Transportation Engineering - I - · PDF fileenough to Transportation Engineering - I nissan...

2013

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First edition: 11/13/2013

enough to

Transportation Engineering - I

enough to Transportation Engineering - I nissan

2 Notes by : Shambhu Kumar Shah

Contents

[1] INTRODUCTION TO TRANSPORTATION ENGINEERING 3

MODES OF TRANSPORTATION 3

ROLE OF ROAD TRANSPORTATION IN RURAL DEVELOPMENT OF NEPAL 5

[2] HISTORICAL DEVELOPMENT OF HIGHWAY 6

CLASSIFICATION OF ROADS IN NEPAL 6

HISTORICAL DEVELOPMENT OF ROAD CONSTRUCTION 7

ROAD CONSTRUCTION IN NEPAL 9

[3] HIGHWAY PLANNING 10

OBJECTIVES OF HIGHWAY PLANNING 10

PLANNING SURVEYS 10

HIGHWAY ALIGNMENT 11

ENGINEERING SURVEYS AND ITS STAGES 13

[4] GEOMETRIC DESIGN OF HIGHWAY 15

INTRO 15

BASIC DESIGN CONTROL AND CRITERIA 15

ELEMENTS OF HIGHWAY CROSS-SECTION 16

[5] HILL ROADS 47

SPECIAL CONSIDERATION IN THE ALIGNING OF HILL ROADS 47

HILL ROAD DESIGN 48

DESIGN OF HAIR PIN BEND 49

DESIGN AND CONSTRUCTION OF HILL ROADS 51

CONSTRUCTION PROBLEMS IN HILL ROADS 52

DRAINAGE IN HILL ROADS 53

STRUCTURES IN HILL ROADS 54

PASSING LANE IN HILL ROADS 55

[6] HIGHWAY DRAINAGE 56

IMPORTANCE OF HIGHWAY DRAINAGE 56

REQUIREMENTS OF HIGHWAY DRAINAGE SYSTEM 56

CLASSIFICATION OF HIGHWAY DRAINAGE SYSTEM 56

EROSION CONTROL AND ENERGY DISSIPATING STRUCTURE 60

[7] HIGHWAY MATERIALS 63

CLASSIFICATION OF MATERIALS 63

DESIRABLE PROPERTIES OR ROAD AGGREGATES 63

TEST FOR ROAD AGGREGATES 64

GRADATION ANALYSIS OF AGGREGATE 67

BITUMINOUS MATERIALS 68

[8] GREEN ROADS 76


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[1] INTRODUCTION TO TRANSPORTATION ENGINEERING

Transportation

A transportation system may be defined as consisting of the fixed facilities, the flow

entities and the control system.

- Transportation contributes to the economic, industrial, social and cultural development of any

country.

- 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.

- The adequacy of transportation system of a country indicates its economic and social

development.

Advantages

The advantages of transportation may be summarised as follows:

i) It is for advancement of the community.

ii) It is essential for the economic prosperity and general development of the country.

iii) It is essential for strategic movement in emergency for defence of the country and to

maintain better law and order.

iv) It is essential for the improvement of rural areas by improving facilities for education,

health, business and other social needs in villages.

Modes of transportation

Following are the major modes of transportation.

A. Primary Modes 1. Roadways or Highways 2. Railways 3. Waterways

i) Inland ii) Coastal iii) Ocean

4. Airways i) Domestic ii) International

B. Secondary Modes 1. Ropeways 2. Pipelines

i) Water ii) Gas iii) Sewer

3. Canals i) Irrigation Canal ii) Storm water drainage ditch

4. Belt conveyers

(a) Roadways or Highways

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

and all.

- 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.

- It is possible to provide door to door service only by road transport.

- The other three modes, viz. airways, waterways and railways have to depend on transportation

by roads for the service to and from their respective terminals, airports, harbours or stations.



- The roads or highways not only include the modern highway system but also to provide

independent facilities for road travel by a well-planned network of road throughout the country,

feeder roads, city roads, village roads and pedestrians. But other modes do not provide such

type of more facilities.

(b) Railways

The transportation along the railway track could be advantageous by railway between

the stations both for the passenger and goods, particularly for longer distances.

- The energy requirement to haul unit load through unit distance by railway is only a fraction (¼th -

⅙th) of that required by road.

- Hence full advantage of this mode should be taken for the transportation of bulk goods along

land where the railway facilities are available.

(c) Waterways

Transportation by water is the slowest among the four modes; but this mode needs

minimum energy to haul unit load through unit distance.

- The transportation by water is possible between the parts on the sea routes or along the rivers

or canals where inland transportation facilities are available.

(d) Airways

The transportation by air is the fastest among four modes.

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

passengers and the goods between airports.

Advantages and Limitations of Highway over other Modes

Advantages

i) Roads are used by various types of vehicles; like passenger cars, buses, trucks, two and

three automobiles, cycles etc. But railway tracks are used only by rail locomotives and

wagons; waterways are used only by ships and boats.

ii) Road transport requires relatively small investment, since motor vehicles are much

cheaper than other carriers like rail locomotives and wagons, water and air carriers.

iii) Construction and maintenance of roads are also cheaper than that of railway tracks, docks,

harbours and airports.

iv) Road transport offers a complete freedom to road users to transfer the vehicle from one

lane to another. This flexibility of changes in location, direction, speed and timing of travel

is not available to other modes of transport.

v) In particular for short distance travel, road transport saves time.

Disadvantages

i) Road transport is subjected to a high degree of accidents due to flexibility of movements

offered to the road users, than other modes of transportation.

ii) It consist more land coverage and also takes more area for parking.

iii) It is more energy consuming and environmental polluting than other modes.



Role of Road Transportation in Rural Development of Nepal Since, over 80% population of the country living in the villages, the development in

urban areas alone do not indicate the overall development of the country.

- Only with the improvement in transportation facilities in rural areas, there could be faster

development of rural centres.

- The fertilizers and other inputs for agriculture and cottage industries could reach the rural

population easily and similarly the products can be sold at the nearest marketing centres for

more remunerative price resulting in faster economic growth and decreased wastage.

- Through the proper facility of transportation, the education, health care and other social needs

in the village are increased and hence migration to urban centres decreases. Due to increase of

such facilities helping in balance development of the country.



[2] HISTORICAL DEVELOPMENT OF HIGHWAY

Classification of Roads in Nepal According to Nepal Road Standard (NRS), the roads are classified as:

1. Classification by traffic flow 2. Classification by service

1. Classification by Traffic flow

Class Types of Carriageway Types of category Traffic

volume / day

Class IAA 4-lanes divided by 2x2x3.5m with central median, Asphalt concrete or cement concrete

a) Level b) Rolling c) Mountainous

7000 5000 3000

Class IA 2-lanes 3.5m width with bituminous premixed wearing course


3000 2500 1500

Class I 2-lanes 2x3.5m width with surface treatment


1500 1000 300

Class II Single lane 3.5m width with surface treatment


300 150 75

Class III Single lane 3.5m width with gravel Any topography 75

2. Classification by Services i) National Highways (NH) ii) Feeder Roads (FR) iii) District Roads (DR) iv) Urban Roads (UR) v) Village Roads (VR)

(i) National Highways

National Highways are main highways connecting East to West and North to South of

the country. The road connecting National Highways to regional headquarters shall also be

classified as National Highways.

- These serve directly the greater portion of the longer distance travel, provide consistently higher

level of service in terms of travel speeds and bear the inter-community mobility.

- These roads shall be the main arterial routes passing through the length and breadth of the

country as a whole.

(ii) Feeder Roads

Feeder Roads are important roads of localised nature, which connect district

headquarters and/or zonal headquarters to National Highways.

- Feeder roads are of secondary nature in the hierarchy of the road network.

- It is further classified into: (a) Feeder Roads Major (FRN)

(b) Feeder Roads Minor (FRO)



a) Feeder Roads Major

- Major Links (i.e. with an AADP of over 100 vehicles/day) between the National highways.

- Road linking district headquarters / zonal headquarters to the national highway.

- Links form National highways to the major places of industry, tourism, public utilities

and power generation (e.g. hydropower) etc.

b) Feeder Roads Minor

- Links from feeder roads (FRN) to the major places of industry, tourism, public utilities

and power generation.

- Links from urban roads to the major places of industry, tourism, public utilities and

power generation (e.g. hydropower).

(iii) District Roads

This class of roads consisting of all roads not defined as ‘National Highways’ or ‘Feeder’

and ‘City’ Roads.

- These roads should give access to one or more villages to the nearest market or to higher types

of roads.

- Moderate travel speeds are typical on such roads.

(iv) Urban Roads

These include roads within the urban limits except for the above classes, passing

through the city.

- These provide access to abutting residential, business or industrial properties.

(v) Village Roads

Village roads include short, non-through roads linking single village directly to the district

roads.

Note: There are 15 highways and over 51 feeder roads completed or under construction in

Nepal with a total length of over 5400 km. (as per NRS 2nd revision).

Historical Development of Road Construction

The Oldest mode of travel was on the footpaths. Animals were also used to

transport men and material. Later simple animal drawn vehicles were developed and

these become a common and popular mode of transportation for a very long period

after the invention of wheel.

The Romans constructed an extensive system of roads radiating in many

directions from Rome though the Empire mainly for military operations.

Following are historical road construction, which may have developed one after

another:

1. Roman Roads 2. Tresagut construction

3. Metcalf construction 4. Telford construction

5. Macadam construction



(a) Roman Roads

Construction steps

(i) A trench of width equal to that of the carriageway was dug along a straight path by removing

loose soil from top. The trench was cut up to a depth until a hard stratum was reached.

(ii) One or two layers of large foundation stones of thickness ranged from 10 to 20 cm were laid in

lime mortar at the bottom. Vertical kerb stone were placed along the edges of the pavement.

(iii) A second layer of lime concrete with large size broken stone of thickness 25 to 40 cm in lime

mortar was laid over the bottom course.

(iv) The wearing courses consisting of dressed large stone blocks set in lime mortar to a thickness

varied from 10 to 15 cm was provided.

(b) Telford construction



(e) Macadam construction

Construction steps

(i) Subgrade is compacted and prepared with cross slope of 1 IN 36 up to a desired width (about 9

m).

(ii) Broken stones of a strong variety, all passing through 5 cm size sieve were compacted to a

uniform thickness of 10 cm.

(iii) The second layer of strong broken stones of size 3.75 cm was compacted to thickness of 10 cm.

(iv) The top layer consisted of stones of sizes less than 2 cm compacted to a thickness of about 5 cm

and finished so that the cross-slope of pavement surface was also 1 in 36.

Road Construction in Nepal Road construction in Nepal has been rather haphazard. The main reason of this is

probably that the responsibility of planning, construction and maintenance has been shared by

more than one agency such as VDC, DDC, DOR, municipalities etc.

- Construction and maintenance of major and important roads like National highways and Feeder

roads are carried out by DOR (department of road).

- Many wide roads with hard surface in Nepal (particularly in Kathmandu) may have been

developed during Malla’s period. These roads were basically intended to horse driven carts.

These roads consisted of hard broken brick over which flag stone slabs were laid over a base of

lime concrete.

- The Trubhuwan Rajpath connecting Kathmandu to Bhaise on the old BhimphendiAmlekhganj

was built under Indian government in 2013 B.S.

- Kathmandu was connected to the outside world by motor able road in the period of 2007 to

2024 B.S.

- In 2012 B.S., the 77 km HetaudaNarayangadh road was taken up and completed in 2015 B.S.

- In 2007 to 2032 B.S., the road development strategy was adopted for the country continues,

with the feeder roads to the interior mountain areas of the North and Terai towns in the south

expanding gradually.

- The eastern section of East-west highway was successfully completed on the mid of 2027 B.S.

and links to Pokhara from south as well as Ktm.

- In the following of East-west highway i.e. up to 2042 B.S., east of Nepalganj was completed with

significant section of North-south routes and connection with East-west highway.



[3] HIGHWAY PLANNING

Intro

Planning is the process of thinking before doing or simultaneously with the progress of

work.

- One of the main objectives of planning is to utilize the available resources in the best possible

way and in very systematic manner including project identification and decision of national

priority area.

Objectives of Highway Planning

(i) To plan a road network for efficient and safe traffic operation, but at minimum cost.

(ii) To arrive at the road system and the lengths of different categories of roads, this could provide

maximum utility and could be constructed within the available resources during the plan

period under consideration.

(iii) To fix up date wise priorities for development of each road link based on utility of the project.

(iv) To plan for future requirements and improvements of roads in view of anticipated

developments.

Planning Surveys Highway planning survey phases includes:

1) Assessment of road length requirement for an area

2) Preparation of master plan showing the phasing of plan in annual and or five year plans

The planning surveys consist of the following studies;

(a) Economic studies (b) Traffic or road use studies (c) Financial studies (d) Engineering studies

a) Economic studies

It includes:

i) Population and its distribution in each village, town or other locality with the area classified

in groups.

ii) Trend of population growth.

iii) Agricultural and industrial products, their development and future trends.

iv) Per capita income.

b) Financial studies

It includes:

i) Source of income and estimated revenue from taxation on road transport.

ii) Living standards.

iii) Resources at local level, vehicle registration and fines.

iv) Future trends in financial aspects.

c) Traffic or Road use studies

It includes:

i) Traffic volume in vehicles/day, AADT (annual average daily traffic), peak and design hourly

traffic volume.



ii) Traffic flow patterns. iii) Mass transportation facilities.

iv) Accidents, their cost analysis and cause. v) Future trends and growth in traffic volume.

d) Engineering studies

It includes:

i) Topographic surveys ii) Soil surveys iii) Location and classification of

existing roads

iv) Road life studies v) Traffic studies vi) Special problems in drainage, construction

and maintenance of roads.

Highway Alignment The position or the layout of the centre line of the highway on the ground is called

alignment.

- The horizontal alignment includes the straight path, the horizontal deviations and curves.

- Vertical alignment includes change in gradient and vertical curves.

