What is Method of Construction of Gravel Roads?

Construction of Gravel Roads

Gravel roads are considered superior to Earthen Roads as they can carry heavier traffic.

this type of road can take about 100 tonnes of Pneumatic tyred vehicle or 60 tonnes of iron tyred vehicles per day per lane. 

the camber provided on this type of road is between 1 in 25 and 1 in 30.

Two types of Construction methods are given below.

(I) Feather Edge Type

it is Constructed over the Subgrade with varying thickness, so as to obtain the desired cross slope for the pavement surface.

(II) Trench Type

in the trench type, the Subgrade is prepared by excavating a shallow trench. 

Figure:-(1) Types of gravel road sections

The Construction of Gravel Roads may be divided into following steps.

(I) Construction Material

Hard variety of crushed stone or gravel of specified gradation is used. 

Rounded stones and river gravel are not preferable as there is poor interlocking. 

Gravel to be used for the construction is stacked along the sides of proposed road.

(II) Alignment Location

the central line and Road ages are marked on the ground along the alignment with the help of reference pegs.

(III) Pavement Structure

the layer is rolled using smooth wheel rollers starting from the edges and proceeding towards the centre with an overlap of atleast half the width of roller in the longitudinal direction.

 (IV) Opening to Road Traffic 

A few days after the final rolling and drying out, the road is opened  to the traffic. 

What is Construction of Earthen Roads,Types of Highway Construction

Types of Highway Construction

the highway construction types are various given below.

(1) Earth roads.    (2) Gravel road

(3) Soil Stabilized Roads 

(4) Water Bound Macadam (WBM) Roads

(5) Bituminous Roads

(6) Cement Concrete Roads

Construction of Earthen Roads 

an earthen road is the cheapest type of road prepared from natural soil. 

the pavement Section is totally made up of the soil available at site.

the maximum cross slope 1 in 2 is recommended to avoid erosion due to rain water and formation of cross ruts. the steep cross slope helps to keep the pavement surface free of standing water, otherwise the soil being previous the water would damage the pavement Section by softening.

the Construction of Earthen Roads  may be divided into following steps.

(a)  Construction Material

the pavement Section is totally made up of the soil available at site or nearby which is free from organic substances.

(b) Alignment Location

the centre line and road edges are marked on the ground along the road alignment by dividing wooden pegs .

the spacing of reference pegs depends on the estimated length of road Construction in a day.

(c) Preparation of Sub- Grade

the various operations involved in the Construction of sub Grade are clearing site, Excavation and Construction of soil fills to bring the road to a desired grade and shaping of sub grade.

(d) Construction of Pavement Structure

the soil is mixed, spread and rolled in Layers such that the Compacted thickness of each layer does not exceed 10 Centrimeter.

At least 95% of maximum dry density (MDD) is considered desirable

(e) Opening to traffic

The Compacted earth road is allowed to dry out for a few days before opening to traffic.

Design Elements in Highway Embankments

The Design Elements of highway embankment are following points.

(1) Height:- the height of embankment depends on the desired grade line of the highways, topography, stability of foundation and the soil Profile.

(2) Embankment Material:- Granular Soil is generally preferred as Highway Embankment Material.

The best of the soils existing locally is often selected with a view to keep the lead and lift as low as possible.

(3) Settlement of Filling Material:-

If the embankment foundation consists of compressible soil with high moisture content, the consolidation can occur due to increase in the load. 

To accelerate the rate of consolidation of saturated foundation clay, vertical drains are Constructed.

(4) Stability of Foundation:-

Stability of Foundation is required in case of weak soil just beneath or at a certain depth below of embankment foundation and in case of high Embankments.

(5) Stability of Slope:- 

The Embankment slopes should be stable enough to eliminate the possibility of a failure under adverse moisture and other conditions.

Often much flatter slopes are preferred in Highway Embankment due to aesthetic and other reason.