Failure analysis of a semi structural pavement using a mechanistic tool – case study for a provincial road

Pavement design is a vital part in new road construction and in rehabilitation projects. Conventional flexible pavements are layered systems with high stress intensity on top and low intensity at the bottom. AASHTO method is widely used by most of the road agencies to design pavements while the Transport Research Laboratory (U.K) Road Note 31 (TRL RN-31) specifies for the tropical countries. Both these design guidelines are based on empirical formula or experimental studies conducted in extreme weather condition. Road Note 31 specifies the layer thicknesses of specific materials. It does not specify a method to adopt the materials that does not fit the specifications, which is the commonly encountered problem due to the varying site condition and availability of materials. Empirical design methods do not have any provision for analysing road failures and propose most suitable rehabilitation method. Therefore this research focused on evaluating the suitability of a mechanistic empirical pavement design tool to investigate a pavement failure. In this study, failure of a Sri Lankan rural road which is failed immediately after completing the construction was selected for the analysis. This road was designed according to the Overseas Road Note 31(ORN 31) as a Double Bitumen Surface Treatment (DBST) road and it has shown longitudinal cracking on the surface followed by the depression and the settlement, approximately after six months from the completion. Heavy axle load applied on the pavement due to transporting of construction materials to a new project has increased the propagation of cracks and potholes. Soil samples collected from the critically damaged locations were tested and the results showed that the inadequate strength of the pavement structure as the cause to the failure. Failure investigations were done using a mechanistic tool called CIRCLY and reliable reclamation method was proposed