheels and a tendency for transverse skidding. Taking moments of the forces with respect to

the other when the vehicle is just about to override is give as:

Ph = W b

2

At the equilibrium over turning is possible when

V2 = b

gR 2h



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And for safety the following condition must satisfy:

b > V2 2h gR

The second tendency of the vehicle is for transverse skidding. i.e. When the centrifugal force

P is greater than the maximum possible transverse skid resistance due to friction between the

pavement surface and tire. The transverse skid resistance (F) is given by:

F = FA + FB

= f(RA + RB)

= fW

where FA and FB is the fractional force at tire A and B, RA and RB is the reaction at tire A

and B, f is the lateral coefficient of friction and W is the weight of the vehicle. This is

counteracted by the centrifugal force (P), and equating:

P = fW or

P = i

At equilibrium, when skidding takes place (from equation14.2)

P = f = v2

W gR

and for safety the following condition must satisfy:

f > v2

gR



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If this equation is violated, the vehicle will overturn at the horizontal curve and if equation

14.4 is violated, the vehicle will skid at the horizontal curve

Analysis of super-elevation

Super-elevation or cant or banking is the transverse slope provided at horizontal curve

to counteract the centrifugal force, by raising the outer edge of the pavement with respect to

the inner edge, throughout the length of the horizontal curve.

Forces acting on a vehicle on horizontal curve of radius R m at a speed of v m=sec2

are:

x P the centrifugal force acting horizontally out-wards through the center of gravity,

x W the weight of the vehicle acting down-wards through the center of gravity, and

x F the friction force between the wheels and the pavement, along the surface inward.

At equilibrium, by resolving the forces parallel to the surface of the pavement we get,



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At equilibrium, by resolving the forces parallel to the surface of the pavement we get,

P cosθ = W sin θ + FA + FB

= W sin θ + f (RA + RB)

= W sin θ + f (W cos θ + P sin θ)

where W is the weight of the vehicle, P is the centrifugal force, f is the coefficient of friction,

f is the transverse slope due to super elevation. Dividing by W cos θ, we get:

Attainment of super-elevation

Elimination of the crown of the cambered section by:

x Rotating the outer edge about the crown: The outer half of the cross slope is rotated

about the crown at a desired rate such that this surface falls on the same plane as the

inner half.

Rotation of the pavement cross section to attain full super elevation

There are two methods of attaining super elevation by rotating the pavement

x Rotation about the center line : The pavement is rotated such that the inner edge is

depressed and the outer edge is raised both by half the total amount of super

elevation, i.e., by E=2 with respect to the centre

x Rotation about the inner edge: Here the pavement is rotated raising the outer edge as

well as the centre such that the outer edge is raised by the full amount of

superelevation with respect to the inner edge.



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Mechanical widening

The reasons for the mechanical widening are: When a vehicle negotiates a horizontal

curve, the rear wheels follow a path of shorter radius than the front wheels as shown in

figure. this phenomenon is called off tracking, and has the effect of increasing the effective

width of a road space required by the vehicle. Therefore, to provide the same clearance

between vehicles travelling in opposite direction on curved roads as is provided on straight

sections, there must be extra width of carriageway available.. The expression for extra width

can be derived from the simple geometry of a vehicle at a horizontal curve as shown in figure

Let R1 is the radius of the outer track line of the rear wheel, R2 is the radius of the outer track

line of the front wheel l is the distance between the front and rear wheel, n is the number of

lanes, then the mechanical widening Wm (is derive below:



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If the road has n lanes, the extra widening should be provided on each lane. Therefore, the

extra widening of a road with n lanes is given

by,

Psychological widening

Widening of pavements has to be done for some psychological reasons also. There is

a tendency for the drivers to drive close to the edges of the pavement on curves. Some extra

space is to be provided for more clearance for the crossing and overtaking operations on

curves. IRC proposed an empirical relation for the psychological widening at horizontal

curves Wps:

Horizontal Transition Curves

Transition curve is provided to change the horizontal alignment from straight to circular

curve gradually and has a radius which decreases from infinity at the straight end (tangent

point) to the desired radius of the circular curve at the other end (curve point) There are five

objectives for providing transition curve and are given below:

1. To introduce gradually the centrifugal force between the tangent point and the beginning of

the circular curve, avoiding sudden jerk on the vehicle. This increases the comfort of

passengers.

2. To enable the driver turn the steering gradually for his own comfort and security,



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Type of transition curve

Different types of transition curves are spiral or clothoid, cubic parabola, and Lemniscates.

IRC recommends spiral as the transition curve because:

1. It full fills the requirement of an ideal transition curve, that is;

(a) rate of change or centrifugal acceleration is consistent (smooth) and

(b) Radius of the transition curve is 1 at the straight edge and changes to R at the curve point

(Ls / 1R) and calculation and field implementation is very easy.

Length of transition curve

The length of the transition curve should be determined as the maximum of the following

three criteria: rate of change of centrifugal acceleration, rate of change of super elevation, and

an empirical formula given by IRC.

1. Rate of change of centrifugal acceleration

At the tangent point, radius is infinity and hence centrifugal acceleration is zero. At the

end of the transition, the radius R has minimum value R. If c is the rate of change of

centrifugal acceleration, it can be written as:

The length of the transition curve Ls1 in m is

Ls1 = V3

cR

where c is the rate of change of centrifugal acceleration given by an empirical formula

suggested by IRC as

c = 80

75 + 3.6v

Cmin = 0:5; Cmax = 0:8:

2. Rate of introduction of super-elevation



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Raise (E) of the outer edge with respect to inner edge is given by E = eB = e(W +We). The

rate of change of this raise from 0 to E is achieved gradually with a gradient of 1 in N over

the length of the transition curve (typical range of N is 60-150). Therefore, the length of the

transition curve Ls2 is:

Ls2 = Ne (W +We)

3. By empirical formula

IRC suggest the length of the transition curve is minimum for a plain and rolling terrain:

Ls3 = 35v2

R

Steep and hilly terrain is: Ls3 =12.96v2

R

And the shift s as: s = L2s

24R

The length of the transition curve Ls is the maximum of equations

Ls = Max: (Ls1; Ls2 ;Ls3 )



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Setback Distance

Setback distance m or the clearance distance is the distance required from the

centerline of a horizontal curve to an obstruction on the inner side of the curve to provide

adequate sight distance at a horizontal curve. The set back distance depends on:

1. Sight distance (OSD, ISD and OSD),

2. Radius of the curve, and

3. Length of the curve.

Case (a) Ls < Lc

For single lane roads:



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Case (b) Ls > Lc

For single lane:



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Curve Resistance

When the vehicle negotiates a horizontal curve, the direction of rotation of the front and the r

ear wheels are different. The front wheels are turned to move the vehicle along the curve,

whereas the rear wheels seldom turn. This is illustrated in figure 16:4.The rear wheels exert a

tractive force T in the PQ direction. The tractive force available on the front wheels is Tcosθ

in the PS direction as shown in the figure 16:4. This is less than the actual tractive force, T

applied. Hence, the loss of tractive force for a vehicle to negotiate a horizontal curve is:

CR = T -- T cosα



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Vertical alignment

The vertical alignment of a road consists of gradients(straight lines in a vertical plane)

and vertical curves. The vertical alignment is usually drawn as a profile, which is a graph

with elevation as vertical axis and the horizontal distance along the centre line of the road as

the the horizontal axis.

Gradient

Gradient is the rate of rise or fall along the length of the road with respect to the horizontal.

While aligning a highway, the gradient is decided designing the vertical curve. Before

finalising the gradients, the construction cost, vehicular operation cost and the practical

problems in the site also has to be considered.

Types of gradient

Many studies have shown that gradient upto seven percent can have considerable

effect on the speeds of the passenger cars. On the contrary, the speeds of the heavy vehicles

are considerably reduced when long gradients a sat as two percent is adopted. Although, atter

gradients are desirable, it is evident that the cost of construction will also be very high.

Ruling gradient

The ruling gradient or the design gradient is the maximum gradient with which the

designer attempts to design the vertical profile of the road. This depends on the terrain, length

of the grade, speed, pulling power of the vehicle and the presence of the horizontal curve. In

atter terrain, it may be possible to provide at gradients, but in hilly terrain it is not economical

and sometimes not possible also.



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Minimum gradient

This is important only at locations where surface drainage is important. Camber will

take care of the lateral drainage. But the longitudinal drainage along the side drains requires

some slope for smooth flow of water.

Limiting gradient

This gradient is adopted when the ruling gradient results in enormous increase in cost

of construction. On rolling terrain and hilly terrain it may be frequently necessary to adopt

limiting gradient.

Exceptional gradient

Exceptional gradient are very steeper gradients given at unavoidable situations. They

should be limited for short stretches not exceeding about 100 meters at a stretch.

Summit curve

Summit curves are vertical curves with gradient upwards. They are formed when two

gradients meet as illustrated in figure below in any of the following four ways:

1. When a positive gradient meets another positive gradient

2. When positive gradient meets a at gradient

3. When an ascending gradient meets a descending gradient.

4. When a descending gradient meets another descending gradient



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Type of Summit Curve

Many curve forms can be used with satisfactory results; the common practice has

been to use parabolic curves in summit curves. This is primarily because of the ease with it

can be laid out as well as allowing a comfortable transition from one gradient to another.

Length of the summit curve

The important design aspect of the summit curve is the determination of the length of

the curve which is parabolic. As noted earlier, the length of the curve is guided by the sight

distance consideration.

Distance .Let L is the length

Case a: Length of summit curve greater than sight distance

The situation when the sight distance is less than the length of the curve



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Case b: Length of summit curve less than sight distance

When stopping sight distance is considered the height of driver's eye above the road surface

(h1) is taken as 1.2 meters, and height of object above the pavement surface (h2) is taken as

0.15 meters. If overtaking sight distance is considered, then the value of driver's eye height

(h1) and the height of the obstruction (h2) are taken equal as 1.2 meters.

Valley curve

Valley curve or sag curves are vertical curves with convexity downwards. They are

formed when two gradients meet as illustrated in figure below in any of the following four

ways:

1. When a descending gradient meets another descending gradient

2. When a descending gradient meets a at gradient

3. When a descending gradient meets an ascending gradient



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4. When an ascending gradient meets another ascending gradient

Length of the valley curve

The valley curve is made fully transitional by providing two similar transition curves of equal

length The transitional curve is set out by a cubic parabola y = bx3

where b = 2N3/

L2 The

length of the valley transition curve is designed based on two criteria:

1. Comfort criteria; that is allowable rate of change of centrifugal acceleration is limited to a

comfortable level of about 0:6m=sec3.

2. Safety criteria; that is the driver should have adequate headlight sight distance at any part

of the country.

Comfort criteria

The length of the valley curve based on the rate of change of centrifugal acceleration

that will ensure comfort: Let c is the rate of change of acceleration, R the minimum radius of

the curve, v is the design speed and t is the time, then c is given as:

Ls = V3



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cR

For a cubic parabola, the value of R for length Ls is given by:

Safety criteria

R = Ls

N

Length of the valley curve for headlight distance may be determined for two conditions:

x length of the valley curve greater than stopping sight distance and

x Length of the valley curve less than the stopping sight distance.

Case 1: Length of valley curve greater than stopping sight distance (L > S)

The total length of valley curve L is greater than the stopping sight distance SSD. The

sight distance available will be minimum when the vehicle is in the lowest point in the valley.

This is because the beginning of the curve will have infinite radius and the bottom of the

curve will have minimum radius which is a property of the transition curve.

Where L is the total length of valley curve, N is the deviation angle in radians or tangent of

the deviation angle or the algebraic difference in grades, and c is the allowable rate of change

of centrifugal acceleration which may be taken as 0:6m/sec3.



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Where N is the deviation angle in radians, h1 is the height of headlight beam, α is the head

beam inclination in degrees and S is the sight distance. The inclination α is = 1 degree.

Case 2 Length of valley curve less than stopping sight distance (L < S)

The length of the curve L is less than SSD. In this case the minimum sight distance is

from the beginning of the curve. The important points are the beginning of the curve and the

bottom most part of the curve. If the vehicle is at the bottom of the curve, then its headlight

beam will reach far beyond the endpoint of the curve whereas, if the vehicle is at the

beginning of the curve, then the headlight beam will hit just outside the curve. Therefore, the

length of the curve is derived by assuming the vehicle at the beginning of the curve. The case

is shown in figure below.



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The gradients are very small and are acceptable for all practical purposes. We will not be able

to know prior to which case to be adopted. Therefore both has to be calculated and the one

which satisfies the condition is adopted.