The improper alignment would result in one or more of the following disadvantages:

(i) Increase in construction cost (ii) Increase in maintenance cost

(iii) Increase in vehicle operation cost (iv) Increase in accident rate

Requirements of highway alignment

The basic requirements of an ideal alignment between two terminal stations should be:

(i) Short (ii) Easy (iii) Safe (iv) Economical

1. Short

A straight alignment would be the shortest, though there may be several practical

considerations which would cause deviations from the shortest path.

2. Easy

The alignment should be such that it is easy to construct and maintain the road with

minimum problems. Also the alignment should be easy for the operation of vehicles with easy

gradients and curves.

3. Safe

The alignment should be safe enough for construction and maintenance from the view

point of stability of natural hill slopes, embankment and cut slopes and foundation of

embankments.

- Also it should be safe for the traffic operation with safe geometric features.

4. Economical

The road alignment could be considered economical only if the total cost including initial

cost, maintenance cost and vehicle operation cost is lowest.

The alignment should be such that it would offer maximum utility by serving maximum

population and products.



Factors controlling highway alignment The various factors which control the highway alignment in general may be listed as:

1. Obligatory points 2. Traffic

3. Geometric design 4. Economy

5. Other consideration

Additional cares for hill roads are:

1. Stability 2. Drainage 3. Geometric standard 4. Resisting length

1. Obligatory Points

There are control points governing the alignment of the highways. These control points

may be divided broadly into two categories:

(i) Points through which the alignment is to pass

(ii) Points through which the alignment should not pass

(i) Obligatory points through which the road alignment has to pass may cause the alignment to

often deviate from the shortest or easiest path. E.g. bridge site, intermediate town.

The road approaches at the bridge site should not be curved near the bridge and as far

as possible skew crossing should be avoided. Thus in order to locate a bridge across a river

the alignment may have to be changed.

(ii) Obligatory points through which the road should not pass also make it necessary to deviate

from the proposed shortest alignment. The obligatory points which should be avoided while

aligning a road include religious places, very costly structures, unsuitable land etc.

A lake, pond or valley which falls on the path of a straight alignment will also necessitate

the alignment to deviate from the straight path and go round along the grade line.

2. Traffic

The alignment should suit traffic requirements. The new road to be aligned should keep

in view the desired lines, traffic flow patterns and future trends.

3. Geometric Design

Geometric design factors such as gradient, radius of curve and sight distance also would

govern the final alignment of the highway. As far as possible while aligning a new road, the

gradient should be flat and less than the ruling or design gradient.

Thus it may be necessary to change the alignment in view of the design speed, maximum

allowable super-elevation and coefficient of lateral friction.

4. Economy

In working out the economics, the initial cost, the maintenance cost, the vehicle

operation cost should be taken into account. The initial cost of construction can be decreased if

high embankment & deep cuttings are avoided and the alignment is chosen in a manner to

balance the cutting and filling.

5. Other considerations

Various other factors which may govern the alignment are drainage considerations,

hydrological factors, political considerations and monotony. The subsurface water level, seepage

flow and high flood level are the factors to be kept in view.



Engineering Surveys and Its Stages Engineering surveys are to be carried out in following four stages:

1. Map study 2. Reconnaissance

3. Preliminary surveys 4. Final location & Detailed surveys

1. Map Study With the help of topographic map, the possible route of road can be aligned.

Topographic map provides the details of rivers, hills, valleys etc.

- The probable alignment can be located on the map from the following details available on the

map:

i) Alignment avoiding valleys, ponds or lakes.

ii) When the road has to cross a row of hills, possibility of crossing through a mountain pass.

iii) Approximate location of bridge site for crossing rivers, avoiding bend of the river (if any).

iv) When a road is connected between two stations, one of the top and other on the foot of the

hill then alternative routes can be suggested keeping in view the permissible gradient say

ruling gradient.

2. Reconnaissance The second stage of survey for highway location is the reconnaissance to examine the

general character of the area for deciding the most feasible routes for detailed studies.

Some of the details collected during reconnaissance are given below:

i) Valleys, ponds, lakes, marshy lands, hills, permanent structures and other obstructions along

the route which are not available in the map.

ii) Approximate values of gradient, length of gradient and radius of curves of alternate alignment.

iii) Number and type of cross drainage structures, maximum flood level and natural ground water

level along the probable routes.

iv) Soil type along the routes geological features.

v) Sources of construction materials, water and location of stone quarries.

3. Preliminary Survey It is a large scale study of one or more feasible routes.

Objectives

The main objectives of preliminary survey are:

i) To survey the various alternate alignments proposed after the reconnaissance.

ii) To collect all the necessary physical information and details of topography, drainage and soil.

iii) To compare the different proposals in view of the requirements of a good alignment.

iv) To estimate quantity of earth work materials and other construction aspects and to work out

the cost of alternate proposals.

v) To finalise the best alignment from all considerations.

Methods of Preliminary Survey

The preliminary survey may be carried out by only one of the following methods:

A. Conventional Method

In this method, a survey party carries out surveys using the required field equipment,

taking measurements, collecting topographical & other data and carrying out soil surveys.



Following procedure is done in the conventional method:

(i) Primary traverse (ii) Topographical features (iii) Levelling work (iv) Drainage studies and Hydrological data

(v) Soil survey (vi) Material survey (vii) Traffic survey (viii) Determination of final centre line

B. Aerial Method

Aerial photographic surveys are very much suited for preliminary surveys, especially

when the distance and area to be covered are vast.

The survey may be divided into the following steps:

(i) Taking aerial photographs of the strips of land to be surveyed, with the required longitudinal

and lateral overlaps.

(ii) The photographs are examined under stereoscope and control points are selected for

establishing the transverse of the alternate proposals.

(iii) Using stereo-pair observations, the spot levels and subsequently contour lines may be

obtained.

(iv) Photo-interpolation methods are used to assess the geological features, soil conditions,

drainage requirements etc.

4. Final Location and Detailed Survey These serves dual purposes i.e. first located on the field by establishing the centre line.

Next detailed survey should be carried out for collecting the information necessary for the

preparation of plan and construction details for the highway project.

Location

The centre line of the road finalised in the drawings is to be translated on the ground

during the location survey. This is done by using a transit theodolite and by staking of the centre

line.

- Major and minor control points are established on the ground and centre pegs are driven,

checking the geometric design requirements.

- The centre line stakes are driven at suitable intervals, say 50m in plain and rolling terrain and

20m in hilly terrain.

Detailed survey

Temporary Bench Marks are fixed at intervals of about 250m and at all drainage and

under pass structures. Levels along the final centre line should be taken at all staked points.

- Levelling work is of great importance as the vertical alignment, earthwork calculations and

drainage details are to be worked out from the level notes.

- The cross-section levels are taken up to desired width, at intervals of 50 - 100 m in rolling terrain

and 20 m in hilly terrain.

- All topographical details are noted down and also plotted using conventional signs.

- Adequate hydrological details are also collected and recorded.

- A detailed soil survey is carried out to enable drawing of the soil profile.

- The depth up to which soil sampling is to be done may be 1.5 - 3 m below the ground level or the

finished grade line of the road whichever is lower.

- CBR value of soils along the alignment may be determined for designing the pavement.



[4] GEOMETRIC DESIGN OF HIGHWAY

Intro The geometric design of a highway deals with the dimensions and layout of visible

features of the highway such as alignment, sight distance and intersections.

- The geometry of highway should be designed to provide optimum efficiency inn traffic

operations with maximum safety at reasonable cost.

Geometric design of highway deals with following elements:

i) Cross section elements ii) Sight distance consideration iii) Horizontal alignment details

iv) Vertical alignment details v) Intersection elements

Basic Design Control and Criteria The geometric design of highway depends on several design factors. The important of

these factors which control the geometric elements are:

i) Design speed ii) Topography iii) Traffic factors

iv) Design hourly volume and Capacity v) Environmental and Other factors

(i) Design Speed

It is the maximum permissible safe speed of light vehicle on a given road considered for

the design of road elements.

factors affecting choice of design speed

Type of highway Nature of terrain Traffic volume

Speed capabilities of vehicle Ability of person driving the vehicle Level of economic development of the Nation

Various geometric designs i.e. cross section element, horizontal alignment elements,

vertical alignment elements etc. all mainly depend upon design speed.

(ii) Topography

The topography or the terrain conditions influence the geometric design of highway

significantly. The terrains are classified based on the general slope of the country across the

alignment, as plain, rolling, mountainous and steep terrain.

- In hilly terrain, it is necessary to allow for steeper gradients and sharper horizontal curves due to

the construction problems.

(iii) Traffic Factors

The traffic factors that affect the geometric design of roads are the vehicular

characteristics and human characteristics of road users.

- It is difficult to decide the design vehicle or the standard traffic lane due to mixed traffic flow

conditions.

- The different vehicle classes such as passenger cars, buses, trucks, motor cycles etc. have

different speed and acceleration characteristics.

- The important human factors which affect traffic behaviour include the physical, mental and

psychological characteristics of driver and pedestrians.



(iv) Design Hourly Volume and Capacity

The traffic flow or volume keeps fluctuating with time, from a low value during off-peak

hours to the highest value during the peak hour.

- It will be uneconomical to design the roadway facilities for the peak traffic flow or the highest

hourly traffic volume.

- Hence, a reasonable value of traffic volume is decided for the design and this is called the design

hourly volume.

(v) Environmental and Other Factors

The environmental factors such as landscaping, air pollution, noise pollution and other

local conditions should be given due consideration in the design on road geometrics.

Elements of Highway Cross-section The elements of geometric design include:

1. Elements of Cross-section 2. Elements of horizontal alignment

3. Elements of vertical alignment

1. Elements of Cross section

The main x-sectional elements are:

i) Traffic lane ii) Carriage way or width of pavement iii) Shoulder iv) Road way v) Width of formation

vi) Side slope of fill or cut vii) Lay bays viii) Right of way or land width ix) Camber x) Super-elevation

(i) Traffic Lane

The carriage way intended for one line of traffic movement may be called a traffic lane.

- The lane width is determined on the basis of the width of vehicle and the minimum side

clearance which may be provided for the safety.

- A width of 3.57 m is considered desirable for a road having single lane for vehicles of

maximum width 2.44 m.

- The number of lanes required in a highway depends upon the predicted traffic volume and

the design traffic volume of each lane.



(ii) Carriageway or Width of Pavement

The width of road on which the vehicles move is called pavement width or carriageway,

which depends upon the width of traffic lane and number of lane.

- The lane width is determined on the basis of the width of vehicle and the minimum side

clearance which may be provided for the safety.

Carriageway width (as per NRS)

(a) Single lane → 3.75 m

(b) Intermediate lane → 5.5 m

(c) Two lane without raised kerb → 7.0 m

(d) Two lane with raised kerb → 7.5 m

(e) Multilane carriageway → 3.5 m (width per lane)

Notes:

(i) On district roads, the carriageway width of single lane may be restricted to 3 m normally.

Width greater than 3 m may however be adopted judiciously depending on the type and

intensity of traffic, cost and related factors.

(ii) Except on important Nation Highways, an intermediate carriageway width of 5.5 m may also

be adopted instead of regular two lanes if the same is considered advantages.

(iii) The carriageway width for intermediate lane shall vary from 5 - 6 m.

(iii) Shoulders

Shoulders are provided along the road edge to serve as an emergency lane for vehicle

compelled to be taken out of the pavement or roadway.

- Shoulders also act as service lanes for vehicles that have broken down.

- The width of shoulder should be adequate to accommodate stationary vehicle fairly away

from the edge of adjacent lane.

- The shoulders should have sufficient load bearing capacity to support loaded truck even in

wet weather.

- The surface of the shoulder should be rougher than traffic lanes so that vehicles are

discouraged to use the shoulders as a regular traffic lane.

- The colour of the shoulder should preferably be different from that of the pavement so as to

be distinct.

Shoulder width (as per NRS)

Types of carriageway Total shoulder width in m (both sides included) i) Two & four lanes (black topped) ii) Single lane (surface dressed) iii) Single lane (gravelled surface)

4 – 6 m 4 – 5 m 3 – 5 m

(iv) Width of Formation or Roadway

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

including separators if any and the shoulders.

- Formation or roadway width is the top width of the highway embankment or the bottom

width of highway cutting excluding the side drains.

- In multilane highways, roadway width should be adequate for the requisite number of traffic

lanes besides shoulders and central median.

- The minimum roadway width on single lane bridge in 4.25 m.



(v) Lay-bays

Lay-bays are provided near public conveniences with guide maps to enable drivers to

stop clear off the carriageway.

- Lay-bays should normally be of 3 m width and at least 30 m length with 15 m end tapers on

both sides.

(vi) Right of Way or Land Width

Right of way is the area acquired for the road, along its alignment. The width of this

acquired land is known as land width and it depends on the importance of the road and

possible future development.

- The land width is governed by the following factors:

i) Width of formation, road margins

ii) Height of embankment or depth of cutting

iii) Side slopes of embankment or cutting

iv) Drainage system and their size

v) Rainfall, topography and runoff

vi) Sight distance considerations on horizontal curves

Right of Way (as per NRS)

Road Category Right of way Between building lines a) Trunk Roads b) Feeder Roads c) District Roads

50m (25m on either side of road centre line) 30m (15m on either side of road centre line) 20m (10m on either side of road centre line)

62 m 42 m 32 m

(vii) Camber

Camber or cross slope is the slope provided to the road surface in the transverse

direction to drain off the rain water from the road surface. Drainage and quick disposal of water

form pavement surface by providing camber is necessary for following reasons:

To prevent the entry of surface water into the sub-grade soil through pavement; the stability,

surface condition and the life of the pavement get adversely affected if the water enters in the

subgrade and the soil gets soaked.

To prevent the entry of water into the bituminous pavement layers, as continued contact with

water causes stripping of bitumen from the aggregates and results in deterioration of pavement

layer.

To remove the rain water from the pavement surface as quickly as possible to allow the

pavement to get dry soon after the rain; the skid resistance of the pavement gets considerably

decreased under wet condition, rendering it slippery and unsafe for vehicle operation at high

speed.

- Usually the camber is provided on straight roads by raising the centre of the carriageway w.r.t.

edges, forming a crown or highest point on the centre line.

