A combined method to predict the long-term settlements of roads on soft soil under cyclic traffic loadings

In order to investigate the mechanism of the long-term settlement of road on the soft soil, an in situ measurement of a highway in southeast China was conducted during both the construction and post-construction stage. In the theoretical analysis, the long-term settlement of the pavement on thick soft soils was divided into three main components: the consolidation settlement, the creep deformation and the traffic load-induced deformation. The equivalent time line model based on the viscous-elastic-plastic theory was adopted to simulate the road settlement caused by the consolidation and creep of the subsoil. A cyclic strain accumulation model, which was obtained from laboratory tests of soil elements, was adopted to consider the road settlement induced by cyclic traffic loadings. A pavement dynamic response model was used to calculate the dynamic stresses in the subsoil generated by moving traffic loads when the road was open to service. It was found that the equivalent time line model combined with the cyclic strain accumulation model could predict the road settlement accurately at both the construction and post-construction stage. Numerical results showed that the traffic speed had limited effect on the post-construction road settlements for the speed range considered. The post-construction settlement of the road, mainly composed of the traffic-induced settlement and soil creep deformation, could be reduced significantly by increasing the embankment surcharge during the construction stage. The creep component accounted for over 10% of the total post-construction settlement, while the percentage of the creep deformation in total post-construction settlement decreased rapidly as the embankment surcharge increased.