Transportation Engineering
Civil Engineering

Extra Points

Camber

Camber is the slope provided in the transverse direction of the road to drain off the rain water from the road surface. Usually camber is provided in the straight roads by raising the centre of the carriage way with respect to the edges forming highest point at the centre.

Straight slope of camber is easier to be cast and maintained in case of concrete pavement. Parabolic shaped camber is difficult to construct and maintain. It has more steeper edges which are inconvenient to use. However, it is kept in bituminous pavements for better drainage of water.

Pavement and its Shape of camber

Cement concrete = pavementStraight
Bitumen pavement =Parabolic

Type of Explosive	Suitability
Blasting Powder	In large quarrying blocks
Dynamite	Small boreholes and quarries
Cordite and Gelignite	Under water
Lithofracteor	Tunnels

Kerbs

Kerb and its Height abovethe pavement
1.Mountain kerb = 10 cm
2.Semi-barrier type kerb = 15 cm
3.Barrier type kerb = 20 cm

Off Tracking Formula

The off-tracking on the road is given by:

Eoff = nLsquare/2R

where

n = number of lanes

L = wheel base

R = Radius of the curve

Eoff = Off-tracking

Temperature stresses and Variations

Temperature stresses are developed in rigid pavements due to variations in temperature. This is caused by the following two factors:

1. Seasonal variation in temperature and

2. Daily Variation in temperature

Statement I – False

Daily variation in temperature:

It causes warping stress due to the temperature gradient across the slab thickness.

During the day, the top surface will try to expand but the weight of the slab will resist and hence, compression will be developed on the top surface and tension will develop at the bottom surface.

During the night, the bottom surface will be at a higher temperature and hence, has a tendency to expand, but the weight of the slab will resist it, generating compression at the bottom surface and tension at the top surface.

During Day Time:

During Night Time:

During the day the top of the pavement slab gets heated under the sunlight when the bottom of slab still remains relatively colder.

Seasonal Variation in temperature

It causes frictional stresses due to the overall change in the temperature of the slab. During summer season as the mean temperature of the slab increases, the concrete pavement expands towards the expansion joints and in winter season opposite phenomena occurred as shown in the figure:

Frictional Stresses:

Durring summer

Durring winter

Floating gradient:- The gradient on which a motor vehicle moving with a constant speed continues to descend with the same speed without any application of power brakes is called floating gradient i.e the vehicle does not require any tractive effort to maintain the specific speed.

Minimum gradient:- The minimum desirable slope essential for effective drainage of rainwater from the road surface is called minimum gradient

Exceptional gradient:- The gradient steeper than the limiting gradient which may be used in short length of road, only in an extraordinary situation is called exceptional gradient.

Ruling gradient:- The gradient usually adopted while making the road alignment is called the ruling gradient. It is the maximum gradient within which the designer attempts to design the vertical profile of a road. It is also known as design gradient.

Nagpur road plan or First 20 year road plan (1943 - 63):

In this plan road network in the country was classified in to:
i) National Highways
ii) State highways
iii) Major District roads
iv) Other District roads
v) Village roads

In the Nagpur conference, recommendations were made for the geometric standards of roads, bridge specifications and highway organisations and two plan formulae were finalised. This two plan formulae assumed star and Grid pattern of road network.

Note:

1. The rectangular or the block pattern has been adopted in the city roads of chandigarh.
2. Radial and circular pattern of road network is adopted in Connaught place (New Delhi).

Flexible Pavement

A pavement which consist of a mixture of asphaltic or bituminous material and aggregate placed on a good quality and compacted granular material is termed as flexible pavement. The flexible pavement has low or negligible flexural strength. Example-Water bound macadam roads.

Water bound macadam roads:

The roads whose wearing course consist of clean crushed aggregates, mechanically interlocked by rolling and bound together with filler material and water and laid on a well compacted base course, is called water bound macadam road.

California Bearing Ratio (CBR) test:

California Bearing Ratio (CBR) test is a method of classifying and evaluating soil-subgrade and base course materials for flexible pavements.

CBR test, an empirical test, has been used to determine the material properties for pavement design.

This test measures the strength of the material and is not a true representation of the resilient modulus.

It is a penetration test wherein a standard piston, having an area of 3 in 2 (or 50 mm diameter), is used to penetrate the soil at a standard rate of 1.25 mm/minute.