Camber (as per NRS)

i) Earthen road : 5 % ii) Gravel road : 4 % iii) Bitumen (rural area) : 3 % iv) Bitumen (urban area) : 2.5 %



Shape of Camber

Following are the shapes of camber generally adopted:

a) Parabolic Shape or Elliptic shape

b) Straight line camber c) Combination of Straight and Parabolic Shape

Parabolic or Elliptic shape is given so that the profile is flat at the middle and steeper

towards the edges, which is preferred by fast moving vehicles as they have to frequently cross

the crown line during overtaking.

When very flat cross slope is provide as in cement concrete pavements, straight line

shape of camber may be provided.

Disadvantages of too steep cross slope (Heavy Camber)

Too steep cross slope is not desirable because of the following reasons:

Discomfort causing throw of vehicle when crossing the crown during overtaking operations.

Problems of toppling over of highly laden bullock carts and trucks.

Formation of cross ruts due to rapid flow of water.

Tendency of most of the vehicles to travel along the centre line.

(viii) Super-elevation

The transverse inclination throughout the length of horizontal curve by raising outer

edge counteract w.r.t. inner edge, in order to counteract the effect of centrifugal force, is known

as super-elevation (or cant or banking).

The super-elevation ‘e’ is expressed as the ratio of height of outer edge w.r.t. the

horizontal width, i.e.

or, e =

is very small and value of 0.07 (7 %)

Analysis for Expression of Super-elevation

Consider a vehicle moving at a speed of v m/s on a circular curve having radius ‘R’.



The following forces acting on the vehicle:

i) Centrifugal force (P) acting horizontally through the centre of gravity (CG) of vehicle

ii) The weight (W) of the vehicle action vertically downwards through the C.G. of the vehicle

iii) The frictional force (FA & FB) developed between the wheels and pavement, transversely along

the pavement surface.

and

Where,

or = frictional resistance between wheel and pavement

f = coefficient of friction

Considering equilibrium, the component of centrifugal force parallel to the pavement

(pcosθ) is opposed by component of weight parallel to the pavement and frictional force and

, i.e.

Here, Coefficient of lateral friction ( f ) = 0.15

Maximum value of super-elevation (tanθ) = 0.07 (7 %)

Here, e = rate of super-elevation = tanθ

If the speed of vehicle is represented as V kmph then,

Note:

If coefficient of lateral friction is ignored,



Types of Super-elevation

There are two types of super-elevation:

i) Minimum Super-elevation

If the value of super-elevation required from equation,

, comes out to be less

than the usual camber provided to the road surface, the super-elevation provided will be

equal to amount of camber so as to facilitate the drainage of surface water. This lower limit

of super-elevation is referred as minimum super-elevation.

ii) Maximum Super-elevation

In a highway with mixed traffic the maximum value of super-elevation (7 %) so as to

avoid the danger of overturning is known as maximum super-elevation.

Steps for Super-elevation Design

Following are the steps for designing super-elevation:

Step (i): The super-elevation for 75 % of design speed (v m/s or V kmph) is calculated

neglected the friction.

Step (ii): If the calculated value of ‘e’ is less than 7 % or 0.07 the value so obtained is

provided. If the value of ‘e’ as per equation (i) exceeds 0.07 then provide the

maximum super-elevation = 0.07

Step (iii): Check the coefficient of friction developed for the maximum value of e = 0.07 at the

full value of design speed.

If value of ‘f ’ thus calculated is less than 0.15, the super-elevation of 0.07 is safe

for the design speed. If not, calculate the restricted speed as given in Step (iv).

Step (iv): As an alternative to Step (iii), the allowable speed ( m/s or kmph) at the curve is

calculated by considering the design coefficient of lateral friction and the maximum

super-elevation.

Calculate the safe allowable speed,

√ √

√

If the allowable speed, as calculated above is higher than the design speed, then

the design is adequate and provides a super-elevation of ‘e’ equal to 0.07.



Method of Obtaining Super-elevation

Introducing super-elevation on a horizontal curve in the field is an important feature in

construction. The full super-elevation is attained by the end of transition curve or at the

beginning of the circular curve.

The attainment of super-elevation may be split up into two parts:

i) elimination of crown of the cambered section

ii) Rotation of pavement to attain full super-elevation

i) Elimination of crown of the cambered section

This may be done by two methods:

Method 1

In this method, the outer half of the cross-slope is rotated about the crown at a desired

rate such that the surface falls on the same plane as the inner half and the elevation of the

centre line is not altered.

- The outer half of the cross-slope is brought to level or horizontal at the start of the transition

curve or at tangent point (T.P.). Subsequently the outer half is further rotated so as to obtain

uniform cross-slope equal to the camber.

- This method has a drawback that the surface drainage will not be proper at the outer half.

Method 2

In this method, the crown is progressively shifted outwards, thus increasing the width of

the inner half of cross-section progressively.

- This method is not usually adopted as a portion of the outer half of the pavement has increasing

value of negative super-elevation.

ii) Rotation of pavement to attain full super-elevation

When the crown of the camber is eliminated, the super-elevation available at this

section is equal to the camber.

There are two methods of rotating the pavement cross-section to attain the full super-

elevation after the elimination of the camber.

(a) By rotating the pavement cross-section about the centre line, depressing the inner edge and

raising the outer edge each by half the total amount of super-elevation.

(b) By rotating the pavement cross-section about the inner edge of the pavement section such

that the outer edge is raised by the full amount of super-elevation.



Method of Elimination of Camber

Following are the method of elimination of the camber and then introduction of the

super-elevation:

(i) By rotating the pavement cross-section about the centre line

By rotating the pavement cross-section about the centre line, depressing the inner edge

and raising the outer edge each by half the total amount of super-elevation, i.e. by ⁄ w.r.t. the

centre.

- In this method, the vertical profile of the centre line remains unchanged; the outer edge is

banked and the inner edge is depressed resulting in an advantage in balancing the earth work.

- The disadvantage of this method is the drainage problem due to depressing the inner edge

below the general level.

- The drainage problem is of greater significance in areas with high rainfall when the subgrade is in

cutting or in level terrain.

(ii) By rotating the pavement cross section about the inner edge of the pavement

section raising both the centre as well as outer edge

By rotating the pavement cross section about the inner edge of the pavement section,

raising both the centre as well as the outer edge of the pavement such that the outer edge is

raised by the full amount of super-elevation, i.e. ‘E’ with respect to inner edge.

- This method is preferable in very flat terrain in high rainfall areas, when the road is no taken on

embankment, in order to avoid drainage problem.

- The entire pavement width and outer shoulder should also be raised w.r.t. inner edge by

additional earth fill, which may alter the vertical alignment of road.

2. Design of Horizontal Alignment

Horizontal Curve

The curve used to change the path of highway in horizontal plane is called horizontal

curve. It may be divided into two groups: (i) Circular & (ii) Transition Curve

i) Circular Curve

It consists of a single or more than one arc of different circles connecting two straight

lines. It may be of:

a) Simple circular curve

Curve consists of single arc of a circle.

b) Compound circular curve

Curve consist two or more arcs of different circles.



ii) Transition Curve

A non-circular curve introduced between a straight and a circular curve is known as

transition curve.

- The radius is infinity at the junction of straight and transition curve while radius ‘R’ at the

junction of transition and circular curve.

- The curvatures of such curves vary from zero at its beginning to a definite value at its

junction with the circular curve.

When a vehicle traverses a horizontal curve, the centrifugal force acts horizontally

outwards through the centre of gravity of the vehicle.

The centrifugal force developed depends on the radius of horizontal curves and the speed of

vehicle negotiation the curve.

Centrifugal force P is given by the equation: P =

where, P = centrifugal force (kg), W = wt. of vehicle (kg), v = speed of vehicle, m/s g = acceleration due to gravity, 9.8 m/s2 R = Radius of the circular curve, m

The centrifugal force acting on a vehicle negotiating a horizontal curve has two effects:

(i) Tendency to overturn the vehicle outwards about the outer wheels (i.e. overturning

effect)

(ii) Tendency to skid the vehicle laterally, outward (i.e. skidding effect)

Extra widening on Horizontal curve

On horizontal curves, especially when they are not of very large radii, it is common to

widen the pavement slightly more than the normal width.

Following are the various reasons for providing the extra widening on horizontal curves:

i) An automobile has a rigid wheel base and only the front wheels can be turned; when the

vehicle takes a turn to negotiate a horizontal curve, the rear wheels do not follow the same

path as that of front wheels. This phenomenon is called off tracking. Due to this, the rear

wheels follow the inner path on the curve as compared to front wheels.

ii) At speed higher than the design speed, when the super-elevation and lateral friction

developed are not fully able to counteract the outward thrust due to centrifugal force and the

rear wheels may take paths on the outside of traced by the front wheels on horizontal curves.

iii) In order to take curved path with larger radius and to have greater visibility at curve, the

drivers have tendency not to follow the central path of the lane, but to use the outer side at

the beginning of a curve.

iv) While two vehicles cross or overtake at horizontal curve there is a psychological tendency to

maintain a greater clearance between the vehicles, than on straights for increase safety.

It has been a practise to provide extra

width of pavement on horizontal curves when

the radius is less than about 300m.



Types of Extra Widening

The extra widening of pavement on horizontal curves is divided into two parts:

i) Mechanical widening

The widening required to account for the off-tracking due to the rigidity of wheel based

is called Mechanical Widening.

where, n = number of traffic lanes R = mean radius of the curve

= length of the curve = mechanical widening

ii) Psychological Widening

The widening required due to various psychological reasons, i.e. clearance, confidence

etc. is called psychological widening.

√

where,

V = design speed, kmph R = radius of horizontal curve, m

Total Extra Widening

√

TRANSITION CURVE

A non-circular curve introduced between a straight and a circular curve is known as

transition curve.

- A transition curve has a radius which decreases from infinity at the tangent point to a designed

radius of the circular curve.

Objectives of providing transition curve

To introduce super-elevation in proportion to the rate of change of curvature.

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

the circular curve.

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

To introduce extra widening of pavement at desirable rate.

To improve the aesthetic appearance of the road.



Types of Transition Curve

(i) Spiral (or clothoid)

Spiral transition curve is a curve, at which radius is inversely proportional to its length.

(ii) Lemniscate

Bernoulli’s lemniscate curve is a curve at which radius varies inversely proportional as its

length of chord.

(iii) Cubic parabola

Cubic parabola curve is a curve, the radius of which varies inversely as its abscissa ‘x’.

Design of Transition Curve

Designing the transition curve means determining of its length. The length of transition

curve is designed to fulfil the following three conditions:

i) Rate of change of Centrifugal acceleration

At the tangent point the centrifugal acceleration (

⁄ ) is zero as the radius ‘R’ is

infinity.

The rate of change of centrifugal acceleration: c =

, [ 0.5 < c < 0.8 ]

Length of transition curve according to rate of change of centrifugal accln: =

ii) Rate of introducing super-elevation

Let, the rate of change of introducing super-elevation be 1 in N;

N = 150 (in plain and rolling) , N = 60 (for hilly area)

Also consider ‘ ’ be the extra width provided at the circular curve; then

Pavement is rotated about inner edge.

=

=

=

(W + ) Pavement is rotated about centre line.

where, = total extra widening =

√

iii) Minimum length by Empirical Formula

a) For plain and rolling terrain; =

b) For mountainous and steep terrain; =

The length of transition curve for the design should be the highest of the three values

mentioned above.

SIGHT DISTANCE

Sight distance is defined as the length of carriageway that is visible to the driver at any

instant from normal height of the driver’s eye above road surface.

Following are the types of sight distances:

1. Stopping Sight Distance (SSD) 2. Overtaking Sight Distance (OSD)



Other sight distances are:

(i) Intermediate Sight Distance (ii) Headlight Sight Distance

1. Stopping Sight Distance (SSD)

The minimum sight distance available along the road to stop a vehicle travelling at

design speed, safely without collision with any other obstruction is called stopping sight

distance.

Factors affecting stopping distance

i) Total reaction time of the driver ii) Speed of vehicle iii) Efficiency of brakes

iv) Frictional resistance between the road and the tyres v) Gradient of the road

i) Total Reaction Time

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

driver to the instant the brakes are effectively applied.

- The stopping distance increases with increase in reaction time of the driver.

- It may be divided into two parts: (a) Perception time (b) Brake reaction time

a. Perception Time

Perception time is the time required for a driver to realise that brakes must be applied.

The perception time varies from driver to driver and also depends upon speed of vehicle,

distance of object and other environmental condition.

b. Brake Reaction Time

It also depends upon various factors, i.e. skill of driver, type of problem and various

environmental factors.

PIEV THEORY

According to this theory, the total reaction time of the driver is split into four parts:

(a) Perception Time: It is the time required to perceive an object or situation.

(b) Intellection Time: It is the time required to understand the situation.

(c) Emotion Time: It is the elapsed time during emotional sensations and disturbance such as

fear, anger or any other emotional sensation.

(d) Volition Time: It is the time taken for final action.

ii) Speed of Vehicle

Higher the speed, higher will be the stopping distance.

iii) Efficiency of Brakes

The braking efficiency is said to be 100% if thee wheels are fully locked preventing them

from rotating on application of the brakes, which will result in 100% skidding.

iv) Frictional resistance between road and tyre

The frictional resistance developed between road and tyres or the skid resistance

depends on the type and condition of the road surface and the tyres.



v) Gradient of the Road

As the stopping sight distance required on descending gradient is higher, it is necessary

to determine the critical value of the SSD for the descending gradient.

2. Overtaking Sight Distance (OSD)

The minimum distance

open to the vision of the driver

of a vehicle intending to

overtake slow vehicle ahead

with safety against the traffic

of opposite direction is known

as overtaking sight distance or

safe passing sight distance.

Factors affecting OSD

(i) Speeds of : (a) Overtaking vehicle (b) Overtaken vehicle (c) Vehicle coming from opposite direction

(ii) Distances between overtaking and overtaken vehicles.

(iii) Skill and reaction time of the driver.

(iv) Rate of acceleration of overtaking vehicle.

(v) Gradient of the road.

