Permanent settlement of subgrade of saturated soft soils

Under vehicle loads, the permanent settlement of highway pavement is induced, especially in the Yangtze River Delta area, the traffic loading induces the degradation of the strength and stiffness and the accumulation of the excess pore pressure. Based on the former cyclic triaxial test results, a new degradation of stiffness model is proposed, which is expressed by the effective stress increment compared with the initial condition divided by the corresponding deformation, and a formula for the effective stress is established. Moreover, by combining with the layer-wise summation method, a method is suggested to estimate the long-term settlement of soft ground caused by traffic loads. The calculated results show that the settlement increases rapidly in the early phase, then tends to stable. Because the stiffness of the pavement layer is very large, the compression deformation is very small, and the settlement of road surface is mainly composed of the deformation of the 4th layer of silt clay. Due to the stress dispersion, the vertical dynamic deviator stress of the 5th layer of silt is small, so its settlement is very small.