The order of the components of a typical flexible pavement from bottom to top is:
Flexible pavements are so named because the total pavement structure deflects or flexes under loading. A flexible pavement structure is composed of several layers of materials. Each layer receives load from the above layer, spread them out and passes on these loads to the next layer below. Thus the stress will be reduced which is maximum at the top layer and minimum on the top of the subgrade.
The typical flexible pavement has the following components, and which are shown in Figure
(a) Soil sub-grade
(b) Sub-base course
(c) Base course
(d) Surface course
In order to take maximum advantage of this property of load transfer, layers are usually arranged in descending load-bearing capacity. Most expensive at the top and least expensive at the bottom.