Analysis of OSD

Here,

A = position of overtaking vehicle

B = position of overtaken vehicle or slow moving vehicle

C = position of vehicle coming from the opposite direction

= distance travelled by overtaking vehicle A during the reaction time ‘t’ sec. from to .

= distance travelled by vehicle A from to during actual overtaking operation in ‘T’ sec.

= dist. travelled by on-coming vehicle from to during overtaking operation of vehicle A.

Hence, overtaking sight distance is given by; OSD = + +

OSD = t + T + 2 s + v T

Where,

= speed of overtaken vehicle, m/s

t = reaction time of driver = 2 sec



V = speed of overtaking vehicle or design speed

s = spacing of vehicles (= 0.7 + 6, where, ‘6’ is wheel base)

a = acceleration, m/s2

√

3. Design of Vertical Alignment The vertical alignment is the elevation or profile of the centre line of the road.

- The vertical alignment consists of grades and vertical curves.

- It influences the vehicle speed, acceleration, deceleration, stopping distances, sight

distances and comfort in vehicle movement at high speed.

GRADIENT

Gradient is defined as the rate of rise or fall along the length of the road w. r. t. the

horizontal.

- It is expressed as a ratio of 1 in (1 vertical unit to horizontal units).

- It is sometime also expressed as a percentage, n (i.e. n in 100).

Factors affecting gradient

(i) Characteristic of the traffic.

(ii) Design speed

(iii) Physical features of the site (drainage, safety, appearance, access to adjacent property).

(iv) Topography of the country.

Types of Gradient

i) Ruling gradient ii) Limiting gradient iii) Exceptional gradient iv) Minimum gradient

i) Ruling Gradient

Ruling gradient is the maximum gradient within which the designer attempts to design

the vertical profile of a road.

- Gradients up to the ruling gradient are adopted as a normal course in design of vertical

alignment and thus the quantities of cut and fill are balanced.

- Hence ruling gradient is also known as design gradient.

- As per IRC, ruling gradient value is: (a) 1 in 30 (plain & rolling terrain)

(b) 1 in 20 (mountainous terrain)

(c) 1 in 16.7 (steep terrain)

ii) Limiting Gradient

Whenever the topography of a place has steeper gradients, then we provide limiting

gradient which is more than ruling gradient.

- But the length of limiting gradient is limited considering the safety.

- As per IRC, limiting gradient is given as: (a) 1 in 20 (plain and rolling)

(b) 1 in 16.7 (mountainous)

(c) 1 in 14.3 (steep)

Gradient = 1 in tan

= n



iii) Exceptional Gradient

In some cases it may be unavoidable to provide steeper gradient at least for short

stretches and in such cases exceptional gradient may be provided.

- Exceptional gradient should be strictly limited only for short stretches should not exceed about

100m at a stretch.

- As per IRC, exceptional gradient is given as: (a) 1 in 15 (plain and rolling)

(b) 1 in 14.3 (mountainous)

(c) 1 in 12.5 (steep)

iv) Minimum Gradient

It is desirable to have a certain minimum gradient on roads for drainage point of view.

- The minimum gradient would depend upon rainfall run off, type of soil, topography and other

site conditions.

- As per IRC, the minimum gradient of about 1 in 500 may be sufficient to drain water in

concrete drain but for Kucha drain, a slope of 1 in 200 (0.5%) is needed.

Compensation in Gradient on Horizontal Curves At horizontal curves, due to turning angle ‘’ of vehicles, the curve resistance developed

is equal to T (1-cos).

- When there is a horizontal curve in addition to the gradient, there will be increased resistance to

fraction due to both gradient and curve.

- It is necessary that in such cases the total resistance due to grade and curve should not normally

exceed the resistance due to the maximum value of the gradient specified.

- For design purpose, this maximum value may be taken as the ruling gradient and in some special

cases as limiting gradient for the terrain.

- When sharp horizontal curve is to be introduced on road which has already the maximum

permissible gradient, then the gradient should be decreased to compensate for the loss of

tractive effort due to the curve.

- This reduction in gradient at the horizontal curve is called grade compensation. This is calculated

from the relation:

Grade compensation, percent

, subject to a maximum value of 75/R, Where R is the

radius of the circular curve in metre.

VERTICAL CURVE

When two different gradients meet, they are connected by a curve in the vertical plane

known as vertical curve.

Following are objective of vertical curve:

To obtain adequate visibility

To secure comfort to the passenger



Types of Vertical Curves

1. Summit Curve 2. Valley Curve

1. Summit Curve

When the two grades meet at summit and the curve will have the convexity upwards is

called summit curve. It is also called crest curves.

- The deviation angle between the two interacting gradients is equal to the algebraic difference

between them.

case (i) : When a +ve grade meets with a –ve grade.

case (ii) : When a +ve grade meets with another +ve grade.

case (iii) : When an ascending (+ve) grade

meets with zero grade.

case (iv) : When a descending (-ve) grade meets with another –ve grade.

Length of Summit Curve for Stopping Sight Distance (SSD)

There are two cases: (I) When L > SSD (II) When L < SSD

In the diagram,

h1 = height of driver’s eye from road surface

h2 = height of the object lying on the road surface

Since, the curve is square parabola, offset from the line of sight are proportional to the square of

the distance from the point, where the curve is tangential to the line of sight.

h1 = k s12 ------- (i) and h2 = k s2

2 ------- (ii)

where, k = constant of parabola

N = – i 1 – ( – i 2 )

= – ( i 1 – i 2 )



Now,

(

)

√ √

√ √

[√ √ ]

(√ √ )

(√ √ )

We have relation as, L = NR R = ⁄

Putting the value of R in equation (iii), we get;

[ √ √ ]

This is the general equation for length of parabolic curve,

L = length of summit curve, m

S = stopping sight distance (SSD), m

N = deviation angle

(I) When L > SSD

As per IRC, h1 = 1.2 m & h2 = 0.15 m

Putting these values in equation (iv), we get

(II) When L < SSD

The general equation for the length of parabolic summit curve, when it is less than the sight

distance is given by:

[√ √ ]

Putting h1 = 1.2 m & h2 = 0.15 m, we get

Length of Summit Curve for Safe Overtaking Sight Distance (OSD) or Intermediate

Sight Distance (ISD)

There are two cases:

(I) When L > OSD or ISD

The same general equation (iv) is used. By substituting h1 = h2. We get



(II) When L < OSD or ISD

The same general equation (v) is used, by substituting = . We get;

2. Valley Curve

Valley curves or Sag curves are formed in any one of the following cases. In all the cases

the maximum possible deviation angle is obtained when a descending gradient meets with an

ascending gradient.

The most important factors considered in valley curve design are:

(i) Impact free movement of vehicles at design speed or the comfort to the passengers.

(ii) Availability of stopping sight distance under head lights of vehicles for night driving.

Length of Valley Curve

The length of valley curve is designed

based on the two criteria:

a) The length of the transition curve (LS)

for comfort condition

b) The length of valley curve for head light

sight distance

(a) The length of Transition Curve (Ls) for Comfort condition

It is given by,



Now equation (i) becomes;

[

]

⁄

[

]

⁄

Where, N = deviation angle V = speed (m/s) C = allowable rate of change of centrifugal acceleration (taken as 0.6 m/s3)

If V is expressed in kmph, then

⁄

The minimum radius (R metre) of the valley curve for cubic parabola is given by;

(b) The Length of Valley Curve for Head Light Sight Distance

It may be determined for the two conditions: (i) L > SSD (ii) L < SSD

(i) When L > SSD

Consider the height head light is

h1 and the focussed portion of the beam

of light is inclined at an angle upwards.

If the valley curve is assumed to be of

parabolic shape, with equation y = ax2,

where a = ⁄

So,

If = 0.75 m and = 10, then

Where, L = total length of valley curve S = SSD (m) N = deviation angle = i1 + i2

(ii) When L < SSD

Here,

( ⁄ )

When, h1 = 0.75 m & = 10, when L < SSD;



Expression for Stopping Sight Distance (SSD)

Stopping Distance is the sum of Lag Distance and Braking Distance;

………… (i)

here,

= lag distance = distance travelled during total reaction time

= braking dist. = distance travelled by the vehicle after the application of brake

Here, …………. (ii)

Where, = design speed t = reaction time

If ‘F’ be the maximum frictional force developed and be the braking distance then the work

done against frictional force in stopping the vehicle is,

………… (iii) { F = f w} where, w = weight of vehicle f = coefficient of friction

The kinetic energy at the design speed of (m/s) will be,

Equating equation (iii) and (iv), we get;

Substituting the value of lag distance and braking distance in equation (i)

If V is in kmph then,

In case of sloping road of a gradient of , the above equation reduces to;

Here, positive and negative sign with is applicable for ascending and descending gradient

respect.

Set-back Distance on Horizontal Curves In the design of horizontal alignment, the sight distance along the inner side of the

curves should be considered; where there are sight obstructions like buildings, cut slopes, or

trees on the inner side of the curves.

The clearance distance or set back distance required from the centre line of a horizontal

curve to an obstruction on the inner side of the curve to provide adequate sight distance

depends upon the following factors:



(i) Required sight distance, S

(ii) Radius of horizontal curve, R

(iii) Length of the curve, which may be greater or

lesser than S.

(a)

From the figure;

(

)

(

)

The distance from the obstruction to the centre is ⁄ . Therefore the set-back

distance, m required from the centre line is given by;

⁄

In the case of wide roads with two or more lanes, if d is the distance between the

centreline of the road and the centreline of the inside lane in metre, the sight distance is

measured along the middle of the inner side lane and the set-back distance, m’ is given by:

⁄

[

]

(b)

If the sight distance required is greater than the length of curve , then the angle

subtended at the centre is determined with reference to the length of circular curve, and

the set-back distance is worked out in two parts as given below:

⁄

⁄

The clearance of obstruction up to the set-back distance is important when there is cut

slope in the inner side of the horizontal curve.

Solved Example

In a horizontal highway curve of radius 400m and length 200m existed. Compute

the set-back distances required from the centreline on the inner side of the curve

so as to provide for

(a) Stopping sight distance of 90m

(b) Safe overtaking sight distance of 300m

The distance between the centrelines of the road and the inner lane is 1.9m.



Solution:

(a) The stopping sight distance (SSD) of 90 m is less than the circular curve length of 200m.

⁄

Required clearance from the centreline to provide SSD is 90m is 4.4 m.

(b) The overtaking sight distance of 300 m is greater than circular curve of length which is

200m. therefore the required set-back distance is CF = (CG + GF)

S = 300 m, LC = 200 m, R = 400 m, d = 1.9 m

Set back distance m' = CF = CG + GF

⁄

⁄

= 14.4 + 12.4

= 26.8

Minimum set-back distance required from the centre line of the road on the inner side of

the pavement to provide an OSD of 300 m is 27 m.



1) The radius of circular curve is 100 m. The design speed is 50 kmph and the design

coefficient of lateral friction is 0.15.

a. Calculate the super-elevation required if full lateral friction is assumed to develop.

b. Calculate the coefficient of friction needed if no super-elevation is provided.

c. Calculate the equilibrium super-elevation if the pressure on inner and outer wheels

should be equal.

Solution:

Here, R = 100 m V = 50 kmph f = 0.15

(a) Super-elevation, e = ?

we have,

= 4.7 % Ans.

(b) Coefficient of friction, ; when no super-elevation is provided, i.e.

Now, putting values in

(c) Super-elevation, ; for equilibrium condition, i.e.

again, putting values in

2) A two lane road with design speed 80 kmph has horizontal curve of radius 480m. Design

the rate of super-elevation for mixed traffic. By how much should the outer edges of the

pavement be raised w.r.t the centre line, if the pavement is rotated w.r.t. the centre line

and the width of the pavement at the horizontal curve is 7.5 m?

Solution:

For mixed condition, the super-elevation should fully counteract the centrifugal force for

75 % of design speed.

this value is less than 0.07, so adopt e = 0.059

Here, width of pavement (B) = 7.5 m

Now, Raising of outer edge w.r.t. centre,

3) Design the rate of super-elevation for a horizontal highway curve of radius 500m and

speed 100 kmph.

Solution:

For mixed traffic condition;



this value is greater than maximum super-elevation of 0.07, so adopt

Check

For coefficient of lateral friction,

This value is less than 0.15, the design is safe with a super-elevation of 0.07

4) The design speed of a highway is 80 kmph. There is a horizontal curve of radius 200 m

on a certain locality. Calculate the super-elevation needed to maintain this speed. If the

maximum super-elevation of 0.07 in not to be exceeded, calculated the maximum

allowable speed to increase the radius. Safe limit of transverse coefficient of friction is

0.15.

Solution:

The problem may be solved by considering 75% design speed,

Here,

but, Maximum allowable value of

Check for the value of friction developed;

Since this value is greater than maximum allowable safe friction coefficient of 0.15 and

also the radius can’t be increased, the speed has to be restricted.

Maximum allowable speed,

√ √

the speed may be restricted to less than 74 kmph 70 kmph. .

5) Calculate the super-elevation required on a road curve of 240 m radius. The road has

operation dominating in mixed traffic condition. The design speed is 80 kmph. The

coefficient of friction is 0.15. The road is passing through the rolling terrain.

Solution:

R = 240 m V = 80 kmph = 0.15

For mixed traffic condition:

So provide,

Check for friction:

So, provide 7 % super-elevation.



6) Find the total width of pavement on a horizontal curve for a new national highway to be

aligned along a rolling terrain with a ruling minimum radius. Assume necessary data.

Solution:

Assuming following data:

Design speed (V) = 80 kmph (for National Highway in rolling terrain)

Normal pavement width (W) = 7 m

Number of lanes (n) = 2

Length of wheel base ( ) = 6 m

and

We have, Ruling minimum radius (R) =

Total extra widening ( ) = mechanical widening ( ) + psychological widening ( )

√

√

Total extra widening = 7 + 0.72 = 7.72 m .