UNIT 5 PAVEMENT MATERIALS

Introduction

Subgrade soil

Subgrade soil is an integral part of the road pavement structure which directly

receives the traffic load from the pavement layers. The subgrade soil and its properties are

important in the design of pavement structure. The main function of the subgrade is to give

adequate support to the pavement and for this the subgrade should possess sufficient stability

under adverse climate and loading conditions.

The formation of waves, corrugations, rutting and shoving in black top pavements and

the phenomena of pumping, blowing and consequent cracking of cement concrete pavements

are generally attributed due to the poor subgrade conditions.



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Desirable Properties

The desirable properties of soil as a highway material are

x Stability

x Incompressibility

x Permanency of strength

x Minimum changes in volume and stability under adverse conditions of weather and

ground water

x Good drainage, and

x Ease of compaction.

The soil should possess adequate stability or resistance to permanent deformation under

loads, and should possess resistance to weathering, thus retaining the desired subgrade

support. Minimum variation in volume will ensure minimum variation in differential

Soil classification

1. Grain size analysis

According to size of grains soil is classified as gravel, sand, silt and clay. As per

Indian standard classification the limits of grain size are as follows.

Gravel Sand Silt Clay

C

0.6

M

0.2

F C

0.02

M

0.006

F C

0.006

M

0.002

F

Fraction of soils

2.0mm 0.06mm 0.002mm

Larger than 2.00mm size

Between 2.00mm – 0.06 mm size

Between 0.06mm – 0.002 mm size

Smaller than 0.002 size

Gravel

Sand

Silt

Clay

2. Highway Research Board (HRB) classification of soils



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This is also called American Association of State Highway Officials (AASHO)

classification of Revised Public Roads Administration (PRA) soil classification system. Soils

are divided into seven groups A-I to A-7. A-I, A-2 and A-3 soils are granular soils,

percentage fines passing 0.074 mm sieve being less than 35. A-4, A-5, A-6 and A-7, soils are

fine grained or silt-clay soils, passing 0.074 mm sieve being greater than 35 percent.

A-1 soils are well graded mixture of stone fragments, gravel coarse sand, fine sand

and non-plastic or slightly plastic soil binder. The soils of this group are subdivided into two

subgroups, A- 1-a, consisting predominantly of stone fragments or gravel and A-I-b

consisting predominantly of coarse sand.

A-2 group of soils include a wide range of granular soils ranging from A- 1 to A-3

groups, consisting of granular soils and upto 35% fines of A-4, A-5, A-6 or A-7 groups.

Based on the fines content, the soils of A-2 groups are subdivided into subgroups A-2-4, A-2-

5, A-2-6 and A-2-7.

A-3 soils consist mainly, uniformly graded medium or fine sand similar to beach sand

or desert blown sand. Stream-deposited mixtures of poorly graded fine sand with some coarse

sand and gravel are also included in this group.

A-4 soils are generally silty soils, non-plastic or moderately plastic in nature with

liquid limit and plasticity index values less than 40 and 10 respectively

A-5 soils are also silty soils with plasticity index less than 10%, but with liquid limit

values exceeding 40%. These include highly elastic or compressible, soils, usually of

diatomaceous of micaceous character.

A-6 group of soils are plastic clays, having high values of plasticity index exceeding

10% and low values of liquid limit below 40%; they have high volume change properties

with variation in moisture content.

A-7 soils are also clayey soils as A-6 soils, but with high values of both liquid limit

and plasticity index, (LL greater than 40% and P1 greater than 10%). These soils have low

permeability and high volume change properties with changes in moisture content.



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California Bearing Ratio (CBR) Test

This is a penetration test developed by the California division of highway. For

evaluating the stability of soil subgrade and other pavement materials. The test results have

been correlated with flexible pavement thickness requirement for highway and airfield. CBR

test may be conducted in the laboratory on a prepared specimen in a mould or in situ in the

field.

Laboratory CBR test

The laboratory CBR apparatus consists of

x Cylindrical mould

Mould 150mm dia, 175mm height with 50mm collar height, detachable perforated base with

spacer disc of 148mm dia and 47.7mm thick is used to obtain a specimen of exactly

127.3mm height.

x Loading Machine

Compression machine operated at a constant rate of 1.25mm/min.Loading frame with

cylindrical plunger 50mm dia & dial gauge for measuring the deformation due to application

of load.

x Compaction rammer

Type of compaction No of layers Wt of hammer

(kg) Fall (cm) No of blows

Light compaction 3 2.6 31 56 Heavy compaction 5 4.89 45 56

x Annular weight or surcharge weight

2.5 Kgs of surcharge wt of 147mm dia are placed on specimen both at the soaking and

testing of prepared samples.

Procedure



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x CBR test may be performed on undisturbed soil specimens.

x About 5kgs of soil is taken passing though 20mm IS sieve and retained on 4.75mm IS

sieve

x The soil is mixed with water upto OMC.

x The spacer disc is placed at the bottom of the mould over the base plate & a coarse filter

paper is placed over the spacer disc.

x Then the moist soil sample is to be compacted over this in the mould by adopting either

IS light compaction or IS heavy compaction.

x For IS heavy compaction 3 equal layers of compacted thickness about

56 evenly distributed blows from 2.6kgs rammer.

44mm by applying

x For IS heavy compaction 5 equal layers of compacted thickness about 26.5mm by

applying 56 evenly distributed blows from 4.89 kg rammer.

x After compacting the last layer, The collar is removed and the excess soil above the top of

the mould is evenly trimmed off by means of straight edge (of 5mm thickness).

x Clamps are removed ant the mould with compacted soil is lifted leaving below the

perforated base plate & the spacer disc which is removed.

x Then the mould with compacted soil is weighed

x Filter paper is placed on the perforated base plate &* the mould with compacted soil is

inverted & placed in position over the base plate.

x Now the clamps of the base is tightened

x Another filter paper is placed on the placed on the top surface of the sample & the

perforated plate with adjustable stem is placed over it.

x Now surcharge weights of 2.5 or 5kgs are placed over the perforated plate & the whole

mould with the weights is placed in a water tank for soaking such that water can enter the

specimen both from the top & bottom.

x The initial dial gauge readings is recorded & the test set up is kept undisturbed in the

water tank to allow soaking of the soil specimen for full 4 days or 96 hrs.

x The final dial gauge reading is noted to measure the expansion & swelling of the

specimen due to soaking.



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x The swell measurement assembly is removed, the mould is taken out of the water tank &

the sample is allowed to drain in a perpendicular position for 15 min surcharge wt,

perforated plate with stem, filter paper are removed.

x The mould with the soil subgrade is removed from the base plate & is weighed again to

determine the wt of water absorbed.

x Then the specimen is clamped over base plate surcharge wt‟s are placed on specimens

centrally such that the penetration test could be conducted.

x The mould with base plate is placed under the penetration plunger of loading machine.

x The penetration plunger is seated +at the centre of the specimen & is brought in contact

with the top surface of the soil sample by applying a seating load of 4kgs.

x The dial gauge for measuring the penetration values of the plunger is fitted in position

x The dial gauge of proving ring & the penetration dial gauge are set to 0.

x The load is applied though the penetration plunger at a uniform rate of 1.5mm/min

x The load reading are recorded at penetration reading 0, 0.5, 1.0, 1.5, 2, 2.5, 3, 4, 5, 7.5, 10

& 12.5mm.

x In case the load reading starts decreasing before 12.5mm penetration, the max load & the

corresponding penetration values are recorded.

x After the final reading the load is released & the mould from loading machine.

x The proving ring calibration factor is noted so that load dial gauge value can be converted

into the load in kg.

Calculation

Swelling or expansion ratio is calculated from the formula.

Expansion ratio = (100 ( df – di))/h

Where,

df = Final dial gauge after soaking in mm

di = Initial dial gauge before soaking in mm

h = initial ht of the specimen in mm



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Therefore, CBR= Load sustained by the specimen at 2.5 or 5mm penetration x

100

Load sustained by std specimen at corresponding penetration level

CBR at 2.5mm = P1 (kg) x 100%

1370

CBR at 5mm = P2 (kg) x 100%

1370

x Generally CBR value @ 2.5mm penetration is higher & this value is adopted.

x The initial upward concavity of the load penetration is due to the piston surface not

being fully in contact with top of the specimen.

x Top layer of soaked soil being too soft.

Modulus of subgrade reaction of soil

Plate bearing test

x The plate bearing test has been devised to evaluate the supporting power of subgrade or

any other pavement layer by using plates of larger diameter.

x Plate bearing test was originally meant to find the modulus of subgrade reaction in the

westergards‟s analysis for wheel load stresses in cement concrete pavement.

x In the plate bearing test a compressive stress is applied to the soil or pavement layer

through rigid plates of relatively large size & the deflection are measurement for various

stress values.

x The deflection level is generally limited to a low value of 1.25mm to 5mm.

Modulus subgrade reaction (k)

x K may be defined as the pressure sustained per unit deformation of subgrade at specified

pressure level using specified plate size.

x The standard palte size for finding K value is 75cm dia in same test a smaller plate of

30cm dia is also used (75,60,45,30 & 22.5 cm dia).



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Apparatus used

Bearing plate:

Mild steel of 75cm dia & 1.5 to 2.5 cm thickness.

Loading equipment:

Reaction frame or dead load applied may be measured either by a proving ring or dial gauge

assembly.

Settle measurement:

It may be made by means of 3 or 4 dial gauge fixed on the periphery of the bearing plate from

an independent datum frame. Datum frame should be supported from the loaded area.

Procedure

x At the test site, about 20cm top soil is removed & the site is leveled & the plate is

properly seated on the prepared surface.

x The stiffening plates of decreasing dia are placed & the jack & proving ring assembly are

fitted to provide reaction against the frame.

x 3 or 4 dial gauges are fixed on the periphery of the palte from the independent datum

frame foe measuring settlement.

x A seating load of 0.07 kg/cm2 (320kgs for 75 dia) is applied & released after a few sec.

x The settlement dial gauges reading are now noted corresponding to zero load.

x A load is applied by means of jack sufficient to cause an average settlement of about

0.25mm.

x When there is no perception increase in settlement or when the rate of settlement is less

than 0.025mm/min (case of clayey soil or wet soil), the reading of the settlement dial

gauge are noted & the avg settlement is found & the load is noted from the proving ring

dial reading.

x The load is then increased till settlement increases to a further amount of about 0.25mm

& the avg settlement & load are found.



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x The procedure is repeated till the settlement reaches 0.175cm.

x A graph is plotted with mean settlement versus mean bearing pressure (load/unitarea) as

shown in fig.

Bearing pressure settlement curve.

x The pressure p (kg/cm2) corresponding to a settlement delta = 0.125cm (obtaines from

the graph shown above)

x The modulus of subgrade reaction k is calculated from the relation.

K = P kg/cm2

0.125

Correction for smaller plate size

x In some cases the load capacity may not be adequate to cause 75cm dia plate to settle

0.175cm.

x In such a case a plate of smaller dia (say 30cm) may be used.

x Then K value should be found by applying a suitable correction for plate size.

x Assuming the subgrade to be an elastic medium with modulus of elasticity E (kg/cm2),

the theoretical relationship of deformation (cm) under a rigid plate of radius a (cm) is

given by

Delta = 1.18Pa

E

But, K = P

D

Substitute the value of D in K

Therefore K = P x E

1.18 Pa K = E

1.18a

x If the value of E is taken as constant for a soil, Then k x a = constant

x i.e. Ka = ka or K = ka



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a

x Hence if the test is carried out with a smaller plate of radius a & the modulus of subgrade

reaction K is found.

x Then the corrected value of modulus of subgrade reaction K for std plate of radius a, is

given by K = k1 a1

A

AGGREGATES

Introduction

Aggregates form the major portion of pavement structure and they form the prime

materials used in pavement construction. Aggregates have to bear stresses occurring due to

the wheel loads on the pavement and on the surface course they also have to resist wear due

to abrasive action of traffic.

Strength

The aggregates to be used in road construction should be sufficiently strong to

withstand the stresses due to traffic wheel load. The aggregates which are to be used in top

layers of the pavements, particularly in the wearing course have to be capable of

with4jnhighs1cssesinaddItion to

strength resistance to crushing.

- wear and tear; hence they should possess sufficient

Toughness

Aggregates in the pavements are also subjected to impact due to moving wheel loads.

Sever impact like hammering is quite move on water bound macadam roads where stones

protrude out especially after the monsoons.

Durability



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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 may called soundness.

