Lower shakedown limits of layered road structures under moving harmonic loads

The shakedown limits of layered road structures subjected to a moving harmonic load are studied. The inverse Fourier transform and the numerical integration are used to obtain the dynamic responses of a three-dimensional layered road structure in the time and space domain. Considering the effective stress field of saturated subsoil instead of the total stress field, the existing static shakedown theorem and the solving method for the shakedown limits are improved, and the concept of the effective shakedown limit is proposed and compared with the solving method for the shakedown limits considering the total stress. In addition, different effective internal friction angles are selected for the saturated soil layer, and the influences of load-moving speed, load frequency and pavement stiffness on the effective shakedown limit and effective critical depth of the layered road structure are studied respectively. The results show that there is a significant difference between the effective shakedown limits and the shakedown limits obtained by the solving method for the shakedown limits considering the total stress. Moreover, the effective critical depth is deeper than that obtained by the solving method for the shakedown limits considering the total stress when the load-moving speed is relatively high. The proposed method for solving the effective shakedown limits is more suitable for the design and safety assessment of layered road structures containing saturated soil layers.