7) Calculate the length of transition curve and shift for the following data:

Design speed : 70 kmph

Radius of circular curve : 250 m

Allowable rate of introduction of super-elevation : 0.07

pavement rotated about centreline : 1 in 140

Pavement width including extra widening : 7.5 m

Solution:

(a) Length of transition curve as per allowable rate of change of centrifugal acceleration (C);

It lies between 0.5 & 0.8, (hence OK)

(b) by allowable rate of introduction of super-elevation;

So, adopt

Check for frictional resistance

The value of is safe for design speed 70 kmph.

Here, width of pavement (B) = 7.5 m

1 in N = 1 in 140 } (given)

Total raise of outer edge w.r.t. centre line;



(c) By empirical formula;

Adopt highest value of three;

Length of transition curve ( ) = 53.65 m 54 m .

8) A National Highway passing through rolling terrain in heavy rain fall area has a horizontal

curve of radius 500m. Design the length of transition curve assuming suitable data.

Solution:

Assume; V= 80 kmph , ⁄

⁄ , W = 7 m

Given; R = 500 m

(a) Length of transition curve as per allowable rate of change of centrifugal acceleration;

It lies between 0.5 & 0.8, (hence OK)

(b) by allowable rate of introduction of super-elevation;

Extra-widening; (Assuming, n = 2 and = 6 m)

√

√

Total width of pavement, B = 7 + 0.45 = 7.45 m

= (rotating about the inner edge)

= 0.057 7.45 150 = 63.7 m

(c) By empirical formula;

Adopt highest value of three;

Length of transition curve ( ) = 63.70 m 64 m .

9) A clothoid is to be fitted in between the circular section and a straight section of

highway. If the design speed on the highway is 85 kmph and radius of the curve of the

circular section is 225m. Determine the length of clothoid for comfort condition and for

introducing maximum super-elevation @ 1 in 150. The width of pavement at the straight

section is 7m and the length of wheel base of the design vehicle is 6.1m.

Solution:

Here; V = 85 kmph R = 225 m W = 7 m = 6.1 m ⁄ = 1 in 150



Step 1 : To check super-elevation

Step 2 : To check friction coefficient

Step 3 : Allowable / comfort velocity

√ √

Now, for the comfort condition;

For e = 0.07

& f = 0.15 } V = 79.29 kmph

Step 4 : Rate of change of centrifugal acceleration

⁄

Step 5 : Rate of introducing super-elevation

√

√

Step 6 : By empirical formula

Provide higher value of So, .

10) Calculate the safe stopping sight distance for design speed of 50 kmph for:

(a) Two-way traffic on a two lane road (b) Two-way traffic in a single lane road

Assume coefficient of friction as 0.37 and reaction time of driver as 2.5 sec.

Solution:

Stopping distance = lag distance + braking distance

(a) Stopping sight distance when there are two lanes = stopping distance = 61.35 m

(b) Stopping sight distance for two way traffic with single lane = 2 SD

= 2 61.35 = 122.7 m

11) Calculate the minimum sight distance required to avoid head on collision with a car

approaching from the opposite direction if both the cars are speeding at 60 kmph. Use a

total perception and brake reaction time of 2 second, coefficient of friction and

brake efficiency . The section of the road under consideration has a

grade of 10%.



Solution:

V = 60 kmph, t = 2 sec, f = 0.40

= 50 % = 0.50, grade ( ) = 10% = 0.10

Stopping sight distance for ascending car,

Stopping sight distance for descending car,

Required minimum SSD = = 90.05 + 127.85 = 217. 90 m.

12) Calculate the values of:

(a) Head light sight distance

(b) Intermediate sight distance for a highway

with a design speed of 65 kmph

Assume suitably

all the data required.

Solution:

V = 65 kmph, Assume, t = 2.5 sec

f = 0.36

(a) Head light sight distance = SSD

(b) Intermediate sight distance = 2 SSD

= 2 91.38 = 182.76 m

13) Calculate the safe stopping sight distance for a vehicle in a descending section of road,

moving at a speed of 60 kmph.

(a) Two way traffic in two lane road (b) Two way traffic in single lane road

Given, t = 1 sec, = 0.4, grade = 5 %

Solution:

Stopping distance for descending section;

(a) Minimum stopping sight distance for two lane road = SD = 57.17 m.

(b) Minimum stopping sight distance for single lane road = 2 SD

= 2 57.17 = 144.34 m.

14) A vehicle moving at a speed of 90 kmph decided to overtake another slow moving

vehicle. Calculate safe overtaking sight distance. Consider:

(a) Two lane road with two way traffic (b) Two lane road with one way traffic

Assume all data suitably. Acceleration = 2.5 km/hr/sec

Solution:

V = 90 kmph, t = 2.5 sec

Speed of overtaken vehicle ( ) = V – 16 = 90 – 16 = 74 kmph



Now, Distance ( ) = 0.278 t = 0.278 74 2.5 = 51.43 m

Spacing between the vehicles (s) = 0.69 0.278 + 6.1

= 0.69 0.278 74 + 6.1 = 20.29 m

Overtaking time (T)

√

√

Distance ( ) = 0.278 T + 2 s = 0.278 74 10.81 + 2 20.29 = 262.96 m

Distance ( ) = 0.278 V T = 0.278 90 10.81 = 270.47 m

(a) OSD =

= 51.43 + 262.96 + 270.47 = 584.86 m.

(b) OSD =

= 51.43 + 262.96 = 314.39 m.

15) The speed of overtaking and overtaken vehicles is 60 kmph and 30 kmph respectively

on a two way traffic road. If the acceleration of overtaking vehicle is 3.6 kmph/sec.

(a) Calculate the safe overtaking sight distance

(b) Determine the minimum length of overtaking zone ( 3 to 5 times of OSD )

Solution:

Design speed (V) = 60 kmph

Speed of overtaken vehicle ( ) = 30 kmph

Acceleration of overtaking vehicle (a) = 3.6 km/hr/sec

Let, Reaction time (t) = 2.5 sec

Distance travelled by overtaking vehicle ( ) = 0.278 .t = 0.278 30 2.5 = 20.85 m

Minimum distance between two vehicles (s)

= 0.69 0.278 + 6.1 ( length of wheel base = 6.1 m)

= 0.69 0.278 30 + 6.1 = 11.85 m

Overtaking time (T)

√

√

Distance travelled by overtaking vehicle during actual operation of overtaking,

= 0.278 T + 2 s = 0.278 30 6.88 + 2 11.85 = 81.08 m

Distance ( ) = 0.278 V T = 0.278 60 6.88 = 114.76 m

(a) Safe overtaking sight distance, OSD =

= 20.85 + 81.08 + 114.76 = 216.69 m.

(b) Minimum length of overtaking zone = 4 OSD ( 3 – 5 times of OSD )

= 4 216.69 = 866.76 m.

16) A vertical summit curve is formed at the intersection of two gradients, +3.0 and – 5.0 %.

Design the length of summit curve to provide a stopping sight distance for a design

speed of 80 kmph. Assume necessary data.

Solution:

N =

= 0.03 – ( – 0.05 ) = 0.08



Let, t = 2.5 sec

= 0.35 for V = 80 kmph

Assuming L > SSD,

Length of summit curve = 298 m.

17) An ascending gradient of 1 in 100 meets a descending gradient of 1 in 120. A summit

curve is to be designed for a speed of 80 kmph so as to have an overtaking sight

distance of 470 m.

Solution:

N =

Here, OSD = 470 m

If L > OSD:

But, L OSD

So, Let L < OSD:

⁄

L < OSD (assumption is OK)

Length of Summit Curve = 417 m.

18) A valley curve is formed by a descending gradient of 1 in 150 which meets an ascending

gradient of 1 in 40. Design the total length of valley curve if the design speed is 80 kmph

so as to fulfil both comfort condition and head light sight distance for night driving, after

calculating SSD required.

Solution:

V = 80 kmph

(a) Comfort condition:

⁄

(

)

⁄



(b) Headlight sight distance condition:

Neglecting ascending & descending gradient at valley curve

& assuming t = 2.5 sec, f = 0.35

If L > SSD,

But, L SSD,

So, Let; L < SSD, then

⁄

= 122.61 m < SSD (assumption is correct)

Length of valley curve on headlight sight distance is higher than that on comfort condition

Length of valley curve = 122.61 m 123 m.



[5] HILL ROADS

A hill road is defined as the one, which passes through with a cross slope of 25% or more

i.e. mountainous or steep.

- As per NRS the cross slope may be classified as:

Type of Terrain 1. Level or plain 2. Rolling 3. Mountainous 4. Steep

Cross Slope (%) 0 – 10 10 – 25 25 – 60 > 60

Special consideration in the Aligning of Hill roads Following points to be considered while aligning the hill roads:

i) Temperature The temperature of air varies inversely with altitude. The temperature drop being about

0.50C per 100m of rise.

- Similarly, the amount of heat received by hill slopes varies enormously with their orientation

in relation to the exposure to sun.

ii) Rainfall The amount of rainfall in hilly region is inversely proportional to the altitude.

- In hilly regions, wind often flows along the valley and gorges, as consequence of which the

rainfall in the valley is substantially higher than on high-lands and water-sheds.

- Also, maximum rainfall occurs in few months only. So these all uneven situation create the

problem in construction and maintenance of the road.

iii) Atmospheric pressure and Winds

Atmospheric pressure is inversely proportional to altitude. At high altitudes, the velocity

of wind is frequently coming at 25 – 30 m/s.

- The change in character of wind is due to appreciable difference of atmospheric pressure in

valleys and on mountain passes.

iv) Geological condition

The tendency of sedimentary rocks is to slip under the influence of force parallel to the

layer.

- The degree of stability of hill slopes depends upon the type of rock, the degree of strata

inclination or dip, the occurrence of clay seem, the hardness of rock and presence of ground

water.

- The instability of road may be due to ground water, landslides and unstable folds.

v) Route location

The approach to the location of hill road alignment varies for the sections along the

valley bottom and along the mountain pass.

The first is called ‘river route’ and second is called ‘ridge route’.



a) River route

The location of a route along the river valley is known as river route. River route

is frequently used in hill road due to comparatively gentle gradient.

- It is advantageous that availability of water and other construction material in vicinity.

- However, a river route may involve numerous horizontal curves, construction of large

bridges over tributaries and on stretches along steeply sloping hill sides.

- It may also be necessary to construct special structures on hill side for the safe of road

against landslides.

b) Ridge route

A ridge route is characterised by very steep gradient, numerous sharp curves

including hair pin bends and the expensive rock works.

- The road usually follows the top section of the hill system and crosses successively

mountain pass.

- Geologically stable and comparatively mild slope sections are selected for the artificial

development of the route.

Hill Road Design

i) Sight Distance

The stopping sight distance is calculated from the relation;

where, V = design speed of vehicle, kmph t = reaction time f = coefficient of friction

SSD (As per NRS 2027)

Speed (kmph): 20 30 40 50 60 80 100 120

SSD (m): 20 30 45 65 85 110 145 250

The overtaking sight distance is calculated from the relation;

where, V = speed of overtaking vehicle, kmph = speed of overtaken vehicle = ( V – 16 ) kmph S = spacing of moving vehicle = ( 0.2 + 6 ) m

√

A = acceleration in kmph/sec

ii) Super-elevation

The super-elevation to be provided at horizontal curves of hill road is calculated from;

As per IRC, the super-elevation must not be greater than 7 % in hill roads.

iii) Radius of Horizontal curves

The radius of horizontal curves in hill roads, (minimum) is calculated by;

Where, R = radius of curve, m V = design speed, kmph

e = super-elevation (m/m) = coefficient of friction (0.15)



iv) Widening of Curves

Extra width of carriage way ( ) at horizontal curve is calculated from the relation;

√ Where, n = number of lanes

v) Set back distance

As it is not possible to provide visibility corresponding to overtaking sight distance all

along the hill road, the alignment is made so as to provide at least the safe stopping sight

distance.

vi) Transition curves

The length of transition curve is calculated form the relation,

Here,

vii) Gradients

The gradient for the given section of the road is normally selected maximum one in

order to reduce the earthwork and route length.

- The gradient of road decreased as height above MSL increases.

- The values of ruling and limiting gradient in mountainous and steep terrain over 3000 m

height above MSL are 5 % and 6% respectively.

viii) Camber or Cross fall

The recommended values of camber for hill roads (as per IRC) are given below;

S.N. Type of Surface Camber (%)

1. 2. 3. 4.

Subgrade, earthen road and shoulders Gravel and WBM surface Bituminous surfacing High type bituminous surface

3 – 4 2.5 – 3

2.5 2

ix) Hair pin bends

In aligning a hill road, it becomes necessary to attain height at a particular location

without substantial covering of horizontal distance. In such cases, hair pin bend is provided.

Design of Hair Pin Bend Within the limits of the available turning angle, it is often very difficult and sometimes

even impossible to lay out curves following normal geometric standards of design. In such

conditions, the curve provided on hill side having the minimum slope and maximum stability,

is called hair pin bends.

- It must be safe from view point of landslides and ground water.

- It may reduce construction problems and expensive protective works.

Design criteria for hair pin bends

The following design criteria are adopted for planning hair pin bends:

a) The straight length between two successive hair pin bends should be minimal of 60m

excluding the length of circular and transition curve.



b) Minimum design speed = 20 kmph

c) Minimum radius of inner curve = 14 m

d) Minimum length of transition = 15 m

e) Super-elevation in circular portion of the curve = 1 in 10

f) Minimum width of carriageway at the apex of curves should be 11.5 m and 9 m for two-

lane and one lane respectively.

g) The maximum and minimum gradients should be 1 in 40 and 1 in 200 respectively at the

curve.

h) For good visibility at the hair pin bend, the island portion shall be cleared off all the trees

etc.

Expression for Hair Pin Bends

Fig: Hair Pin Bend

Here, T = tangent length of reverse curve R = radius of main curve

= deflection angle = length of the reverse curve C = length of the main curve m = transition length between reverse and circular curve

= central angle at the centre of main curve r = radius of reverse curve

Tangent length of reverse curve = ⁄

⁄

⁄

⁄

Equating (i) and (ii)

⁄

⁄

⁄

⁄ ⁄

⁄

⁄ ⁄ ⁄

⁄ ⁄ ⁄

⁄ ⁄ ⁄

⁄ ⁄

This is a quadratic equation of ⁄ .