Shape of Aggregates

The size of the aggregates is first qualified by the size of square sieve opening

through which an aggregate may pass, and not by the shape. Aggregates which happen to fall

in a particular size range may have rounded, cubical, angular flaky or elongated shape of

particles. It is e and donated particles will have less strength and durability when compared

with cubical angular or rounded articles of the same Stone. Hence too flaky and too much

elongated aggregates should be avoided as far as possible.

Adhesion with Bitumen

The aggregates used in bituminous pavements should have less affinity with water

when compared with bituminous materials, otherwise the bituminous coating on the

aggregate will be stripped off in presence of water.

Tests for Road Aggregate

In order to decide the suitability of the road stones for use in construction, the

following tests are carried out:

(a) Crushing test

(b) Abrasion test

(c) Impact test

(d) Soundness

(e) Shape test

(f) Specific gravity and water absorption test



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(g) Bitumen adhesion test

The essential features of these tests are discussed below. Separate tests are available

for testing cylindrical stone specimens and coarse aggregates for crushing, abrasion and

impact tests. But due to the difficulties of preparing cylindrical stone specimen which need

costly core drilling, cutting and polishing equipment, the use of such tests are now limited.

Testing of aggregates is easy and simulate the field condition better, as such these are

generally preferred.

BITUMINOUS MATERIALS

Introduction

Bituminous binders used in pavement construction works include both bitumen and

tar. Bitumen is a petroleum product obtained by the distillation of petroleum crude where-as

road tar is obtained by the destructive distillation of coal or wood. Both bitumen and tar have

similar appearance, black in colour though they have different characteristics. Both these

materials can be used for pavement works.

(i)

(ii)

paving bitumen from Assam petroleum, denoted as A-type and designated as grades

A35, A 90, etc.

paving bitumen from other sources denoted as S-type and designated as grades S 35,

S 90, etc.

Types of Bituminous Materials

Bituminous material used in highway construction may be broadly divided as

(i)

(ii)

Bitumen and

Tar

Bitumen may be further divided as petroleum asphalt or bitumen and native

asphalt.There are different forms in which native asphalts are available. Native asphalts are

those which occur in a pure or nearly pure state in nature. Native asphalts which are

associated with a large proportion of mineral matter are called rock asphalts. The viscosity of

bitumen is reduced some times by a volatile diluent; this material is called cutback.



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Bitumen

Crude petroleum obtained from different places are quite different in their

composition. The portion of bituminous material present in the petroleum‟s may widely differ

depending on the source. Almost all the crude petroleum‟s contain considerable amounts of

water along with crude oil. Hence the petroleum should be dehydrated first before carrying

out the distillation. General types of distillation processes are fractional distillation and

Tests on Bitumen

Bitumen is available in a variety of types and grades. To judge the suitability of these

binders various physical tests have been specified by agencies like ASTM, Asphalt Institute,

British Standards Institution and the ISI. These tests include penetration test, ductility tests,

softening point test and viscosity test. For classifying bitumen and studying the performance

of bituminous pavements, the penetration and ductility tests are essential.

The various tests on bituminous materials are

(a) Penetration tests (b) Ductility tests (c) Viscosity tests

(d) Float test (e) Specific gravity test (f) Softening point test

(g) Flash and Fire point test (h) Solubility test (i) Spot test

(j) Loss on heating test (k) Water content test

Cutback Bitumen

Cutback bitumen is defined as the bitumen, the viscosity of which has been reduced

by a colatile diluent. For use in surface dressings, some type of bitumen macadam and

soilbitumen it is necessary to have a fluid binder which can be mixed relatively at low

temperatures. Hence to increase fluidity of the bituminous binder at low temperatures the

binder is blended with a volatile solvent. After the cutback mix in construction work, the

volatile gets evaporated and the cutback develops the properties. The viscosity of the cutback

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bitumen and volatile oil used as the diluent. Cutback bitumens are available in three types,

namely,

(i) Rapid Curing (RC)

(ii) Medium Curing (MC) and

(iii) Slow Curing (SC)

This classification is based on the rate of curing or hardening after the application. The grade

of cutback or its fluidity is designed by a figure which follows the initials; as an example RC-

2 means that it is a rapid curing cutback of grade 2.The cutback with the lowest viscosity is

designated by numeral 0, such as RC-0 and SC-0. Suffix numerals 0, 1, 2, 3, 4 and 5

designate progressively thicker or more viscous cutbacks as the numbers increase. This

number indicates a definite viscosity irrespective of the type of cutback; in other words, RC-

2, MC-2 all have the same initial viscosity at a specified temperature. The initial viscosity

values (in seconds, standard tar viscometer) of various grades of cutbacks as per ISI

specifications are given in Table 6.7.

Thus lower grade cutbacks like RC-0, RC-l etc. would contain high prop solvent

when compared with higher grades like RC-4 or RC-5, RC-0 and MC-0 may contain

approximately 45 percent solvent and 55 percent bitumen, whereas, RC-5 and MC-5 may

contain approximately 15 percent solvent and 85 percent bitumen.

Rapid Curing Cutbacks are bitumens, fluxed or cutback with a petroleum Distillate such as

nephta or gasoline which will rapidly evaporate after using in construction, leaving the

bitumen binder. The grade of the R.C. cutback is governed by the proportion of the solvent

used. The penetration value of residue from distillation up to 3600C of RC cutback bitumen

is 80 to 120.

Medium curing cutbacks are bitumen fluxed to greater fluidity by blending with a

intermediate-boiling-point solvent like kerosene or light diesel oil. MC cutbacks evaporate

relatively at slow rate because the kerosene-range solvents will not evaporate rapidly as the

gasoline-range solvents used in the manufacture of RC cutbacks. Hence the designation



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„medium curing‟ is given to this cutback type. MC products have good wetting properties and

so satisfactory coating of fine grain aggregate and sandy soils is possible.

Slow curing cutbacks are obtained either by blending bitumen with high-boiling-point

gas oil, or by controlling the rate of flow and temperature of the crude during the first cycle

of refining. SC cutbacks or wood soils harden or set way slowly as it is a semi volatile

material.

Various tests carried out on cut-backs bitumen are

(a)

(b)

Viscosity tests at specified temperature using specified size of orifice.

Distillation test to find distillation fractions, up to specified temperature and to find

the residue from distillation up to 360°C

(c) Penetration test, ductility test and test for matter soluble in carbon disulphide on

(d)

residue from distillation up to 360°C

Flash point test on cutback using Pensky Martens closed type apparatus.

Bituminous Emulsion

A bitumen emulsion is liquid product in which a substantial amount of bitumen is

suspended in a finely divided condition in an aqueous medium and stabilized by means of

one or more suitable materials. An emulsion is a two phase system consisting of two

immiscible liquids; the one being dispersed as fine globules in the other.Usually, bitumen or

refined tar is broken up into fine globules and kept in suspension in water. A small proportion

of an emulsifier is used to facilitate the formation of dispersion and to keep the globules of

dispersed binder in suspension.

Some of the general properties of road emulsions are judged by the following tests

(i) Residue on Sieving: It is desirable to see that not more than 0.25 percent by w of

emulsion consists of particles greater than 0.15 mm diameter.



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(ii) Stability to Mixing with Coarse Graded Aggregate: This test carried out to fit the

emulsion breaks down and coats the aggregate with bitumen too early before mixing

is complete.

(iii) Stability to Mixing with Cement : This test is carried out to assess the stability

emulsions when the aggregate contains large proportions of fines.

(iv) Water Cement: To know the percentage water in the emulsion which depend the type

of the emulsion.

(v) Sedimentation: Some sedimentation may occur when a drum of emulsion is standing

before use, but on agitation, the emulsion redisperses and can be used.

(vi) Viscosity: The viscosity of emulsified bitumen should be low enough to be sprayed

through jets or to coat the aggregates in simple mixing.

Three types of bituminous emulsion are prepared, viz., (i) Rapid Setting (RS),

Medium Setting (MS) and (iii) Slow Setting (SS) types. Rapid Setting type emulsion is

suitable for surface dressing and penetration macadam type of construction. Medium Setting

type is used for premixing with coarse aggregates and Slow Setting type emulsion is suitable

for fine aggregate mixes.

Tar:

Tar is the viscous liquid obtained when natural organic materials such as wood and

coal carbonized or destructively distilled in the absence of air. Based on the material from

which tar is derived, it is referred to as wood tar or coal tar; the latter is more widely used for

road work because it is superior. Three stages for the production of road tar are

(i) Carbonization of coal to produce crude tar

(ii) Refining or distillation of crude tar and

(iii) Blending of distillation residue with distillate oil fraction to give the desired road tar.



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There are five grades of roads tars, viz., RT- I, RT-2, RT-3, RT-4 and RT-5, based on

their viscosity and other properties. RT-l has the lowest viscosity and is used for surface

painting under exceptionally cold weather as this has very low viscosity. RT-2 is

recommended for standard surface painting under normal Indian climatic conditions. RT-3

may be used for surface painting, renewal coats and premixing chips for top course and light

carpets. RT-4 is generally used for premixing tar macadam in base course. For grouting

purposes RT-5 may be adopted, which has the highest viscosity among the road tars.

The various tests that are carried out on road tars are listed below

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

(viii)

(ix)

(x)

(xi)

Specific gravity test

Viscosity test on standard tar viscometer

Equiviscous temperature (EVT)

Softening point

Softening point of residue

Float test

Water content

Distillation fraction on distillation upto 200°C, 200°C to 270°C and 270°C to

3 30°C.

Phenols, percent by volume

Naphthalefle, percent by weight

Matter insoluble in toluene, percent by weight

The requirements for the five grades of road tars based on the above test results are given by

the ISI. Bitumen and tar have black to dark brown colour. But bitumen is a petroleum product

whereas tar is produced by the destructive distillation of coal or wood.

Comparison between tar & bitumen

Bitumen Tar

It has black to dark brown color It also has black to dark brown in color



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It is natural petroleum product Tar is produced by the destructive distillation

of coal or wool

It is soluble in carbon disulphide & in carbon

tetrachloride

Tar is soluble only in toluene

It has better weather resisting property It has inferior weather resisting property

Bitumen are less temp susceptible Tar is more temp susceptible

Free carbon content is less Free carbon content is More

It neither binds the aggregate well nor retains

the presence of water

It binds aggregate more easily & retain it

better in the presence of water.

BITUMINOUS PAVING MIXES

Requirements of Bituminous Mixes

The mix design should aim at an economical blend, with proper gradation of

aggregates and adequate proportion of bitumen so as to fulfil the desired properties of the

mix. Bituminous concrete or asphaltic concrete is one of the highest and costliest types of

flexible pavement layers used in the surfacing course. The desirable properties of a good

bituminous mix are stability, durability, flexibility, skid resistance and workability.

.

Mix design methods should aim at determining the properties of aggregates and

material which would give a mix having the following properties.

bituminous

(i) Sufficient stability to satisfy the service requirements of the pavement and the traffic

conditions, without undue displacements.



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(ii) Sufficient bitumen to ensure a durable pavement by coating the aggregate bonding

them together and also by water-proofing the mix.

(iii) Sufficient voids in the compacted mix as to provide a reservoir space amount of

additional

stability.

compaction due to traffic and to avoid flushing, bleeding and loss of

(iv) Sufficient flexibility even in the coldest season to prevent cracking due to repeated

application of traffic loads.

(v) Sufficient workability while placing and compacting the Mix.

(vi) The mix should be the most economical one that would produce a stable, durable and

skid resistant pavement.

Three mix design methods, namely, Marshall, Hveem and Hubbard-Field methods are

briefly explained in the following paragraphs. These methods have been widely used by

various agencies in the design and construction with satisfactory results. In each of these

methods, the laboratory test results on the mixes have been correlated with the performance

studies in developing the design criteria.



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Unit 6 Introduction to pavement design

A highway pavement is a structure consisting of superimposed layers of processed

materials above the natural soil sub-grade, whose primary function is to distribute the applied

vehicle loads to the sub-grade. The pavement structure should be able to provide a surface of

acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics,

and low noise pollution.

Requirements of a pavement

The pavement should meet the following requirements:

x Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-

grade soil

x Structurally strong to withstand all types of stresses imposed upon it

x Adequate coefficient of friction to prevent skidding of vehicles

x Smooth surface to provide comfort to road users even at high speed

Types of pavements

The pavements can be classified based on the structural performance into two,

flexible pavements and rigid pavements. In flexible pavements, wheel loads are transferred

by grain-to-grain contact of the aggregate through the granular structure. The flexible

pavement, having less flexural strength, acts like a flexible sheet (e.g. bituminous road). On

the contrary, in rigid pavements, wheel loads are transferred to sub-grade soil by flexural

strength of the pavement and the pavement acts like a rigid plate (e.g. cement concrete roads).

