Abstract: Establishing an accurate and reasonable contact surface constitutive model is the premise to investigate the bearing capacity, settlement and deformation of a pile foundation. By considering the depth effect of initial shear stiffness of the pile-soil interface, a zero-thickness contact surface constitutive model is developed based on the contact surface statistical damage constitutive model. Parameters of this model are fitted by shear experimental data. Simulation curves under different normal stresses are obtained and compared with experimental results. A corresponding calculating program is developed by implementing the FISH language into FLAC3D software to realize a secondary development of the pile-soil improved contact surface constitutive model. The developed model demonstrates that it is reasonable for calculating the nonlinear behaviour of the pile-soil interface stiffness, which is further used to realize numerical simulation of the pile-soil shear test. Numerical results indicate that the developed model can be successfully applied to simulate mechanical behavior of the pile-soil interface, and to describe the nonlinearity of the pile-soil contact surface stiffness well. Furthermore, it is suitable for programming calculation, and it broadens the application of the statistical damage constitutive model and establishes a foundation for the further study on characteristics of pile foundation bearing and deformation.

Key words: pile-soil interface, zero-thickness contact surface, statistical damage constitutive model, numerical simulation