⁄ √

√



Neglecting negative sign;

⁄ √

After knowing the value of ,

Deflection angle at main curve,

Length of reverse curve,

Length of main curve, C

Total Length of Hair Pin Bend (S) = 2 ( + m ) + C

Design and Construction of Hill Roads i) Rock Cutting

If the rock strata slope downward into the hill-side, the rock is permitted to overhang

the road forming a half tunnel. Blasting is done either from face or from one or both sides.

- If the strata are inclined towards the hill slope, cutting is continued until the inner slope is

at a safe angle to prevent slipping. In such case, blasting and cutting is commenced from

top.

ii) Precipice Work

Where the time available does not allow for blasting and tunnel work, cliff galleries and

cradles are resorted for the negotiation of cliffs and precipices.

- These are suitable only for light vehicles or foot traffic and considered only for short term

use and not as a permanent roadway for regular traffic.

iii) Retaining Walls

Retaining walls are most important structures in hill road construction to provide

adequate stability to the roadway and to the slope.

- Retaining walls are constructed on the valley side of the roadway and also on the cut hill

side to prevent land slide towards the roadway.

- The rear face of wall is vertical and filled with boulders and stones to improve drainage

and to resist earth pressure for half the height.

iv) Revetment Walls

The embankment slopes are normally protected with rough stone pitching about 30 cm

thickness in order to avoid erosion due to flow of water.

- If the stopping length is too long, it is preferable to construct a toe wall to support the

embankment.

v) Pavement type

Because of the high intensity of rainfall, generally throughout the year in the hill regions,

an impermeable type of pavement proves more effective, though the initial cost may be

high.



- The bituminous pavements are preferred on hill road.

- Cement concrete roads are not considered suitable because of its high initial cost and

delay in construction.

Construction Problems in Hill Roads Construction of roads in hills and mountain is more complex task than in plain, due to

the following reasons:

(i) A hilly or mountain area is characterised by a highly broken relief with widely differing

increase in length of road.

(ii) The geological condition of hill varies from place to place within a short section, which may

create problem for foundation of road structures.

(iii) Hill cross slopes which are stable before the construction may turn into unstable after the

construction due to removal of vegetation or by movement of construction equipment.

(iv) Variation in hydro-geological conditions, (ground water condition) from place to place, may

result in unexpected damage after and during construction i.e. landslides, slip etc.

(v) Highly broken relief requires the various types of road structures such as aqueducts,

retaining walls, tunnels etc., which may increase 50 – 60 % of total construction cost.

(vi) Presence of steep ground cross slope needs careful arrangement of erosion protection

work.

(vii) Variation in climatic conditions such as temperature, pressure, velocity of wind etc. should

be considered in the design and construction period.

(viii) Special safety precaution should be taken for earthwork erection of retaining structures

and bridge construction.

Maintenance Problems in Hill Roads

i) Maintenance of drainage structures

Catch water drains, side drains, catch pits and culverts are periodically cleared off of all

blockages to prevent overflowing during rains.

- Planting of tress on the upper slopes in order to reduce the scouring action of unstable

ground due to rain.

ii) Snow clearance

Because of snow accumulation, most of hill roads at very high altitudes are closed for

traffic in winter.

- The first problem in snow clearance is to correctly locate the position of the road and

other structures under snow cover. It is overcome by erecting snow markers.

- Then snow clearance is done by machines; but care must be when using them on black top

surfaces not to damage them.

iii) Control of avalanches

On some sections, special protective structures called galleries are constructed above

the roads which permit the snow mass to slide over the gallery roof without inducing

impact loads.



iv) Prevention of landslides

Landslides and slips are most important problem in the maintenance of hill roads. To

tackle this, the engineer has to study the causes, correction and remedial measures.

- The term landslide denotes downward and outward movement of slope forming materials

composed of natural rocks, soils, artificial fills or combination of them.

v) Slide movements

Where shear stresses exceed the shear strength of the soil, movement occurs.

Following are some causes of increased stress condition:

(a) Increase in water content

(b) External load due to traffic, accumulation of snow

(c) Undermining caused by excavation or erosion

(d) Shocks and vibrations cause by earthquakes or blasting

Drainage in Hill Roads

1) Drainage of water from hill slopes

Surface water flowing form the hill slope towards the roadway is one of the main

problems in drainage of hill roads.

- It is desirable that the water from the hill side is not allowed to flow into the side drains

due to the problems maintaining the side drains intended for water from roadway.

- In order to intercept and divert the water form hill slope catch water drains are provided

and then it is diverted by side drain.

2) Road-side drains

Side drain is provided only on the hill side of the roads and not on the both sides. Due to

limitation of in the formation width, the side drains are constructed to such a shape that at

emergency the vehicles could utilize the space for crossing at low speed or for parking.



3) Cross drainage

As far as possible, cross drainage should be taken under the road and at right angle to it.

- At the head of small cross drains catch pits must be provided to collect the stones and

rubbish and to prevent scour.

- In hill roads where rainfall is heavy, it is recommended that culverts should be provided

every 60 to 90 m, to facilitate drainage of water cross the roads.

4) Sub-surface drainage

The seepage flow of water on hill roads is one of the major problems during and after

the monsoons.

- The seepage flow causes problems of slope stability as well as weakening of the road bed

and the pavement.

- The seepage flow is controlled by suitable sub-surface drainage system i.e. by longitudinal

pipe drain, by controlling of capillary rise, by lowering the water table.

Structures in Hill Roads On the basis of function of structures, these are classified into:

1. Retaining structures 2. Drainage structures

1) Retaining structures

A retaining structure is usually a wall constructed for the purpose of retaining a vertical

or nearly vertical earth bank which in turn supports vertical loads.

- It provides adequate stability to roadway and to the slope.

- It is constructed on the valley side of the roadway and also on the cut hill side to prevent

slide towards the roadway.

- They are also provided to retain the earth mass for elevated and depressed roads.

Design

The design of retaining wall as a thumb rule provided by Hager and Bonney is

done by following ways:

(i) A section of 0.5 H with a minimum width of 0.45 – 0.60 at top.

(ii) The rear side of retaining wall should be vertical while front batter of 1 in 4.

(iii) The height > 6 , the base width of (0.4 H + 0.3) to (0.5 H + 0.6) is adopted with

a top width of 0.75 .

Types

A. Based on material used B. Based on the location C. Based on structural scheme

i. Dry stone masonry ii. Stone filled gabion crates

iii. Stone masonry with c/m iv. Composite retaining wall v. RCC retaining wall

i. Hill or valley side ii. Toe wall

iii. Cut off wall iv. Revetment wall

i. Gravity wall ii. Semi-gravity wall

iii. Cantilever wall iv. Buttressed wall



2) Drainage structures

Drainage is one of the main problems during construction as well as operation of roads.

Hill road construction is said to be the battle against water and this battle indeed is a very

difficult one.

- Surface water flowing from the hill slope towards the road way is one of the main

problems in drainage of hill roads.

- Water intercepted by the catch drain is diverted by sloping drains and carried across the

road by means of culvert.

- If catch drain is not properly constructed and maintained then road way or side drain may

damage.

- Lining may have to be done to prevent scouring.

- Energy dissipating structures like chutes may have to be provided for road side drain.

Passing Lane in Hill Roads

The construction of hill road is not only costly but also tedious work due to abrupt

change in level, geological conditions and limited funds.

- Sometimes it is very difficult to cut the hard rocks, while sometimes very tedious to make

stable flow ground.

- So the width of hill roads is not uniformly throughout.

- Minimum width of hill roads is fixed based on the geological conditions, traffic volume,

method of construction, availability of fund and locality.

- At certain interval some extra space is provided to pass the traffic coming from opposite

direction or to overtake. This type of arrangement is called passing lane in hill roads.



[6] HIGHWAY DRAINAGE

Definition Highway drainage is the process of removing and controlling excess surface and subsoil

water within the right of way. This includes interception and diversion of water from the

road surface and subgrade.

Importance of Highway Drainage Highway drainage is important because of the following reasons:

i) Excess moisture in soil subgrade causes considerable lowering of its stability.

ii) Increase in moisture causes reduction in strength of many pavement materials like stabilised

soil and water bound macadam.

iii) In some clayey soils variation in moisture content causes considerable variation in volume of

subgrade. This sometimes contributes to pavement failure.

iv) One of the most important causes of pavement failure by the formation of waves and

corrugations in flexible pavements is due to poor drainage.

v) Excess water on shoulders and pavement edge causes considerable damage.

vi) Excess moisture causes increase in weight and thus increase in stress and simultaneous

reduction in strength of the soil mass.

vii) Erosion of soil from top of un-surfaced roads and slopes of embankment, cut and hill side is

also due to surface water.

viii) The main cause of failures in rigid pavements by mud pumping is due to the presence of

water in fine subgrade soil.

Requirements of Highway drainage system (i) The surface water from the carriageway and shoulder should effectively be drained off

without allowing it to percolate to subgrade.

(ii) The surface water from the adjoining land should be prevented from entering the roadway.

(iii) The side drain should have sufficient capacity and longitudinal slope to carry away all the

surface water collected.

(iv) Flow of surface water across the road and shoulders and along slopes should not cause

formation of cross ruts or erosion.

(v) Seepage and other sources of underground water should be drained off by the subsurface

drainage system.

(vi) Highest level of GWT should be kept well below the level of subgrade, preferably by at least

1.2 .

Classification of Highway drainage system Highway drainage system can be classified as:

1) Surface drainage system

(a) Longitudinal drainage system: Road side drain, Intermediate drain, Catch drain

(b) Transverse drainage system: Culverts, Causeway, Aqueduct, Inverted siphon

(c) Energy dissipating measures: Drain lining, Ditch decks, Drop or fall structures



2) Subsurface drainage system

(a) Control of seepage flow

(b) Control of capillary rise / vapour transfer

(c) Lowering of water table

SURFACE DRAINAGE The surface of 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.

Design of Surface drainage system

( ) Hydrologic Analysis ( ) Hydraulic Analysis

i) Hydrologic analysis

The main objective of hydrologic analysis is to estimate the maximum quantity of water

expected to reach the element of the drainage system under consideration.

- A portion of the precipitation during the rainfall infiltrates into the ground as ground

water and a small portion gets evaporated.

- The remaining portion of water which flows over the surface is called run-off.

- Various factors affecting the run-off are:

Rate of rainfall Type of soil and moisture condition

Topography of the area Type of ground cover, like vegetation, etc.

- The peak run-off water for highway drainage is widely computed by:

Where, Q = run-off (m3/s) C = run-off coefficient

I = intensity of rainfall (mm/hr.) A = drainage area (ha)

Design Steps

(i) Find the frequency or return period

(ii) Run-off coefficient and drainage area

(iii) Time of flow for the estimated longitudinal drain to the nearest cross drainage or water

course.

(iv) Inlet flow to the drainage and flow along the drain (time of concentration).

(v) Total area of drainage (ha), rainfall intensity (mm/hr.)

(vi) Run-off quantity (Q) = ⁄

(vii) Cross-sectional area of flow of the drain (A) = ⁄ (where, V is the allowable velocity in

the drain)

(viii) The required depth of flow in the drain is calculated for a convenient width and side

slope of the drain.

(ix) Required longitudinal slope (S) of the drain is calculated by using Manning’s formula

adopting suitable value of roughness coefficient.

ii) Hydraulic analysis

Once the design run-off is determined, the side drains and partially filled culverts are

designed based on the principles of flow through open channels.



- If is the Quantity of surface water ( ⁄ ) to be removed by a side drain and is the

allowable velocity of flow ( ) on the side drain, the area of x-section of the channel

( ) is given by the relation: .

- By using the Manning’s formula, the longitudinal slope or velocity of flow is given by;

Where, V= avg. velocity ( ) n = Manning’s roughness coefficient R = hydraulic radius S = longitudinal slope of channel

- Determine wetted perimeter from; ⁄

- Determine the dimensions i.e. width (b) and depth (d), from:

i.e.

√

( for trapezoidal drain)

- If the depth of flow (d) >

⁄ (critical depth), then it’s OK.

SUB-SURFACE DRAINAGE Changes 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. The removal of water located below the ground level is known as sub-

surface drainage system.

Following methods are normally used for surface drainage system:

i) 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 at least 1 –

1.2 m below the subgrade.

- In places where water table is high, the best remedy is to take the road formation on

embankment of height not less than 1.0 – 1.2 m.

- When the formation is to be at or below the general level, it would be necessary to lower

the water table.

- If the soil is relatively permeable, it may be possible to lower the high water table by merely

construction of longitudinal drainage trenches with drain pipe and filter sand.

ii) Control of Seepage flow

When the general ground as well as the impervious strata below are sloping, seepage

flow is likely to exist.

- If the seepage zone is at depth less than 0.6 – 0.9 m from the subgrade level, longitudinal

pipe drain in trench filled with filter material and clay seal may be constructed to intercept

the seepage flow.



iii) Control of Capillary rise

The capillary rise may be checked either by a capillary cut-off of any one of the following

two types:

(a) A layer of granular material of suitable thickness is provided during the construction of

embankment between the subgrade and the highest level of sub-surface water table.

(b) Another method of providing capillary cut-off is by inserting an impermeable or a

bituminous layer in the place of granular blanket.

Design of Sub-surface Drainage System

The size and spacing of sub-surface drainage system would depend on the

quantity of water to drain off, the type of soil and type of the drains.

- Proper filter material should be used for back filling the drainage trenches and also for use

in all sub-surface drainage system.

Design of filter material

The filter material used in sub-surface drains should be designed to have sufficient

permeability offering negligible resistance to the flow. The procedure for design of filter is

briefly discussed here;

(i) On a grain size distribution chart (% passing vs. particles size on log scale) plot the grain size

distribution curve for the foundation soil.

(ii) Find the value of size of foundation material and plot a point of particle size of

foundation to represent the lower limit of size of filter. This is to fulfil the permeability

condition given by:

(iii) To fulfil the condition to prevent piping

Hence plot a point to represent the upper limits of size of filter given by of

foundation.