Flexible pavements

Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-

grain transfer through the points of contact in the granular structure (see Figure 19:1). The



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wheel load acting on the pavement will be distributed to a wider area, and the stress decreases

with the depth. Taking advantage of this stress distribution characteristic

The lower layers will experience lesser magnitude of stress and less quality material can be

used. Flexible pavements are constructed using bituminous materials. These can be either in

the form of surface treatments (such as bituminous surface treatments generally found on low

volume roads) or, asphalt concrete surface courses (generally used on high volume roads such

as national highways).

pavement layer

.

Types of Flexible Pavements

The following types of construction have been used in flexible pavement:

x Conventional layered flexible pavement,

x Full - depth asphalt pavement, and

x Contained rock asphalt mat (CRAM).

Conventional flexible pavements are layered systems with high quality expensive materials

are placed in the top where stresses are high, and low quality cheap materials are placed in

lower layers.

Full - depth asphalt pavements are constructed by placing bituminous layers directly on the

soil subgrade. This is more suitable when there is high traffic and local materials are not

available.



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Contained rock asphalt mats are constructed by placing dense/open graded aggregate layers

in between two asphalt layers. Modified dense graded asphalt concrete is placed above the

sub-grade will significantly reduce the vertical compressive strain on soil sub-grade and

protect from surface water

Rigid pavements

Rigid pavements have sufficient flexural strength to transmit the wheel load stresses

to a wider area below. A typical cross section of the rigid pavement is shown in Figure below

Compared to flexible pavement, rigid pavements are placed either directly on the prepared

sub-grade or on a single layer of granular or stabilized material.

Since there is only one layer of material between the concrete and the sub-grade, this

layer can be called as base or sub-base course. In rigid pavement, load is distributed by the

slab action, and the pavement behaves like an elastic plate resting on a viscous medium Rigid

pavements are constructed by Portland cement concrete (PCC) and should be analyzed by

plate theory instead of layer theory,

Types of Rigid Pavements

Rigid pavements can be classified into four types:

x Jointed plain concrete pavement (JPCP),

x Jointed reinforced concrete pavement (JRCP),



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x Continuous reinforced concrete pavement (CRCP), and

x Pre-stressed concrete pavement (PCP).

Jointed Plain Concrete Pavement is plain cement concrete pavements constructed with

closely spaced contraction joints. Dowel bars or aggregate interlocks are normally used for

load transfer across joints. They normally has a joint spacing of 5 to 10m.

Jointed Reinforced Concrete Pavement Although reinforcements do not improve the

structural capacity significantly, they can drastically increase the joint spacing to 10 to 30m.

Dowel bars are required for load transfer. Reinforcements help to keep the slab together even

after cracks.Continuous Reinforced Concrete Pavement Complete elimination of joints are

achieved by reinforcement.

Factors affecting pavement design

Traffic and loading

Traffic is the most important factor in the pavement design. The key factors include

contact pressure, wheel load, axle configuration, moving loads, load, and load repetitions.

Contact pressure

The tire pressure is an important factor, as it determines the contact area and the

contact pressure between the wheel and the pavement surface. Even though the shape of the

contact area is elliptical, for sake of simplicity in analysis, a circular area is often considered.

Wheel load

The next important factor is the wheel load which determines the depth of the

pavement required to ensure that the subgrade soil is not failed. Wheel configuration affects

the stress distribution and deflection within a pavement. Many commercial vehicles have dual

rear wheels which ensure that the contact pressure is within the limits. The normal practice is

to convert dual wheel into an equivalent single wheel load so that the analysis is made

simpler.



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Axle configuration

The load carrying capacity of the commercial vehicle is further enhanced by the

introduction of multiple axles.

Moving loads

The damage to the pavement is much higher if the vehicle is moving at creep speed.

Many studies show that when the speed is increased from 2 km/hr to 24 km/hr, the stresses

and deflection reduced by 40 per cent.

Repetition of Loads

The influence of traffic on pavement not only depends on the magnitude of the wheel

load, but also on the frequency of the load applications. Each load application causes some

deformation and the total deformation is the summation of all these

Environmental factors

Environmental factors affect the performance of the pavement materials and cause

various damages. Environmental factors that affect pavement are of two types, temperature

and precipitation.

Equivalent single wheel load

To carry maximum load within the specified limit and to carry greater load, dual

wheel, or dual tandem assembly is often used. Equivalent single wheel load (ESWL) is the

single wheel load having the same contact pressure, which produces same value of maximum

stress, deflection, tensile stress or contact pressure at the desired depth. The procedure of

finding the ESWL for equal stress criteria is provided below. This is a semi-rational method,

known as Boyd and Foster method, based on the following assumptions:

x equalancy concept is based on equal stress;

x contact area is circular;

x influence angle is 45o; and



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x soil medium is elastic, homogeneous, and isotropic half space.

Where P is the wheel load, S is the center to center distance between the two wheels, d is the

clear distance between two wheels, and z is the desired depth.

Equivalent single axle load

Vehicles can have many axles which will distribute the load into different axles, and

in turn to the pavement through the wheels. A standard truck has two axles, front axle with

two wheels and rear axle with four wheels. But to carry large loads multiple axles are

provided. Since the design of flexible pavements is by layered theory, only the wheels on one

side needed to be considered. On the other hand, the design of rigid pavement is by plate

theory and hence the wheel load on both sides of axle need to be considered. Legal axle load:

Repetition of axle loads:

The deformation of pavement due to a single application of axle load may be small

but due to repeated application of load there would be accumulation of unrecovered or

permanent deformation which results in failure of pavement.

Equivalent axle load factor:

An equivalent axle load factor (EALF) defines the damage per pass to a pavement by

the ith type of axle relative to the damage per pass of a standard axle load. While _finding the

EALF, the failure criterion is important. Two types of failure criteria‟s are commonly

adopted: fatigue cracking and rutting. The fatigue cracking model has the following form:

Where, Nf is the number of load repetition for a certain percentage of cracking, _t is the

tensile strain at the

bottom of the binder course, E is the modulus of elasticity, and f1; f2; f3 are

constants. If we consider fatigue



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cracking as failure criteria, and a typical value of 4 for f2, then:

Where, i indicate Ith

vehicle, and std indicate the standard axle. Now if we assume that the

strain is proportional to the wheel load,

Similar results can be obtained if rutting model is used, which is:

where Nd is the permissible design rut depth (say 20mm), s the compressive strain at the top

of the subgrade,

and f4; f5 are constants. Once we have the EALF, then we can get the ESAL as given below.

Equivalent single axle load, ESAL =

Where, m is the number of axle load groups, Fi is the EALF for ith

axle load group, and ni is

the number of passes of ith axle load group during the design period.

Example Let number of load repetition expected by 80 KN standard axle is 1000, 160 KN is

100 and 40 KN is 10000. Find the equivalent axle load. Solution:



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IRC method of design of flexible pavements

Design traffic

The method considers traffic in terms of the cumulative number of standard axles

(8160 kg) to be carried by the pavement during the design life. This requires the following

information:

1. Initial traffic in terms of CVPD

2. Traffic growth rate during the design life

3. Design life in number of years

4. Vehicle damage factor (VDF)

5. Distribution of commercial traffic over the carriage way.

Initial traffic

Initial traffic is determined in terms of commercial vehicles per day (CVPD). For the

structural design of the pavement only commercial vehicles are considered assuming laden

weight of three tones or more and their axle loading will be considered. Estimate of the initial

daily average traffic flow for any road should normally be based on 7-day 24-hour classified

traffic counts (ADT). In case of new roads, traffic estimates can be made on the basis of

potential land use and traffic on existing routes in the area.



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Traffic growth rate

Traffic growth rates can be estimated

(i) by studying the past trends of traffic growth, and

(ii) By establishing econometric models. If adequate data is not available, it is

recommended that an average annual growth rate of 7.5 percent may be adopted.

Design life

For the purpose of the pavement design, the design life is defined in terms of the

cumulative number of standard axles that can be carried before strengthening of the pavement

is necessary. It is recommended that pavements for arterial roads like NH, SH should be

designed for a life of 15 years, EH and urban roads for 20 years and

other categories of roads for 10 to 15 years.

Vehicle Damage Factor

The vehicle damage factor (VDF) is a multiplier for converting the number of

commercial vehicles of different axle loads and axle configurations to the number of standard

axle-load repetitions. It is defined as equivalent number of standard axles per commercial

vehicle. The VDF varies with the axle configuration, axle loading, terrain, type of road, and

from region to region. The axle load equivalency factors are used to convert different axle

load repetitions into equivalent standard axle load repetitions. For these equivalency factors

refer IRC: 37 2001. The exact VDF values are arrived after extensive field surveys.

Vehicle distribution

A realistic assessment of distribution of commercial traffic by direction and by lane is

necessary as it directly affects the total equivalent standard axle load application used in the

design. Until reliable data is available, the following distribution may be assumed.

x Single lane roads: Traffic tends to be more channelized on single roads than two lane

roads and to allow for this concentration of wheel load repetitions, the design should

be based on total number of commercial vehicles in both directions.



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x Two-lane single carriageway roads: The design should be based on 75 % of the

commercial vehicles in both directions.

x Four-lane single carriageway roads: The design should be based on 40 % of the

total number of commercial vehicles in both directions.

x Dual carriageway roads: For the design of dual two-lane carriageway roads should

be based on 75 % of the number of commercial vehicles in each direction. For dual

three-lane carriageway and dual four-lane carriageway the distribution factor will be

60 % and 45 % respectively.

Numerical example

Design the pavement for construction of a new bypass with the following data:

1. Two lane carriage way

2. Initial traffic in the year of completion of construction = 400 CVPD (sum of both

directions)

3. Traffic growth rate = 7.5 %

4. Design life = 15 years

5. Vehicle damage factor based on axle load survey = 2.5 standard axle per commercial

vehicle

6. Design CBR of subgrade soil = 4%.



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Rigid pavement design

Wheel load stresses - Westergaard's stress equation

The cement concrete slab is assumed to be homogeneous and to have uniform elastic

properties with vertical sub-grade reaction being proportional to the deflection. Westergaard

developed relationships for the stress at

interior, edge and corner regions, denoted as _i; _e; _c in kg/cm2 respectively and given by

the equation.

where h is the slab thickness in cm, P is the wheel load in kg, a is the radius of the wheel load

distribution in cm, l the radius of the relative stiffness in cm 29.1 and b is the radius of the

resisting section in cm



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Temperature stresses

Temperature stresses are developed in cement concrete pavement due to variation in

slab temperature. This is caused by (i) daily variation resulting in a temperature gradient

across the thickness of the slab and (ii) seasonal variation resulting in overall change in the

slab temperature. The former results in warping stresses and the later in frictional stresses.

Warping stress

The warping stress at the interior, edge and corner regions, denoted as ά ti; ά te; ά tc in

kg/cm2 respectively and given by the equation

Frictional stresses

The frictional stress ά f in kg/cm2 is given by the equation.



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Where W is the unit weight of concrete in kg/cm2 (2400), f is the coefficient of sub grade

friction (1.5) and L is the length of the slab in meters.

Combination of stresses

The cumulative effect of the different stress give rise to the following thee critical cases

x Summer, mid-day: The critical stress is for edge region given by α critical = α e + α te

– αf

x Winter, mid-day: The critical combination of stress is for the edge region given by α

critical = α e+ α te + α f

x Mid-nights: The critical combination of stress is for the corner region given by α

critical = α c + α tc



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UNIT 7 HIGHWAY CONSTRUCTION

Introduction

The science of highway engineering raises some fundamental questions as to what is a

road or highway, how is it planned and designed and lastly how is it built. By now in the

preceding chapters, Depending upon the desired strength of the pavement, the aggregate

gradations and the type and proportion of binders are decided. These three basic binder

medium give rise to a number of construction methods.

Types of Highway Construction

The highway types are classified as below:

(i)

(ii)

(iii)

(iv)

(v)

Earth road and gravel roads

Soil stabilized roads

Water bound macadam (WBM) road

Bituminous or black-top roads

Cement concrete roads

The roads in India are classified based on location and functions. All the roads do not cater

for the same amount of traffic volume or intensity. Since the funds available at hand for

financing the construction projects are also meager, it is necessary to have roads which cost

less. The adoption of low cost roads is now preferred in developing countries like India where

large lengths of roads are to be constructed in the rural areas with the limited finances

available in the country. Earth roads and stabilized roads are typical examples of low cost

roads. Stabilised soil roads are gaining importance in the form of low cost roads. .



