Pavement thickness design - flexible pavements

Pavement thickness design is dependent on a number of factors such as the traffic volume and composition, the reaction of the subgrade to changes in moisture content and the riding quality. The greatest impact on thickness design results from variation in the values adopted for subgrade strength which leads to the need for accurate assessment of the subgrade CBR. The designer should be fully aware of the many factors that affect pavement design and that complete reliance on design procedure can be misleading unless a full evaluation of all the factors affecting the design is made. This paper describes methods of flexible pavement design used by the Main Roads Department, Western Australia for designing flexible pavements with unbound layers which are to receive both thin and thick layers of asphalt, bound layers or asphalt layers in excess of 100 mm. The thickness design of an overlay required to rehabilitate a pavement where the deficiency has resulted from inadequate base course thickness is discussed in detail (a).