.Conventional road structures
The earliest form of road consisted of an earth track which had been cleared of vegetation and compacted by human and animal traffics . Recently , the need for cheap and efficient roads has resulted in the technical developments of earth road construction in which use has been made of soil and low grade aggregate .
The road is usually built up in several layers , each having some special functions. As with modern forms of a road , the construction comprises of a subgrade layer followed by the construction of a base material layer and laying of surfacing , as shown in figure (I.7)
The chief function of surfacing is to provide a wear surface.However the surfacing is sometimes omitted for cheapness. Very often, on poor subgrade, a sub-base layer of compacted gravel or stabilized soil is given to distribute the load properly and prevent the clay working up into the base (22)