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EARTHWORK

General

The subgrade soil is prepared by bringing is to the desired grade and camber and by

campacting adequately. The subgrade may be either in embankment or in excavation,

depending on the topography and the finalized vertical alignment of the road to be

constructed.

Excavation

Excavation is the process of cutting or loosening and removing earth including rock form its

original position. Transporting and dumping it as a fill or spoil bank. The excavation or

cutting mat be needed in soil, soft rock or even in hard rock, before preparing the subgrade.

Embankment

When it is required to raise the grade line of a highway above the existing ground

level it becomes necessary to construct embankments. The grade line may be raised due to

any of the following reasons

i)

ii)

To keep the subgrade above the high ground water table.

To prevent damage to pavement due to surface water and capillary water.

iii) To maintain the design standards of the highway with respect to the Verticalalignment.

The design elements in highway embankments are:

i)

ii)

iii)

iv)

v)

Height

Fill material

Settlement

Stability of foundation, and

Stability of slopes



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Height

The height of the embankment depends on the desired grade line of the highway and the soil

profile or topography. Also the height of the fill is some times governed by stability of

foundation, particularly when the foundation soil is weak.

Fill Material

Granular soil is generally preferred as highway embankment material. Silts, and clays

are considered less desirable. Organic soils, particularly peat are unsuitable. The best of the

soils available locally is often selected with a view to keep the lead and lift as low as

possible. At times light-weight fill material like cinder may be used to reduce the weight

when foundation soil is weak.

Settlement

The embankment may settle after the completion of construction either due to

consolidation and settlement of the foundation or due to settlement of the fill or due to both.

If the embankment foundation consists of compressible soil with high moisture content, the

consolidation can occur due to increase in the load. The settlement of the fill is generally due

to inadequate compaction during construction and hence by proper compaction this type of

settlement may be almost eliminated. Whatever be the type of settlement, it is desirable that

the settlement is almost complete before the construction of pavement.

Stability of Foundation

When the embankment foundation consists of weak soil just beneath or at a certain

depth below in the form of a weak stratum, it is essential to consider the stability of the

foundation against a failure. This is all the more essential in the case of high embankments.

The foundation stability is evaluated and the factor of safety is estimated by any of the

following approaches:

(a) Assuming a certain failure surface such as a circular arc or any otier composite shape

and analysing it with Swedish circular arc analysis or method of wedges, as the case

may be.



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(b) Estimating the average shear stress and strength at the foundation layers by

approximate methods and estimating the factor of safety.

(c) using theoretical analysis based on elastic theory.

The factor of safety in the case of compressible soil foundation is likely to be

minimum just after the completion of the embankment. Later due to consolidation of

foundation and consequent gain in strength there will be an increase in the foundation factor

of safety.

Stability of Slopes

The embankment slopes should be stable enough to eliminate the possibility of a

failure under adverse moisture and other conditions. Hence the stability of the slope should

be checked or the slope should be designed providing minimum factor of safety of 1.5. Often

much flatter slopes are preferred in highway embankments due to aesthetic and other reasons.

Construction of embankments

The embankment may be constructed either by rolling in relatively thin layers or by

hydraulic fills. The former is called rolled-earth method and is preferred in highway

embankments. Each layer is compacted by rolling to a satisfactory degree or to a desired

density before the next layer is placed.

Preparation of Subgrade

The preparation of subgrade includes all operations before the pavement structure

could be laid over it and compacted. Thus the preparation of subgrade would include site

clearance, grading (embankment or cut section) and compaction. The subgrade may be

situated on embankment or excavation or at the existing ground surface. In all the cases, site

should be cleared off and the top soil consisting of grass roots rubbish and other organic

matter are to be removed. Next, the grading operation is started so as to bring the vertical

profile of the subgrade to designed grade and camber. Bull dozers, scrapers and blade graders

are useful equipment to speed up this work. It is most essential to compact the top of

subgrade, upto a depth of about adequately before placing the pavement layer.



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Soil Compaction

By compaction of soil, the particles are mechanically constrained to be packed more

closely, by expelling part of the air voids. Compaction increases the density and stability,

reduces settlement and lowers the adverse effects of moisture. Hence proper compaction of

fills, subgrade, sub-base and base course are considered essential for proper highway

construction.

The various factors influencing soil compaction include the moisture content, amount and

type of compaction, soil type and stone content. It is a well known fact that there is an

optimum moisture content (OMC) for a soil which would give maximum dry density for a

particular type and amount of compaction. Hence it is always desirable to compact the soil at

the OMC after deciding the compacting equipment.

Compacting equipment

Soil compaction is achieved in the field either by rolling, ramming or by vibration.

Hence the compacting equipment may also be classified as rollers, rammers and vibrators.

Compactions of sands are also achieved by watering ponding and jetting.

Rollers

The principle of rollers is the application of pressure, which is slowly increased and

then decreased. The various type of rollers which are used for compaction are smooth wheel,

pneumatic tyred and sheep foot rollers. Further the construction equipment such as trucks,

tractors and bull dozers also help in compaction of the materials to some extent.

CONSTRUCTION OF EARTH ROADS

General

An earth road is the cheapest type of road prepared from natural soil. The pavement

sections is totally made out of the soil available at site and at near-by borrow pits. The type of

construction by and large, depends upon the type of soil at site. The camber provided to the

earth roads is very steep and ranges between I in 20 to I in 33. The steep cross Slope helps to



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keep the pavement surface free of standing water; otherwise the soil being Previous, the

water would damage the pavement section by softening it. The maximum cross slope of 1 in

20 is recommended to avoid erosion due to rain waters and formation of cross ruts.

Specification of Materials

Soil of the following properties is considered satisfactory for constructing earth roads:

Base Course Wearing course

Clay content < 5% 10 to 18%

Silt content 9 to 32% 5 to 15%

Sand Content 60 to 80% 60 to 80%

Liquid limit <35% <35%

Plasticity index <6% 40 to 10%

Construction Procedure

The construction of earth road may be divided into the following steps:

x Material. The soil survey is carried out and suitable borrow pits are located within

economical haulage distances. The borrow pits are usually selected outside the land

width. The trees, shrubs, grass roots and other organic matter including top soil a

removed before excavating earth for construction.

x Location. The centre line and road edges are marked on the ground along the alignment,

by driving wooden pegs. Reference pegs are also driven to help in following the desired

vertical profile of the road during construction. The spacing of the reference pegs

depends on the estimated length of road construction per day

x Preparation of subgrade. The various operations involved in the preparation of subgrade

are as follows:

a) Clearing site

b) Excavating and construction of fills to bring the road to a desired grade.



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c) Shaping of subgrade.

The site clearance may be carried out manually using appliances like spade, pick and

shovel. Mechanical equipment like dozer, scraper and ripper may also be used for the

purpose. Construction of fills and excavation of costs to bring the road profile to the

desired grade may also be done either manually or using excavation, hauling and

compaction equipment.

x Pavement construction. The borrowed soil (more than one soil type mixed to the

desired proportion, if necessary) is dumped on the prepared subgrad and pulverized.

The field moisture content is checked and additional water is added, if necessary, to

bring it upto OMC. light compaction is considered desirable. The camber of the

finished pavement surface is checked and corrected if necessary.

x Opening to traffic. The compacted earth road is allowed to dry out for a few days

before opening to traffic.

CONSTRUCTION OF GRAVEL ROADS

General

Gravel roads are considered superior to earth roads as they can carry heavier traffic.

The road consists of a carriageway constructed using the gravels. The camber mat be between

I in 25 and 1 in 30. A well compacted crushed rock or gravel road is fairly resilient and does

not become slippery when wet.

Material

Hard variety of crushed stone or gravel of specified gradation is uses. However

Varieties of Stone may also be utilized. There are no specifications for the mal Rounded

stones and river gravel are not preferable as there is poor interlocking.


x Material Gravel to be used for the construction is stacked along the

proposed road.

sides of the



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x Preparation of subgrade. Site is cleared and fills and cuts are completed. Trench is

formed to the desired depth of construction. The width of the trench is made equal to

that of the carriageway. The trench is brought to the desired grade and is compacted.

x Pavement construction. Crushed gravel aggregates are placed carefully in the trench

so as to avoid segregations. Aggregates are spread with greater thickness at centre and

less towards the edges so as to obtain the desired camber. The layer is rolled using

smooth wheeled rollers starting from the edges and proceeding towards the centre

with an overlap of atleast half the width of roller in the longitudinal direction. Some

quantity of water may also be sprayed and rolling is done again s that the compaction

is effective. The camber is checked and corrected from time to time using a template

or camber board.

x Opening to traffic. A few days after the final rolling and drying out, the road is

opened to the traffic.

CONSTRUCTION OF WATER BOUND MACADAM ROADS

General

The Water bound macadam (WBM) is the construction known after the name of John

also article 2.16 and 2.17. The term macadam in the present day means, the pavement base

course made of crushed or broken aggregate mechanically interlocked by rolling and the

voids filled with screening and binding material with the assistance of water.

Specifications of Materials for WBM Pavement

Coarse Aggregates

The coarse aggregate used in WBM generally consists of hard varieties of crushed

aggregates or broken stones. However, soft aggregates like over burnt bricks metal or

naturally occurring soft aggregates such as kankar or laterite may be used. Crushed slag

obtained from blast furnace may also be used.



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Property Requirements for Pavement layer

Sub-base Base Course Surfacing course

(i) Los Angeles abrasion

(maximum value, percent)

or

60 50 40

(ii) Aggregate impact


50 40 30

(iii) Flakiness index


- 15 15

Properties of Coarse Aggregates

The crushed stone aggregate should be generally hard, durable and free from flaky

and elongated particles. The IRC specifies the following ph requirement of coarse aggregates

for WBM construction, in terms of the test value the three pavement layers.

Size and Grading Requirements of Coarse Aggregates

The coarse aggregates for each layer of construction should, as far as possible

conform to any one of the three gradings specified below. Grading No.1. consists of Coarse

aggregates of size range 90 to 40 mm and is more suitable for sub-base course. Thickness of

compacted layer is usually 100 mm. Grading No. 2 consists of aggregates size range 63 to 40

mm and grading No. 3 of range 50 to 20 mm and compacted thickness of each layer is

normally 75 mm..

Binding Material



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Binding material consisting of fine grained material is used in WBM construction to

prevent raveling of the stones Kankar nodules or lime stone dust may also be utilized, if

locally available. The binding material with plasticity index value 4 to 9% is used in WBM

surface course construction; the plasticity index of binding course material should be less

than 6.0% in the case of WBM layers used as base course or sub-base course, with

bituminous surfacing. If the screenings used consist of crushable material like moorum or soft

gravel, there is no need to apply binding material, unless the plasticity index value is low.

Quantity of Materials

x The approximate loose quantities of materials required in m3 for 10 cm compacted

thickness of WBM sub-base using coarse aggregate of grading no I per 10 m2 area

are:

(a) Coarse aggregate size 90 to 40 mm = 1.21 to 1.43

(b)

(c)

Stone screening type A, 12.5 mm size

or

Crushable type screenings (moorum/gravel)

Binding material for sub-base course

= 0.40 to 0.44

= 0.44 to 0.47

= 0.88 to 0.10

x The approximate loose quantities of materials required in m3 for 7.5 cm compacted

thickness of WBM base course or surfacing course using coarse aggregate of grading

No. 2 per 10 m2 area are:

(a)

(b)

(c)

Coarse aggregate size 63 to 40mm

Stone screening type A, 12.5 mm size for base course

Stone screenings for surfacing course

Alternatively, Stone screenings type B,

9.0 mm size for base course

9.0 mm size for surfacing

Alternatively, crushable type screenings

Binding material for base course

Binding material for surfacing course

= 0.91 to 1.07

= 0.18 to 0.21

= 0.15 to 0.17

= 0.30 to 0.33

= 0.24 to 0.26

= 0.33 to 0.35

= 0.06 to 0.09

= 0.10 to 0.15

(Note: Binding material is not required if crushable type of screening is used).



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Preparation of Foundation for Receiving the WBM course

The foundation for receiving the new layer of WBM may be either the subgrade or

sub-base or base course. This foundation layer is prepared to the required grade and camber

and the dust and either loose materials are cleaned. On existing road surface, the depressions

and pot-holes are filled and the corrugations are removed by scarifying and reshaping the

surface to the required grade and camber as necessary. If the existing surface is a bituminous

surfacing, ftirrows of depth 50 mm and width 50 mm cut at 1.0 m intervals and at 45 degrees

to the centre line of the carriageway before laying the Coarse aggregate.