(iv) The size of perforation in the drain pipe = (filter) and no definite procedure for

determining the number of perforation per unit length of pipe.



Erosion control and Energy dissipating structure

1) Erosion control Water emerging out of culverts and other cross drainage structures generally will have

the velocity higher than the non-scouring velocity for the soil around it.

- Similarly, in many cases, the bed slope of road side drains and intercepting drains may be so

high that the velocity of water flowing among them may erode its bed and side.

Following methods are used for erosion control:

i) Lining of drain

If the mean velocity exceeds the permissible for the particular kind of soil the road drain

should be protected against scouring.

- The slope of drain is lined with turf and bottom is covered by cobbles and gravels of the

desired size.

- Grass linings are valuable where grass can be supported.

- For higher velocity, stone masonry riprap lining or brick masonry, precast concrete block

throughout the perimeter and length of drain is appropriate.

ii) Vegetation

Vegetation is a process of application of grass on the top surface of exposed soil. Soil

erosion control is improved by allowing vegetation to grow in the fill slopes, side borrow

and shoulder portion of roadways.

- Bio-engineering is other alternative which has proved more effective with sustainable

development with age.

- The use of bio-engineering is environment friendly is not only in erosion control but also in

slope stabilisation.

iii) Slope pitching, lining and protection walls

Due to various reasons slope of cut and fill should be provided higher than the angle of

repose for the soil.

- In such cases, various types of slope protection works like stone, plain concrete, RCC,

timber, etc. may be provided against grass growing.

- Erosion control may be controlled by proper water shed management.

2) Energy dissipating structures When flowing out along and out of drainage structure is contracted to reduce the size;

the velocity of flow increases. As a result of increase in the velocity of flow, the kinetic

energy of water increases which may cause erosion of soil ahead. So the use of energy

dissipating structure is to dissipate the energy of flowing water.

Following are some energy dissipating structures:

i) Road rapid

Rapids are provided on short length as inlet and outlet drain adjacent to some cross

drainage structures.

- It is also provided at the end section of catch or intercepting drains.

- A rapid consists of inlet, main conduit, stilling basin and outlets.



ii) Ditch deck

In case of large rapid slope, the flowing water has great energy having capacity to erode

the bed and side slope of drain.

- The energy of flowing water can be reduced by providing falls at certain intervals.

iii) Fall or drop structures

In the design of road drainage system in hill road it is often necessary to provide drop

structures.

- Such structures are to be provided frequently in hill roads where the bed slopes of existing

drainage ways is very high.

- These structures may be provided both u/s and d/s of the cross drainage structures.

Cross drainage structures used in highway Following are the main types of x-drainage structures used in highway:

i) Causeways

When the flow of water is not only temporary but also about or slightly below the level

of road, then the structure is called causeway.

- A causeway does not restrict the waterway and is constructed perpendicular to the

direction of flow.

ii) Inverted siphon

Inverted siphon is provided in the case, if the invert level of conduit across the road is

lowered to the desired level and both inlet and outlets are provided to receive flow and

discharge to the d/s respectively.

iii) Aqueduct

If the road is in cutting exceeding and the water either of natural drainage or

irrigation canal has to be drained or taken to irrigate the land, aqueduct is the best

structure.

iv) Culvert

A culvert is a close conduit (span < 6 m) placed under the embankment to carry water

across the roadway. It may be of following types:

(a) Slab culvert (b) Box culvert (c) Arch culvert (d) Pipe culvert - Culvert is more hydraulically efficient than bridges.



v) Scupper

A scupper is a cheap type of culvert having

0.9 – 1 m wide, made of coursed rubble dry

masonry abutments. Retaining walls are

provided on both ends of the scupper.

A longitudinal channel with a trapezoidal x-section is to be constructed in a cut section.

The longitudinal slope of 1 in 2500 and cross slope of ( ). The soil is clay, with

Manning’s roughness coefficient of 0.024. The maximum allowable velocity is 0.6 m/s.

Design the channel for discharge of .

Solution:

Here, Longitudinal slope (s) = 1 / 2500

Cross slope or side slope (1: r) = 1: 2

V = 0.6 m/s Q = 3 m3/s n = 0.024

b = ?, d = ?

We have,

⁄

⁄

⁄ ( ⁄ )

⁄

Now, Q = AV

Again,

Also,

√ √

Putting the value of b in equation (i), we get;

Solving this equation, we get;

d = 0.8055 0.81 m

b = 8.1967 – 4.47 0.81 = 4.60 m

Now,



[7] HIGHWAY MATERIALS

Classification of Materials

1. Binding materials The materials used to unite or bind two or more materials during the construction

process are called binding materials. These are divided into three groups:

(i) Stone dust: Produces semi rigid or semi flexible bond between the mineral materials.

(ii) Inorganic materials: Produces rigid bond between the mineral materials. E.g. cement, lime, etc.

(iii) Organic materials: Produces thin film or layer which is flexible and reversible in nature. E.g. bitumen

2. Mineral materials Mineral materials used for the construction of highway are soil, sand (fine aggregate),

stone chips, gravel, stone dust, blast furnace slag, brick etc.

- Soils are extensively used for the embankment construction while stone aggregates are used

in pavement construction as well as filter materials in the backfill of retaining walls.

3. Other materials Other materials used in highway construction are timber, reinforcing steel, stone, brick

boulders, cobbles, etc.

Desirable properties or Road Aggregates Following are the desirable properties of road aggregates:

i) 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 used in top layers of the pavements, particularly in wearing course

should withstand high wear and tear to resist the crushing strength.

ii) Hardness

The aggregates used in the surface course are subjected to constant rubbing or abrasion

due to moving traffic.

- They should be hard enough to resist the wear due to abrasive action of traffic.

iii) Toughness

The aggregates in the pavements are also subjected to impact due to moving wheel

loads.

- The magnitude of impact would increase with the roughness of the road surface, the speed

of the vehicle and other vehicular characteristics.

- The resistance to impact or toughness is hence another desirable property of aggregates.



iv) Durability

The stone used in pavement construction should be durable and should resist

disintegration due to action of weather.

- The property of the stones to withstand the adverse action of weather may be called

soundness.

- The road stones used in the construction should be sound enough to withstand the

weathering action.

v) Shape of aggregates

The flaky and elongated particles will have less strength and durability then cubical,

angular or rounded particles of same stone.

- Hence, too much flaky or elongated aggregate should be avoided as far as possible.

- Rounded aggregates may be preferred in cement concrete mix due to low specific surface

area and better workability for the same proportion of cement paste and same w/c ratio.

- Angular aggregates are preferred in granular base course, WBM and bituminous

construction, due to their better interlocking properties.

vi) Adhesion with Bitumen

The aggregate used in bituminous pavements should have less affinity with water when

composed with bituminous materials; otherwise the bituminous coating on the aggregate

will be stripped off in presence of water.

Test for Road Aggregates In order to decide the suitability of the road stones for use in construction, the following

tests are carried out:

1. Crushing strength test (for strength) 2. Abrasion test (for hardness) 3. Impact test (for toughness)

4. Soundness test (for durability) 5. Shape test 6. Sp. Gravity & Water absorption test

1. Crushing strength test

The strength of coarse aggregate may be assessed by aggregate crushing test. The

aggregate crushing value provides a relative measure of resistance to crushing under

gradually applied compressive load.

Equipment

(a) Steel Cylinder:

- 15.2 cm internal diameter with base plate and plunger - Height of cylinder vary from 13 to 14 cm - Wall thickness of 1.6 cm

(b) Cylindrical measure: (c) Steel tamping rod:

Internal diameter of 11.5 cm & height 18 cm Length of the rod 45 – 60 cm & diameter 1.6 cm

(d) Compressive testing machine



Procedure

(i) Take and dry the aggregate passing from 12.5 mm sieve and retained on 10 mm.

(ii) Fill the sample in cylindrical measure in 3 layers by tamping each layer 25 times with a

standard rod.

(iii) Weight the test sample (say ) and place it in the test cylinder and tamp each layer 25

times with standard rod.

(iv) Place the plunger on the top of the test specimen and put the whole apparatus in the

compression testing machine.

(v) Load the specimen with a total load of 40 tonnes @ 4 ton / minute.

(vi) Remove the test cylinder from the compression machine and sieve the aggregate through

2.36 mm sieve. Weight the material passing through (say ).

For surface course, crushing value 30 %

For base course, crushing value ≤ 45 %

2. Abrasion test

Abrasion tests are carried out to test the hardness property of stones and to decide

whether they are suitable for the different road construction works.

The abrasion test on aggregate may be carried out by;

Los Angeles Abrasion Test

Principle

The principle of Los Angeles Abrasion Test is to find the percentage wear and tear due to

relative rubbing action between the aggregates and steel balls used as abrasive charge.

Equipment

(a) Hollow cylindrical machine with 70 cm internal diameter and 50 cm long mounted on

supports.

(b) Steel spherical balls 4.8 cm dia. and weighing 390 – 445 grams.

Procedure

(i) Weight the aggregate sample (5 kg or 10 kg) depending on the grading ( ) and place in

machine.

(ii) Rotate the machine with a speed of 30 – 33 rpm for the specified number of revolution

(500 – 1000).

(iii) Take out the sample from the testing machine and sieve through 1.7 mm sieve. Weight the

aggregate passing through (say ).

For cement concrete, abrasion value 16 %

Bituminous mix surface course, abrasion value ≤ 30 %

Bituminous with base course, abrasion value ≤ 50 %



3. Impact test

A test designed to evaluate the toughness of stone or the resistance of the aggregates to

fracture under repeated impacts is called impact test.

- The aggregate impact value indicates a relative measure of resistance of aggregate to

impact, which has a different effect than the resistance to gradually increase compressive

stress.

Equipment

(a) A steel cylindrical cup of internal dia. 10.2 cm and 5 cm depth in which the aggregate

sample is placed.

(b) A metal hammer having a weight of 13.5 to 14 kg and having a free fall of 38 cm.

(c) Tamping rod 60 cm long and 1.6 cm diameter.

Procedure

(i) Fill the dry aggregate specimen in cylindrical cup of an impact test machine passing 12.5

mm sieve and retained on 10 mm sieve in 3 equal layers and tamp each layer by 25 blows

with tamping rod and weigh it (say ).

(ii) Raise the hammer to a height of 38 cm above the surface of the aggregate in the cup and

is allowed to fall freely on the specimen. 15 blows are given to the aggregate specimen.

(iii) Sieve the aggregate sample through 2.36 mm sieve and weight (say ).

Impact value, 10 – 30 % satisfactory strong

Impact value, 30 % surface or wearing course

Impact value, < 45 base course

4. Soundness test

Soundness test is intended to study the resistance of aggregates to weathering action,

by conducting accelerated weathering test cycle.

Procedure

(i) Weight and count the dry and clean aggregates of specified size.

(ii) Immense the piece in the saturated solution of sodium sulphate or magnesium sulphate for

16 – 18 hrs.

(iii) Oven dry the specimen at 105o – 110o C.

(iv) Immersion and drying is the one cycle.

(v) After completing the final cycle, dry the sample and examine the piece of aggregate visually

to seed excessive splitting, crumbing or disintegration of grains.

(vi) Sieve analysis to note the variation of gradation from the original.

(vii) The average loss in weight after 10 such cycles should not exceed 12 % (for test with sodium

sulphate) or 18 % (for test with magnesium sulphate) for aggregates to be of

recommendable quality.



Gradation Analysis of Aggregate Gradation analysis usually involves the gradation test. From the gradation test,

determine the weight retained, cumulative weight retained on each sieve and total weight

passing on each sieve.

- Compare the gradation curve obtained with the gradation curve in the specification.

- The blending of aggregates to desired gradation is a complicated problem, particularly when

the two aggregates are to be combined and these gradation overlap.

- This can be done by two methods:

1. Mathematical method 2. Graphical method

1. Mathematical method

An equation of the general form is:

Where,

a, b & c = proportion of the mix to be taken from aggregate A, B & C respectively

A, B & C = % particles either retained or passing on each sieve

T = specified mix value

Example:

B.S. sieve (mm)

% passing given sieve size

F.A. (A) M.A. (B) C.A. (C) specifications

Limit mid value

25.4 100 100 100 100 100

12.7 100 100 94 90 - 100 95

4.76 100 100 54 60 - 75 67.5

1.18 100 66.4 31.3 40 - 55 47.5

0.3 100 26 22.8 22 - 35 27.5

0.15 73.6 17.4 9 12 - 22 17

0.075 40.1 5 3 5 - 10 7.5

(a) For % passing through 4.76 mm sieve, 100a + 100b + 54c = 67.5

For % retained through same sieve, 0a + 0b + 46c = 32.5 ---------- (i)

c = 0.71

(b) For % passing through 1.18 mm and 0.3 mm sieve

100a + 66.4b + 31.3c = 47.5 --------- (ii)

And 100a + 26b + 22.8c = 27.5 --------- (iii)

Subtracting (iii) from (ii) we get

40.4b + 8.5c = 20 -------- (iv)

Putting the value of c from (i) in (iv), we get

b = 0.35

Also, a + b + c = 1 a = - 0.06

Negative value indicates mid-point specification is do no match, so repeat using the

specification of 70 % passing from 4.75 mm & 45 % passing for 1.18 mm sieve.

i.e. 0a + 0b + 46c = 30 ---------- (v)

c = 0.65



Now for 1.18 mm and 0.3 mm sieve (% passing)

100a + 66.4b + 31.3c = 45 --------- (vi)

And 100a + 26b + 22.8c = 27.5 --------- (vii)

Form (vi) and (vii)

40.4b + 8.5c = 17.5 ---------- (viii)

b = 0.3

Also, a + b + c = 1 or, a + 0.3 + 0.65 = 1 a = 0.05

I.e. a = 5 %, b = 30 %, c = 65 %

Desired gradation is tabulated as:

B.S. sieve (cm)

Aggregate

A5% (i)

Aggregate

B30% (ii)

Aggregate

C65% (iii) Combining (i)+(ii)+(iii)

25.4 1000.05=5 1000.3=30 1000.65=65 100

12.7 5 30 61 96

4.76 5 30 35.1 70.1

1.18 5 19.9 20.3 45.27

0.3 5 7.8 14.8 27.62

0.15 3.7 5.3 5.9 14.9

0.075 2 1.5 2 5.5

BITUMINOUS MATERIALS Bituminous binders used in pavement construction works include both bitumen and tar.

