建立准确合理的接触面本构模型是研究桩基承载力、沉降及变形等问题的前提。考虑桩-土界面初始剪切刚度的深度效应，提出基于统计损伤本构模型的无厚度接触面本构模型，根据剪切试验的数据对改进的接触面本构模型参数进行拟合，得到了不同法向应力下的模拟曲线。利用FLAC3D软件内嵌的FISH语言，对桩-土界面进行改进本构模型的二次开发，提出的无厚度接触面模型合理地模拟出桩-土界面刚度的非线性，成功实现了桩-土剪切试验过程的数值模拟。计算结果表明：提出的无厚度接触面本构模型能够合理地模拟桩-土界面的力学行为，可以描述接触面刚度的非线性变化，也适于程序化计算，拓展了接触面统计损伤本构模型的应用领域，为深入探讨桩基承载变形性状奠定了基础。

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.