Provision of Lateral confinement

Lateral confinement is to be provided before starting WBM construction. This may be

done by constructing the shoulders to advance, to a thickness equal to that of the compacted

WBM layer and by trimming the inner sides vertically

Spreading of Coarse Aggregates

The coarse aggregates are spread uniformly to proper profile to even thickness upon

the prepared foundation and checked by templates. The WBM course is normally constructed

to compacted thickness of 7.5 cm except in the case of WBM sub-base course using coarse

aggregate grading no.1 which is of 10.0 cm compacted thickness.

Rolling

After spreading the coarse aggregates properly, compaction is done by a three

wheeled power roller of capacity 6 to 10 tons or alternatively by an equivalent vibratory

roI1q the weight of the roller depends on the type of coarse aggregates.

Application of Screenings.

After the coarse aggregates are rolled adequately, the dry screenings are gradually

over the surface to fill the interstices in three or more applications. Dry rolling is continued as

the screenings are being spread and brooming carried out.



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Sprinkling and Grouting

After the application of screenings, the surface is sprinkled with water, swept rolled.

Wet screenings are swept into the voids using hand brooms. Ad• screenings are applied and

rolled till the coarse aggregates are well bonded and firmly set.

Application of Binding Material

After the application of screening and rolling, binding material is applied at a uniform

and slow rate at two or more successive thin layers. After each application of binding

material, the surface is copiously sprinkled with water and wet slurry swept with brooms to

fill the voids.

Setting and Drying

After final compaction, the WBM course is allowed to set over-night. On the next day

the „hungry‟ spots are located and are filled with screenings or binding material, lightly

sprinkled with water if necessary and rolled. No traffic is allowed till the WBM layer sets and

dries out.

Checking of Surface Evenness and Rectification of Defects

The surface evenness of longitudinal direction is checked by 3.0 m straight edge and

the number of undulations exceeding 12mm in the case if WBM layer of grading no. 1 and

10mm in the case of grading nos. 2 and 3 are recorded in each completed length of 300m; the

maximum number of undulations permitted in each case in 30. The spots with 15mm

undulations are marked for rectification of defects.

CONSTRUCTION OF BITUMINOUS PAVEMENTS

Introduction

Bituminous pavements are in common use in India and abroad. It is Possible to

construct relatively thin bituminous pavement layers over an existing Pavement. Therefore,

these are commonly adopted as wearing course. Flexible pavement could be strengthened in



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stages by constructing bituminous pavement layers one after another in a certain period of

time unlike the cement concrete pavement construction

Types of Bituminous Construction

Number of types and methods are in use for bituminous pavement construction. It is

attempted to broadly classify them here based on the methods of construction. The following

construction techniques are in use:

x Interface treatment like prime coat and tack coat

x Surface dressing and seal coat

x Grounted or penetration type constructions :

a) Penetration macadam

b) Built-up spray Grout.

x Premix which may be any of the following:

a) Bituminous bound macadam

b) Carpet

c) Bituminous concrete

d) Sheet asphalt or rolled asphalt

e) Mastic asphalt

Explanatory Notes on Bituminous Construction Types

x Interface Treatment

Thus surface of the existing pavement layer is to be cleaned to remove dust and dir

and a thin layer of bituminous binder is to be sprayed 1.

Prime coat: Bituminous prime coat is the first application of a low viscosity liquid

bituminous material over an existing porous or absorbent pavement surface like the WBM

base course.

Tack coat. Bituminous tack coat is the application of bituminous material over existing

pavement surface which is relatively impervious like an existing bituminous surface or a



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cement concrete pavement or a pervious surface like the WBM which has already been

treated by a prime coat.

x Bituminous Surface Dressing

Bituminous Surface Dressing (BSD) is provided over an existing pavement to serve as

thin wearing coat. The single coat surface dressing consists of a single application of

bituminous binder material followed by spreading of aggregate cover and rolling. When the

surface dressing is similarly done in two layers, it is called „two coat bituminous surface

dressing‟.

x Seal Coat

Seal coat is usually recommended as a top coat over certain bituminous pavements

which are not impervious, such as open graded bituminous constructions like premixed carpet

and grouted Macadam. Seal coat is also provided over an existing bituminous pavement

which is worn out.:

(a)

(b)

(c)

To seal the surfacing against the ingress of water

To develop skid resistant texture

To enliven an existing dry or weathered bituminous surface.

x Penetration Macadam

Bituminous Penetration Macadam or Grouted Macadam is used as a base or binder

course. The coarse aggregates are first spread and compacted well in dry state and after that

hot bituminous binder of relatively high viscosity is sprayed in fairly large quantity at the top.

x Built-up Spray Grout

Built-up Spray Grout (BSG) consists of two-layer composite construction of

compacted crushed aggregates with application of bitumin9us binder after each layer for

bonding and finished with key aggregates at the top to provide a total compacted thickness of

75 mm.



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x Premix Methods

In this group of methods the aggregates and the bituminous binder are mixed

thoroughly before spreading and compacting. It is possible to coat each particle of aggregate

with the binder still the quantity of binder used may be considerably lesser than penetration

macadam type construction. In premixed constructions, the quantity of bitumen used could be

precisely controlled and they offer increased stability of the mix even with lower bitumen

contents.

Bituminous Macadam

Bituminous Macadam (BM) or Bitumen Bound Macadam is a premixed construction

method consisting of one or more courses of compacted crushed aggregates premixed with

bituminous binder, laid immediately after mixing. The BM is laid in compact thicknesses of

75 mm or 50 mm and three different gradations of aggregates have been suggested for each

thickness to provide open graded and semi-dense constructions.

x Bituminous Premixed Carpet

Premixed Carpet (PC) consists of coarse aggregates of 12.5 and 10.0 mm sizes,

premixed with bitumen or tar binder are compacted to a thickness of 20 mm to serve as a

surface course of the pavement. Being a open graded construction, the PC is to be invariably

covered by a suitable seal coat such as premixed sand-bitumen seal coat before opening to

traffic. The PC consists of all aggregates passing 20 mm and retained on 6.3mm sieve. When

a fairly well graded material as per specification is used for the construction of the

bituminous carpet of thickness 20 o 25 mm, the construction method is called semi-dense

carpet.

x Bituminous Concrete or Asphalt Concrete

Bituminous Concrete or Asphaltic Concrete (AC) is a dense graded premixed

bituminous mix which is well compacted to form a high quality pavement surface Course.

The AC consists of a carefully proportioned mixture of coarse aggregates fine aggregates,

mineral filler and bitumen and the mix is designed by an appropriate method such as the



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Marshall method to fulfil the requirements of stability, density, flexibility and voids. The

thickness of bituminous concrete surface course layer usually ranges from 40 to 75 mm. The

IRC has provided specification for 40 mm thick AC surface course for highway pavements.

x Sheet Asphalt

Sheet asphalt or rolled asphalt is a dense sand-bitumen premix of compacted thickness

25 mm, used as a wearing course. The sheet asphalt consists of well graded coarse to fine

sand (without coarse aggregates) and a suitable penetration grade bitumen to from a dense

and impervious layer. This is usually laid over cement concrete pavement to provide an

excellent riding surface. The sheet asphalt also protects the joints in cement concrete

pavements and could cause a reduction in warping stresses due to a decrease in the

temperature variations between top and bottom of the concrete slab.

x Mastic Asphalt

Mastic asphalt is a mixture of bitumen, fine aggregates and filler in suitable

proportions which yields a voidless and impermeable mass. Though the ingredients in mastic

asphalt are similar to those in bituminous concrete, properties of mastic asphalts are quite

different. The mastic asphalts when cooled results in a hard, stable and durable layer suitable

to withstand heavy traffic. This material also can absorb vibrations and has property f self-

healing of cracks without bleeding. It is a suitable surfacing materials for bridge deck slabs.

Construction Procedure for Bituminous Macadam

The Bituminous Macadam (BM) bitumen bound macadam is a premix laid

immediately after mixing and then compacted. It is an open graded construction suitable only

as a base or binder course. When this layer is exposed as a surface course, at least a seal coat

is necessary.

Specifications of Materials:



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The grades of bitumen used are 30/40, 60/70 and 80/100 penetration. Road tar RT-4,

cutback and emulsion can also be used in cold mix construction technique. The binder

content used varies from 3.0 to 4.5 percent by weight of the mix). Aggregates used are of low

porosity fulfilling the following requirements for the base Course.

Los Angle abrasion value 50 percent max.

Aggregate impact value 35 percent max.

Flakiness index 15 percent max.

Stripping at 40°C after 24 hours immersion (CRRI test) 25 percent max.

Loss with sodium sulphate, 5 cycles 12 percent max.

For binder course the specified maximum abrasion and impact values are 40 and 30

percent respectively.

The grading of the aggregates for 75 mm and 50 mm thickness for base and binder

course instruction as specified by Indian Roads Congress are given in Table 8.4 (a) &

respectively. The quantity of aggregates required for 10 m2 of bitumen bound macadam are

0.60 to 0.75 m3 and 0.90 to 1.0 m3 respectively, for 50 and 75 mm compacted thickness. The

bitumen quantity would be determined based on the grading adopted as specified above.

Constructions Steps

x Preparation of existing layer: The existing layer is prepared to a proper profile. Pot holes

are patched and irregularities are made even. The surface is properly cleaned.

x Tack coat or prime coat application: A track coat is applied of thin layer of bitumen

binder on the existing layer either using the sprayer or a pouring can. the quantity of

application is 40 to 7.5 kg per 10 m2 for black top layer and 7.5 to 10kg per 10 m2 for

untreated WBM layer.

x Premix preparation: The bitumen binder and aggregates as per recommended gradings

are separately heated to the specified temperatures and are then placed in the mixer

chosen for the job. The mixing temperature for each grading and the bitumen binder is



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also specified based on. the laboratory results. A tolerance of ± 10°C is allowed. The

mixing is done till a homogeneous mixture is obtained. The mixture is then carried to the

site for its placement through a transporter or a wheel barrow.

x Placement. The bituminous paving mixture is then immediately placed on the desired

location and is spread with rakes to a pre-determined thickness. The camber profile is

checked with a template. It may be stated here that a compacting temperature also

influences the strength characteristic of the resulting pavement structure. It is therefore

required that the minimum time is spent between the placement of the mix and the rolling

operations.

x Rolling and finishing The paving mix. The rolling is done with 8 to 10 tones tandem

roller. The rolling is commenced from the edges of the pavement construction towards the

centre, and uniform overlapping is provided. The finished surface should not show

separate lines of markings due to defective or improper rolling. The roller wheels are kept

damp, otherwise the paving mix may partly stick to the wheels and the finishing may not

be good. A variation of 6 mm over 3 m length is allowed in the cross profile. The number

of undulations exceeding 10 nun should be less than 30 in 300 m length of pavement.

Construction Procedure for Bituminous Concrete

The bituminous concrete is the highest quality of construction in the group of black

top surface. Being of high cost specifications, the bituminous mixes are properly designed to

satisfy the design requirements of the stability and durabi1ity. The mixture contains dense

grading of coarse aggregate, fine aggregate and mineral filler coated with bitumen binder.

The mix is prepared in a hot-mix plant. The thickness of the bituminous concrete layer

depends upon the traffic and quality of base course.

The specifications of materials and the construction steps for bituminous concrete or asphaltic

concrete (AC) surface course are given below:

Specification of Materials:

a) Binder: Bitumen of grade 3 0/40,60/70 or 80/100 may be chosen depending Upon tic

condition of the locality.



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b) Aggregates and Filler: The coarse aggregates should fulfill the following requirements

:

Aggregate impact value, maximum percent : 30

or Loss Angeles abrasion value, max percent : 40

Flakiness index, max percent : 25

Stripping at 40°C after 24 hours, max percent : 25

Soundness:

Loss with sodium sulphate in 5 cycles, max. percent : 12

Loss with magnesium sulphate in 5 cycles, max. percent : 18

The gradation of aggregates and filler should conform to those given in Table 8.5.

Table 8.5 Gradation of Aggregates for Bituminous Concrete

Sieve Size, mm Percent passing by

weight

Grading 1 Grading 2

20.00 - 100

12.50 100 80-100

10.00 80-100 70-90

4.75 55-75 50-70

2.36 35-50 35-50

0.60 18-29 18-29

0.30 13-23 13-23

0.15 8-16 8-16

0.75 4-10 4-10



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CONSTRUCTION OF CEMENT CONCRETE PAVEMENTS

Introduction

The Cement concrete pavement maintains a very high recognition among the engineer

and the road users alike. Due to the excellent riding surface and pleasing appearance, the

cement concrete roads are very much preferred.