- Bitumen is a petroleum product obtained by the distillation of petroleum crude whereas

road tar is obtained by the destructive distillation of coal or wood.

Types of Bituminous materials

Bituminous materials used in highway construction may be classified as:

1. Bitumen (i) Native bitumen or asphalt

(ii) Petroleum bitumen or asphalt

2. Tar

- 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 asphalt.

- The viscosity of bitumen is reduced sometimes by a volatile diluent; this material is called

cutback.

- When bitumen is suspended in a finely divided condition in an aqueous medium and

stabilised with an emulsifier, the material is known as emulsion.

Bitumen Bitumen is a petroleum product obtained by the distillation of petroleum crude. It is the

product of fractional distillation of crude oil.



Requirements of Bitumen

(i) Mixing

(ii) Attainment of desired stability of the mix

(iii) To maintain the stability under adverse weather condition

(iv) To maintain sufficient flexibility and thus avoid cracking of bituminous surface

(v) To have sufficient adhesion with the aggregates in the mix in presence of water

Desirable properties of Bitumen

The bitumen should possess the following desirable properties:

(i) The viscosity of the bitumen at the time of mixing and compaction should be adequate.

(ii) The bituminous material should not be highly temperature susceptible. I.e. during the

hottest weather the bituminous mix should not become too soft or unstable and during cold

weather the mix should not become too hard and brittle causing cracking of surface.

(iii) In presence of water the bitumen should not strip off from the aggregates. There has to be

adequate affinity and adhesion between the bitumen and aggregates used.

Comparison between Bitumen and Tar

Bitumen Tar

1. It is the product of fractional distillation of crude oil (i.e. petroleum crude).

2. It has black to dark brown colour. 3. It is soluble in and 4. It has better weather resisting property. 5. It is less temperature susceptible. 6. It contains less free carbon.

1. It is the product of destructive distillation of coal or wood.

2. It has black to dark brown colour. 3. It is soluble in toulene. 4. It has poor weather resisting property. 5. It is more temperature susceptible. 6. It contains more free carbon.

Tests on Bitumen

1. Penetration test 2. Ductility test 3. Viscosity test

4. Softening point test 5. Sp. Gravity test 6. Float test

7. Solubility test 8. Flash and fire point test 9. Spot test

1. Penetration Test

This test determines the hardness or softness of bitumen by measuring the depth in mm

to which a standard loaded needle will penetrate vertically in five seconds while the

temperature of the bitumen sample is maintained as 25oC.

Equipment

- A penetration consisting of a needle assembly with a total weight of 100 mg and device for

releasing and locking needle in any position.

- A graduated dial gauge to read the penetration value up to 0.1 mm.

Procedure

(i) The bitumen is softened to a pouring consistency, stirred thoroughly and poured into

containers to a depth at least 15 mm in excess of the expected penetration.

(ii) The sample containers are then placed in a temperature controlled water bath at a

temperature of 25oC for 1 hour.

(iii) The sample with container is taken out and the needle is arranged to make contact with the

surface of the sample.



(iv) The dial is set to zero or the initial reading is taken and the needle is released for 5 sec.

(v) The final reading is taken on dial gauge.

(vi) At least 3 penetration tests are made on this sample by testing at distances of at least 10

mm apart.

(vii) The depth of penetration is reported in one-tenth millimetre units and the mean value of 3

measurements give a penetration value.

(viii) The bitumen grade is specified in terms of penetration value. 80 – 100 or 80/100 grade

bitumen means that the penetration value of the bitumen is in the range 80 to 100 at

standard test conditions.

2. Ductility test

Ductility is a means of elasticity or adhesiveness of bitumen. It is expressed as the

distance in to which a standard briquette can be stretched before the thread breaks.

- The test should be conducted at 27oC and the pull should be applied @ of 50 mm/min.

- The minimum width of x-section should be 10 10 mm.

Equipment

» Briquette of standard dimension

» Pulling device with distance measuring dial

Procedure

(i) Heat the bitumen sample to bring it in fluid state and pour the briquette assembly and place

on a brass plate.

(ii) The samples along with the moulds are cooled in air and then in water bath maintained at

27oC.

(iii) The excess bitumen material is cut and the surface is levelled using a hot knife.

(iv) The mould assembly containing sample is replaced in water bath of the ductility testing

machine for 85 – 95 minute.

(v) The sides of the mould are removed, the clips hooked on the machine and the pointer is

adjusted to zero.

(vi) The distance up to the point of breaking of thread is reported in as ductility value.

(vii) The ductility values of bitumen vary from 5 to 100 cm for different bitumen grades.

3. Viscosity test

Viscosity is defined as inverse of fluidity. Viscosity thus defines the fluid property of

bituminous material.

- The degree of fluidity of the binder at the application temperature greatly influences the

strength characteristics of the resulting paving mixes.



- It is applicable for both cut back and tars.

- It is the measurement of resistance to flow.

- Viscosity is measured by recording the time in seconds taken by 50 cc of material to flow

through specified orifice of standard dimension at standard temperature.

Tar: (Equipment)

» An orifice of 10 mm size (orifice viscometer)

» Sample collected

» Thermometer

Procedure

Note the time in seconds for 50 cc of sample to flow through the orifice of 10 mm at the

specified temperature of 35, 40, 45 or 55oC.

Cutback: (Equipment)

An orifice of 4 mm at 25oC or 10 mm at 25 – 40oC

Sample collected

Thermometer

Procedure

Note the time in seconds for 50 cc of sample to flow through 4 mm orifice at 25oC or 10

mm orifice at 25 – 40oC.

4. Softening point test

Softening point is defined as the temperature at which a substance attains a particular

degree of softening under specified conditions.

- Softening point is determined by ring and ball test.

- Generally higher softening point indicates lower temperature susceptibility and is preferred

in warm climates.

Equipment

A brass ring and steel ball

Water bath and thermometer

Procedure

(i) A brass ring containing test sample of bitumen is suspended in liquid like water or glycerine

at a given temperature.

(ii) A steel ball is placed upon the bitumen and the liquid medium is then heated at a rate of 5oC

per minute.

(iii) The temperature at which the softened bitumen touches the metal placed at a specified

distance below the ring is recorded as the softening point of bitumen.

Hard grade bitumen possesses higher softening point than soft grade bitumen. The

softening point of various bitumen grades used in paving jobs vary between 35 – 70oC.



Cutback bitumen Cutback bitumen is defined as the bitumen, the viscosity of which has been reduced by a

volatile solvent. Kerosene oil or diesel is used as the volatile solvent.

Purposes

To increase fluidity for good mixing and such mix can be transported for long haul

without setting.

Types

(i) Slow curing (SC)

It is 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.

- It is used in fine cold asphalt and as dust palliative materials.

(ii) Medium curing (MC)

These are bitumen fluxed to greater fluidity by blending with an intermediate-boiling-

point solvent like kerosene or light diesel oil.

- It is used in dense graded road surfacing / in bituminous soil stabilisation.

(iii) Rapid curing (RC)

These are bitumen, fluxed or cutback with a petroleum distillate such as neptha or

gasoline which will rapidly evaporate after using in construction, leaving the bitumen

binder.

Bitumen 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 stabilised by means of

one or more suitable materials.

- Emulsions are used in bituminous road construction, especially in maintenance and patch

repairing works.

- The main advantage of emulsion is that it can be used in wet whether even when it is

raining.

- Also, emulsion has been used in soil stabilisation, particularly for the stabilisation of sands in

desert areas.

Types

i) Rapid setting (RS)

Suitable for surface dressing and penetration macadam type of construction.

ii) Medium setting (MS)

Used for premixing with coarse aggregates.

iii) Slow setting (SS)

Suitable for fine aggregate mixes.



Tar Tar is the viscous liquid obtained when natural organic materials such as wood and coal

carbonised or destructively distilled in the absence of air.

Three stages for the production of road tar are:

(i) Carbonisation of coal to produce crude tar

(ii) Refining or distillation of crude tar

(iii) Blending of distillation residue with distillate oil function to give the desired road tar.

Following are the grade of road tars.

i) RT – 1 : it has lowest viscosity and used for surface painting

ii) RT – 2 : used for standard surface painting

iii) RT – 3 : used for surface painting, renewal coats and premixing chips

iv) RT – 4 : used for premixing the macadam in base course

v) RT – 5 : used for grouting purpose and has highest viscosity among the road tars

BITUMINOUS MIXES Bituminous mixes are composed of a mixture of aggregate (coarse aggregate and fine

aggregate) with bitumen or without filler.

Coarse aggregates

- Material retained on 2.36 mm sieve

- Imparts stability to the mix by mechanical interlock between the particles.

- Resists the abrasive action of traffic

Fine aggregates

- Materials passing through 2.36 mm sieve and retained on 75µ sieve.

- Fill the voids of the coarse aggregates and help to secure dense gradation.

Filler

- Materials passing through 600 micro sieve.

- Acts as a final void filling medium and complete the process of making the mixture as

dense as possible.

Desirable Properties of Bituminous Mixes

i) Sufficient stability to satisfy the service requirements of the pavement and the traffic

conditions, without undue displacements.

ii) Sufficient bitumen to ensure a durable pavement by coating the aggregate and bonding

them together and also by water-proofing the mix.

iii) Sufficient voids in the compacted mix as to provide a reservoir space for a slight amount of

additional compaction due to traffic and to avoid flushing, bleeding and loss of stability.

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.



Design Steps of Bituminous Mixes

The following steps may be followed for a rational design of a bituminous mix:

1) Selection of Aggregate

Aggregates which possess sufficient strength, hardness, toughness and soundness are

chosen keeping in view the availability and economic consideration.

- Crushed aggregates and sharp sands produce higher stability of the mix when compared

with gravel and round sands.

2) Selection of Aggregate Grading

As higher maximum size of aggregate gives higher stability.

- In base course maximum aggregate size of 2.5 to 5 cm are used whereas for surface course

1.25 to 1.87 cm size are used in the mixes.

3) Determination of Specific gravity

The sp. gravity of the total or combined aggregate is determined and the average

specific gravity ( ) of blended aggregate mix is given by;

⁄ ⁄ ⁄ ⁄

Where, are percent by weight of aggregates 1, 2, 3 & 4.

are the specific gravities of the respective aggregates.

4) Selection of Binders

It depends upon the nature of traffic and climatic condition. Penetration grade bitumen

are considered suitable.

5) Determination of Optimum bitumen content

- To ensure maximum stability.

- Resistance of the paving mix to deformation under load.

Marshall Stability Test for Bituminous Mix Design Marshall Stability method is a type of unconfined compressive strength test in which a

cylindrical specimen of specified diameter and height is compressed radially at a constant

rate strain.

- The maximum load in sustained by the specimen at failure is called Marshall

Stability Value.

- The deformation in at failure is called Marshall Flow Value.

Equipment

(i) A cylindrical mould of 101.6 dia. and 63.5 mm height with a base plate and collar.

(ii) A hammer of 4.54 kg weight.

(iii) A sample extractor to extrude the compacted specimen from the mould.

(iv) Dial gauge to measure the deformation of the specimen and providing ring to measure the

load.



Procedure

i) Take 1200 mg of aggregates and heat up to 154oC to 160oC.

ii) Assume the bitumen content and heat separately up to 175 – 190oC.

iii) Mix thoroughly aggregate and bitumen such that the upper surfaces of the aggregate

appear to be uniformly coloured with bitumen fill.

iv) Pour the mix into the Marshall mould.

v) Compact mix with hammer weight 4.54 kg & free fall 457 mm with 50 blows on either side.

vi) Taken out the mould and kept under laboratory temp. for 12 hrs.

vii) Immerse the specimen at water bath with constant temperature 60oC for 30 minutes.

viii) Now put the sample for testing in Marshall Testing Machine and apply load vertically @ 50

mm/min. on the sample at 60oC.

ix) Max load at which sample fails gives the Marshal Stability value.

x) Measure the flow value from the dial gauge reading.

2009 fall 6.(b)

Solution:

Here, wt. of mix in air ( ) = 1180.5 gm

wt. of mix in water ( ) = 678.6 gm

(i) Bulk density of specimen form dimension and immersion test:

Bulk density

⁄

⁄ = 2.275 gm/cm

3

(ii) Air void % in compacted mix:

(iii) VMA (Voids in Mineral Aggregate):

Here,

VMA = 2.76 + 13.84 = 16.6 %

(iv) VFB (% voids filled with bitumen):

Where,

= % by wt. of bitumen, coarse agg, fine agg and mineral filler resp.

= respective apparent sp. gravity.



[8] GREEN ROADS

Intro

Green roads are low cost, low volume, fair weather earthen road. They are usually

village roads or district roads under rural road network.

- The green road concept is an approach; it refers to and environmentally sound, affordable

(low cost), participatory, technically appropriate, labour based rural road.

- The green road concept focussing on the protection of vegetation cover as means of soil

conservation without using heavy equipment and rock blasting.

Design consideration

Maximum gradient 12 %

Minimum radius of horizontal curve = 12.5 m

Pavement surface is earthen with spot graveling at places wherever required.

Other geometric design standards are similar to that of standard road practice.

Objectives

i) Since it is labour based construction, so labour cost is about 65 % of total construction cost.

ii) The participation of politicians, users committee and technician is essential.

iii) Heavy equipment is not used and rock blasting is not permitted.

iv) In the beginning, track of 1 – 1.5 m is opened and it is then gradually expanded to required

width.

v) Constructing rural roads following the green road approach offers several benefits over

tradition roads construction.

- It is affordable as the construction technique uses local material and people to construct

road.

- It is participatory, since different stack holders are actively engaged from planning to

operation and maintenance of the road.

- Since it uses local labour and materials, it has an immense potential for poverty

alleviation.

- Environmental protection is a key aspect of green roads.

The End

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