GRAVEL ROADS
The roads which consist of one or two layers of compacted gravel mixed with sand and clay are called gravel roads. These roads are considered as low-cost roads and provide better traffic capacity then earth roads. A chamber of 1 in 30 is required for these roads. These roads are constructed as a village or other district roads.
METHOD OF CONSTRUCTION
THESE ROADS ARE CONSTRUCTED BY THE FOLLOWING TWO METHODS:
Feather Edge Method
Trench Method.
Feather Edge Method
In this method, the gravel mix is directly laid on the prepared horizontal sub-grade. This method does not provide any lateral stability to the road metal. The gravel road constructed by this method is called Feather Edge type gravel road. This method is rarely used in India country.
Trench Method
This the method is superior to the Feather Edge method and is most commonly used country. In this method, the sub-grade is prepared by excavating a shallow trench. This method provides good lateral stability to the gravel.
Following steps are followed in the construction of gravel roads:
1) First of all the sub-grade is prepared and the road surface is brought to the required camber and gradient. This prepared surface is then properly compacted.
2) After compaction of sub-grade, the mixture of gravel and clay is spread with more thickness at the center and loss thickness towards the edges so that a required camber is provided. Clay in the mix acts as a binder for gravel and sand.
3) The gravel mix so spread is then compacted to the required camber. The size of gravel ranges between 6 mm to 35 mm. This surface is rolled with a light roller until the required compaction is achieved.
4)This compacted surface is then watered for 4 to 5 days for curing. During this period of curing traffic is not allowed to pass through the surface.
5) After curing the road is opened to traffic but the water is sprinkled on the surface for further ten to fifteen days.
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