Specifications of material for cement concrete pavement slabs.

The materials required for plain concrete slabs are cement coarse aggregates, fine

aggregates and water. In case reinforcement is provided, steel wire fabric or bar mats may be

used of the required size and spacing. Other materials are for the construction of joints, such

as load transfer devices, joints filler and sealer.

Cement:

Ordinary portland cement is generally used. In case of urgency rapid hardening

cement may also be used to reduce curing time.

Coarse aggregates:

The maximum size of coarse aggregates should not exceed one fourth the slab

thickness. The gradation of coarse aggregate may range from 50 to 4.75 mm or 40 to 4.75

mm, the aggregate is collected in two size ranges, one below and the other above 20mm size.

When the grading is from 20 to 50 mm, the materials are collected in two groups, below and

above 25 mm size.:

Aggregate crushing value

Aggregate impact value

Los Angles abrasion value

Soundness, average loss in

Weight after 10 cycles

: 30 % max.

: 30 % max.

: 30 % max. as per the ISI and

35% max. as per the IRC

: 12 percent max. in sodium sulphate

: 18 percent max. in magnesium sulphate



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Fine aggregate.

Natural sands should be preferred as fine aggregate though crushed Stones may also

be used.

Proportioning of concrete.

The concrete may be proportioned so as to obtain a minimum modulus of rupture of

40 kg/cm2 on field specimens after 28 days curing or to develop a minimum compressive

strength of 280 kg/cm2 at 28 days, or higher value as desired in the design.

Plants and Equipment

The equipment necessary for the construction of cement concrete slabs are for

batching, placing, finishing and carrying the concrete pavement. Equipment commonly used

are given below.

Concrete Mixer:

If batching by volume is required then the separate measuring boxes are provided for

the different aggregates. Each box is provided with a straight edge for striking off excess

material after filling.

Batching Device

Concrete mixer of adequate capacity of the batch type is provided. It has a rated

capacity of not less than 0.2 m3 of mixed concrete. The mixture is equipped with a water

measuring device capable of accurate measurement of water required per batch. Some

mixtures are also equipped with timing devices which automatically lock the discharge lever

during the full time of mixing and releases it at the end of mixing period.

Wheel Borrow

Wheel borrows with two wheels are used to transport concrete for short distances

from the mixer.



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Vibrating Screed

Vibrating screed comprises of a wooden or mild steel screed with suitable handles

driven by vibrating units mounted thereon, propelled either electrically or by compressed air

or by a petrol engine, and travelling on side forms.

Internal Vibrators

It comprises of vibrating head with suitable motive power either of compressed air,

electricity or of a petrol driven engine right enough to ensure proper control and

manipulation in the mass of concrete. It is used to ensure compaction of the cement concrete

along with the forms and also to avoid any tendency of honey-combing at the edges of the

slab.

Tools and appliances for surface, finishing operations in common use are float,

straight edge, belt and fiber brush.

Float

The longitudinal float is of 75 cm length and 7.5 cm width and is made of hard wood

and is fixed with handle. (See Fig. 8.15). This is used for smoothing the concrete.

Straight Edge:

It is used to check the finished pavement surface in longitudinal direction. It is made

of hard wood with M.S. plate at bottom, 3 meter in length, 10 cm in width with two handles

as shown in Fig. 8.16.

Belt:

Canvas belts are used for finishing the pavements surface before the concrete hardens.

The canvas is of 25 cm width and atleast 75 cm longer than the width of pavement slab. It has

two wooden handles at the end. See Fig. 8.17.



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Fibre Brush:

Fibre brush broom is used to make broom marks across the pavement surface and to

make it skid resistance. Hard fibres are used projecting out of the wooden bursh of length

45cm and width 7.5 cm, with a handle about 2 meter long.

Edging Tool

The edging tool is used for rounding the transverse edges at expansion joints and the

longitudinal edges. The vertical limb of this tool extends to the required depth. The rounded

edge of the M.S. plate has radius f 6 mm.

Other Small Tools

Other small tools d equipment such as spades, shovels and pans water pots etc.

necessary for the work are also provided.

Construction steps for cement concrete pavement slab

(i) Preparation of Subgrade and Sub-base

The subgrade or sub-base for laying of the concrete slabs should comply with the

wing requirement; that no soft spots are present in the subgrade or sub-base; that the

uniformly compacted subgrade or sub-base extends atleast 30 cm on either side of the width

to be concreted; that the subgrade is properly drained; that the minimum modulus subgrade

reaction obtained with a plate bearing test is 5.54 kg/cm2.

over the soil subgrade. In such a case, the moistening of the subgrade prior to placing

of the concrete is not required.

ii) Placing of Forms

The steel or wooden forms are used for the purpose.

The steel forms are of M.S. channel sections and their depth is equal to the thickness

the pavements. The sections have a length of at least 3 m except on curves of less than 45.0 m

radius, where shorter sections are used.



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(iii) Batching of Material and Mixing

After determining the proportion of ingredients for the field mix, the fine aggregates

and coarse aggregates are proportioned by weight in a weight-batching plant and placed into

the hopper along with the necessary quantity of cement. Cement is measured by the bag. All

batching of material is done on the basis of one or more whole bags of cement.

(iv) Transporting and Placing of Concrete

The cement concrete is mixed in quantities required for immediate use and is

deposited on the soil subgrade or sub-base to the required depth and width of the

pavement section within the form work in continuous operation.

(v) Compaction and Finishing

The surface of pavement is compacted either by means of a power-driven finishing

machine or by a vibrating hand screed. For areas where the width of the slab is very

small as at the corner of road junctions, etc., hand consolidation and finishing may be

adopted:

(a) Concrete as soon as placed, is struck off uniformly and screeded to the crown

and cross-section of the pavement to conform the grade.

(b) The tamper is placed on the side forms and is drawn ahead in combination

with a series of lifts and drops to compact the concrete.

Floating and Straight Edging

The concrete is further compacted by means of the longitudinal float. The longitudinal

float is held in a position parallel to carriageway centre line and passed gradually from one

side of the pavement to the other. After the longitudinal floating is done and the excess water

gets disappeared, the slab surface is tested for its grade and level with the straight edge.



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HIGHWAY DRAINAGE

INTRODUCTION

Highway drainage is the process of removing and controlling excess surface and sub-

soil water within the right of way this includes interception and diversion of water from the

road surface and subgrade. The installation of suitable surface and sub-surface drainage

system is an essential part of highway design and construction.

IMPORTANCE OF HIGHWAY DRAINAGE

Significance of Drainage

An increase in moisture content causes decrease in strength or stability of a soil mass

the variation in soil strength with moisture content also depends on the soil type and the mode

of stress application. Highway drainage is important because of the following reasons:-

x Excess moisture in soil subgrade causes considerable lowering of its stability the pavement

is likely to fail due to subgrade failure as discussed in Article 10.1.

x Increase in moisture cause reduction in strength of many pavement materials like

stabilized soil and water bound macadam.

x In some clayey soils variation in moisture content causes considerable variation in flume

of subgrade. This sometimes contributes to pavement failure.

x One of the most important causes of pavement failure by the formation of waves and

corrugations in flexible pavements is due to poor drainage.

x Sustained contact of water with bituminous pavements causes failures due to stripping of

bitumen from aggregates like loosening or detachment of some of the bituminous

pavement layers and formation of pot holes.

x In places where freezing temperatures are prevalent in winter, the presence of water in the

subgrade and a continuous supply of water from the ground water can cause considerable

damage to the pavement due in frost action.

x Erosion of soil from top of unsurfaced roads and slopes of embankment, cut and hill side is

also due to surface water.



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Requirements of Highway Drainage System

x The surface water from the carriageway and shoulder should effectively be drained off

without allowing it to percolate to subgrade.

x The surface water from the adjoining land should be prevented from entering the roadway.

x The side drain should have sufficient capacity and longitudinal slope to carry away all the

surface water collected.

x Flow of surface water across the road and shoulders and along slopes should not cause

formation of cress ruts or erosion.

SURFACE DRAINAGE

The surface water is to be collected and then disposed off. The water is first collected

in longitudinal drains, generally in side drains and then the water is disposed off at the nearest

stream, valley or water course. Cross drainage structures like culverts and small bridges may

be necessary for the disposal of surface water from the road side drains.

Collection of Surface Water

The water from the pavement surface is removed by providing the camber or cross

slope to the pavement. The rate of this cross slope is decided based on type of pavement

surface and amount rainfall.

where there is restriction of space, Construction of deep open drains may be undesirable. This

is particularly true when the road formation is in cutting. In such cases covered drains or

drainage trenches properly filled with layers of coarse sand and gravel may be used. In urban

roads because of the limitation of land width and also due to the presence of foot path,

dividing islands 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



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direction between the kerb and the pavement for short distances (See Fig. 4.9). This water

may be collected in catch pits at suitable intervals and lead through underground drainage

pipes. Section of a typical catch pit with grating to prevent the entry of rubbish into the

drainage system.

Drainage of surface water is all the more important in hill roads. Apart from the

drainage of water from the road formation, the efficient diversion and disposal of water

flowing down the hill slope across the road and that from numerous cross streams is an

important part of hill road construction. If the drainage system in hill road is not adequate and

efficient, it will result in complex maintenance problems.

Design of Surface Drainage System

The design of surface drainage system may be divided into two phases:

(i) Hydrologic analysi

(ii) Hydraulic analysis

Once the design runoff Q is determined, the next step is the hydraulic design of

drains. The side drains and partially filled culverts are designed based on the principles of

flow through open channels.

Data for Drainage Design

The following data are to be collected for the design of road side drain:

x Total road length and width of land from where water is expected to flow on the stretch of

the side drain.

x Run-off coefficients of different types of surfaces in the drainage area and their respective

areas (such as paved area, road shoulder area, turf surface, etc.)



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Designed Steps

Simplified steps for the design of longitudinal drains of a road to drain off the surface

water given below:

x The frequency of return period such as 10 years, 25 years etc. is decided based on

finances available and desired margin of safety, for the design of the drainage system.

x The values of coefficients of run-off C1, C2, C3 etc. from drainage areas A1, A2, A3

etc. are found and the weighted value of C is computed.

x Inlet time for the flow of storm water from the farthest point in the drainage area to

the drain inlet along the steepest path of flow is estimated from the distance, slope of

the ground and type of the cover. Figure 11.3 may be used for this purpose.

x Time of flow along the longitudinal drain T2 is. determined for the estimated length

of longitudinal drain L upto the nearest cross drainage or a water course and for the

allowable velocity of flow V in the drain i.e., T2 = L.

x The total time T for inlet flow and flow along the drain is taken as the time of

concentration or the design value of rain fall duration, T = T1 + T2.

x The required depth of flow in the drain is calculated for a convenient bottom width

and side slop of the drain. The actual depth of the open channel drain may be

increased slightly to give a free board. The hydraulic mean radius of flow R is

determined.

x The required longitudinal slope S of the drain is calculated using Manning‟s

formula adopting suitable value of roughness coefficient n.

Example 11.1

The distance between the farthest point in the turf covered drainage area (with an

average slope of 1.5 % towards the drain) and the point of entry to side drain is 200 m. The

weighted average value of the run-off coefficient is 0.25. The length of the longotudinal open



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drain in a sandy clay soil from the inlet point to the cross drainage is 540m. The velocity of

flow in the side drain may be assumed as 0.6 rn/sec so that silting and erosion are prevented.

Estimate the design quantity of flow on the side drain for a ten-years period of frequency of

occurrence of the storm.

Cross Drainage

Whenever streams have to cross the roadway, facility for cross drainage is to be

provided. Also often the water from the side drain is taken across by these cross drain in

order to divert the water away from the road, to a water course or valley. The cross drainage

structures commonly in use are culveris and small bridges. When a small stream crosses a road

with a linear waterway less than about six meter, the cross drainage structure provided is

called culvert; for higher values of linear waterway, the structure is called a bridge.

SURFACE DRAINAGE

Change in moisture content of subgrade are caused by fluctuations in ground water

table seepage flow, percolation of rain water and movement of capillary water and even water

vapour. In sub-surface drainage of highways, it is attempted to keep the variation of moisture

in subgrade soil to a minimum. However only the gravitational water is

drainage systems.

drained by the usual

Lowering of Water Table

The Highest level of water table should be fairly below the level of subgrade, in order

that the subgrade and pavement layers are not subjected to excessive moisture. From practical

considerations it is suggested that the water table should be kept atleast 1.0 to 1.2 m the

subgrade. In places where water table is high (almost at ground level at times) the best

remedy is to take the road formation on embankment of height not less than 1.0 to 1.2 meter.

When the formation is to be at or below the general ground level, it would be necessary to

lower the water table.



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UNIT 8 HIGHWAY ECONOMICS & FINANCE

INTRODUCTION

Better highway system provides varied benefits to the society. Improvements in

highway results in several benefits to the road users such as :

x Reduction in vehicle operational cost per unit length of road.

x saving travel time and resultant benefits in terms of time cost of vehicles and the passengers

x Reduction in accident rates.

x Improved level of service and ease of driving.

x Increased comfort to passengers.

Therefore he level of service of a road system may be assessed from the benefits to the

users

The improvement in road net work also benefits the land owner by providing better access

and consequently enhancing the land value. The cost of improvements in the highway of

land, materials, construction work and for the other facilities should be worked out. From the

point of view of economic justification for the improvements, the cost reductions to the

highway users and other beneficiaries of the improvements during the estimated period

should be higher than the investments made for the improvement. In the planning and design

of highways there is increasing need for analysis to indicate justification of the expenditure

required and the comparative worth of proposed improvements, particularly when various

alternatives are being compared.

The government or any other agency finances highway developments. The funds for

these are generally recovered 1ins the road users in the form of direct and indirect taxations.

Highway Finance

highway projects.

deals with various methods of raising and or providing money for the



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HIGHWAY USER BENEFITS

General Benefits

Several benefits are brought to highway users and others due to the construction of a

new highway or by improving a highway. Road user benefits are the advantages, privileges or

savings that accrue to drivers or owners through the use of one highway facility as compared

with the use of another. The various benefits due to highway improvement may be classified

into two categories: (i) quantifiable or tangible benefits in terms of market values and (ii) non

quantifiable or intangible benefits.

Quantifilab1e Benefits

Various benefits which can be quantified include benefits to road user such as

reduction in vehicle operation cost, time cost and accident cost. The other benefits include

enhancement in land value. These are briefly explained below:

x Saving in vehicle operation cost is due to reduction in fuel and oil consumption and

reduction in wear and tear of tyres and other maintenance costs. A road with sharp curves

and steep grades require frequent speed changes; presence of intersections require stopping

idling and accelerating; vehicle operation on road stretches with high traffic volume or

congestion necessitates speed changes and stopping and increased travel time.

Non-quantable Benefits

The non-quantifiable benefits due to improvements in highway facilities include

reduction in fatigue and discomfort during travel, increase in comfort and conveniences

improvement in general amenities, social and educational aspects, development of

and

recreational and medical services, improved mobility of essential services and defence forces,

aesthetic values, etc..

Motor Vehicle Operation Cost



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The factors to be considered for evaluating motor vehicle operation cost would differ

depending on the purpose of the analysis. The vehicle may be classified in different groups

such as passenger cars, buses, light commercial vehicles, single unit trucks combination

vehicles etc., for the purpose of cost analysis. The motor vehicle operation costs depend on

several factors which may be grouped .as given below:

x Cost dependent on time expressed as cost per year such as interest on capita depreciation

cost, registration fee, insurance charges, garage rent, driver‟s license salaries etc. as

applicable.

x Cost depending on distance driven expressed as cost per vehicle-kilometer. The items

which may be included here are fuel, oil, tyres, maintenance and repairs etc.

x Cost dependent on speed include cost of fuel, oil and tyre per vehicle-km-time-cost of

vehicles, travel time value of passengers, etc.

x Cost dependent on type of vehicle and its condition. Operation costs of larger vehicles are

comparatively higher. The operation cost of old vehicles maintained in poor condition is

also higher.

x Accident costs.

The costs of vehicle operation and time for unit distance may be taken as:

T = a+ (b+c) (14.1)

Speed

Where

a = running cost per unit distance, independent of journey time

b = a fixed hourly cost, dependent on speeds

c = the portion of the running cost which is dependent on speed

Therefore the operation costs may be considered to consist various components like motor

fuel cost, lubricating oil consumption, tyre costs, vehicle repair and maintenance,

depreciation, cost due to slowing, stopping, idling and standing delays, costs related to



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pavement surface and its condition, grades, curves and traffic volumes. Also the time costs

and accident costs are taken into consideration.

Example 14.1

Calculate the operating cost of a passenger car for 100 km length of a rural highway

with no sharp curves for most economical speed of vehicles operation using the following

HIGHWAY COSTS

General

The total Highway Cost for road user benefit analysis is the sum of the capital costs

expressed on an annual basis and the annual cost of maintenance. The total cost for highway

improvement is obtained from the estimate prepared from the preliminary plans. The total

cost of each highway engineering improvement proposal is calculated from the following five

components

(i) Right of way

(ii) Grading drainage, minor structures

(iii) Major structures like bridges

(iv) Pavement and appurtenances

(v) Annual cost of maintenance and operation

Computation of total annual highway cost based on summation of the annual cost of

individual items of improvements and their average useful lives is considered to be a proper

and accurate approach.It is difficult to estimate the service lives of highway elements as there

are several variables such as soil, climate topography and traffic. Road life studies enable

estimation of lives of pavements, bridges and other roadway facilities.

Annual Highway Cost

The items to be included while computing annual highway cost are



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(i) Administration (a portion) Personal service, building, equipment operation, office,

insurance etc.

(ii) Highway operation Equipment. building vehicle operation including capital costs of

vehicle.

(iii) Highway maintenance

(iv) Highway capital cost : Cost of highway components such as right of way, damage,

earthwork, drainage system. pavement bridges and traffic services depreciation cost

and interest on investment.

(v) Probable life and salvage value at the end of this period.

The average annual highway cost for a road system may be summed up by the

formula.

Ca – H + T + M + Cr

where

Ca = average annual cost of ownership and operation

H = average cost for administration and management at head quarters

T = average annual highway operation cost.

M = average annual highway maintenance cost.

Cr = average annual capital cost of depreciation of investment

capital or the capital recovery with return on capital

The annual cost is considered in the economic assessment of highway projects. Instead of

considering the overall cost of a project the annual repayment of a capital loan plus the

interest over a specified period of time of the annual capital cost is considered in the analysis.

The first cost of a capital improvement is converted into equivalent uniform annual cost by the

formula:



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i(1 - i)n

Cr = P (1+i)n-1 = P (CRF)

Where

Cr = receipt in a uniform series for n periods to cover P at a rate of

interest i

P = first cost of improvement of an element of a highway

i = rate of interest per unit period

n = period of time in number of interest periods

i(1 - i)n

CRF = Capital recovery factor = (1+i)n-1

At the end of the service life of road pavement, some of the items could be assigned

some salvage value. However the salvage value of some other items may be negligible.

The average annual capital cost Cr for a project considering salvage value may be

estimated by the use of the formula (for the capital-recovery with salvage value):

i(1 - i)n

Cr = (C-Vs) (1+i) n-1 + I Vs

= (C- Vs) CRF + i Vs (14.4)

Where C = total investment on construction

Vs = salvage value at the end of n years

i = interest rate applicable



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n = number of years of expected use of the facility

The compound amount accumulated sum S on the principal sum of proposed

improvement cost or single payment P, including interest rate, i in n years is given by:

s = P ( 1 + i)n (14.5)

economical proposal among various alternatives, in the analysis for economic justification of

the proposed improvement, it is required to use judgment such as quantitative selection of the

factors in which annual highway cost depends and the estimation of AADT of each class of

vehicle considering the normal increase in traffic and the generated traffic.

Methods of Analysis

The procedure for the economic evaluation of highway projects consists of

qualification for cost component and the benefits arising out of the project and to evaluate by

one of the methods of analysis.

There are several methods of economic analysis. Some of the common methods are.

Annual-cost Method, Rate-of-Return Method and Benefit-Cost Method.

Annual-Cost Method

The annual cost of each element of capital improvement is found by multiplying by

the appropriate CRF value calculated for the assume life span. The annual cost Cr may be

found using the relation (Eq. 14.3).

C1 = P. i(1+i)n = P(CRF)

(1+i)n-1

Rate-of-Return Method



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There are number of variations for the determination of raw of return of a highway

improvement. In the rate of return method, die interest rate at which two alternative solutions

have equal annual cost is found, If the rate of return of all proposed projects are known, the

priority for the improvement could be established.

Benefit Cost ratio Method

Principle of this method is to assess the merit of a particular scheme by comparing the

annual benefits with the increase in annual cost

Benefit cost ration = Annual benefits from improvement

Annual cost of the improvement

= R – R1

H1 - H

Where R = total annual road user cost for axisting highway

R1 = total annual road user cost for proposed highway

improvement

H = total annual cost of existing road

H1 = total annual cost of proposed highway improvement

The benefit-cost ratios are determined between alternate proposals and those plans dub

are not attractive are discarded. Then the benefit cost ratios for various increments of added

investment are computed to arrive at the best proposal. hi order to justify the proposed

improvement, the ratio should be greater than 1.0. However, the choice of interest rate would

affect the results of the benefit-cost solutions.

Total annual road user cost for proposal B = RB = Rs. 2491,125



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Benefit-cost ratio,

B = RA-RB = 3081,330 - 2491.125 = 590,205 = 2.874

A HB-HA 381,900 - 176,527 205, 373

Total annual highway cost of proposal C = HC = Rs.3,75,100

Total annual highway cost of proposal C= HC = Rs.2377,245

Benefit – cost ratio,

C = RA-RB = 3081,330 - 2377.245 = 704,085 = 3.546

A HC-HA 375,100 - 176,527 198, 573

Therefore, alternative C is the best one with higher benefit-cost ratio.

HIGHWAY FINANCE

Basic principle in highway financing is that the funds spent on highways are

recovered from the road users. The recovery may be both direct and indirect.

Two general methods of highway financing are:

Pay-as-you-go method

Credit financing method

In pay-as-you-go method, the payment for highway improvements, maintenance and

operation is made from the central revenue. In credit financing method, the payment for

highway improvement is made from borrowed money and this amount and the interests are

re-paid from the future income.



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Distribution of highway cost

The question of distributing highway cost among the Government, road-user and

other has been a disputed task in several countries. Many economists are of the view that the

financial responsibility for roads should be assigned only among the beneficiaries on the

basis of the benefit each one receives.

There are several theories suggesting the method of distribution of highway taxes

between passenger cars and other commercial vehicles like the trucks. However in India the

annual revenue from transport has been much higher than the expenditure on road

development and maintenance. Therefore there is no problem of distributing the highway cost

among other agencies. Also the taxation on vehicles is being considered separately by the

states and there seems to be no theory followed for the distribution of taxes between various

classes of vehicles.

Sources of Revenue

The various sources from which funds necessary for highway development and

maintenance may be made available, are listed below:

Taxes on motor fuel and lubricants.

Duties and taxes on new vehicles and spare part including tyres

Vehicles registration tax.

Special taxes on commercial vehicles

Other road user taxes

Property taxes

Toll taxes

Other funds set apart for highways

There should be an equitable distribution of revenues available for highways.



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Highway financing in India

The responsibility of financing different roads lies with the Central Government, State

Governments and local bodies including Corporations, Municipalities, District Boards and

Panchayats.

Taxes levied by Central Government for highway financing are:

Duties arid taxes on motor fuel

.Excise duty on vehicles and spare parts, tyre etc.

Excise duty on oils, grease, etc

Taxes levied by the State Governments include:

Registration fees for vehicles and road tax

Permits for transport vehicles

Passenger tax on buses

Sales tax on vehicle parts tyre etc.

Fees on driving licenses

Taxes levied by local bodies are mainly the toll tax.

Ever since the introduction of Central Road Fund (CRF) in the year 1929 by taxing motor

fuel, this has been the main source of finance for the State Government to meet the road

development needs, without having to go through the time consuming process of special

sanctions each time. However of late the CRF is also being merged with the general revenue,

in March 1976 the Lok Sabha has passed the resolution Of the Ministry of Transport ensuring

the existence of the CRF separately with the specified objectives. An Amount of not less

than 3.5 paise per litre out of the duty of customs and excise on motor spirit would be set

apart towards the CRF for the road development. While utilizing this fund, greater attention



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would be given to schemes of all-India importance. Twenty percent of the fund would be

retained by the central Government as reserve. The fund will also be used for road research

schemes, traffic studies, economics surveys and training arrangements for young engineers.

The gross revenue from road transport in India during the sixth plan period 1978-83, 1980-85

was about Rupees l2,000 Crores



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Civil v Transportation Engineering Unit 1,2,3,4,5,6,7,8

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