为了全面地了解降雨入渗引起的边坡失稳破坏机制，基于有限元-有限差分理论（FE-FD scheme）的水-土-气三相渗流-变形耦合有限元数值分析方法被提出。程序中采用了Zhang等[1]提出的以Bishop有效应力和饱和度作为状态变量的非饱和土弹塑性本构模型，从而可以连续地描述在降雨入渗时土体由非饱和状态转化为饱和状态过程中力学特性的变化。同时用Green-Naghdi客观应力速率张量来考虑边坡失稳过程中的大变形问题。程序不仅可以模拟由于降雨入渗引起的水分迁移、孔隙水/气压力变化的过程，而且可以很好地反映出由于降雨入渗所引起的边坡变形、塑性剪切带形成等力学行为。选取室内边坡模型试验为研究对象，用所提出的水-土-气三相渗流-变形耦合有限元程序来进行数值模拟，并与试验结果对比，验证了所提出的有限元数值方法的有用性。

In order to understand the failure mechanism of slope due to rainfall infiltration, a soil-water-air seepage-deformation coupling finite element program is developed based on finite element-finite difference scheme. In the program, the unsaturated elastoplastic constitutive model using Bishop effective stress and degree of saturation as state variables, proposed by Zhang et al[1], is used to describe the mechanical behaviors of soil from unsaturated state to saturated state due to rainfall infiltration. Meanwhile, Green-Naghdi stress rate tensor is used in the program so as to be able to consider the finite deformation in the process of failure. The program can not only simulate the seepage of water due to rainfall, the change of the degree of saturation, the migration of the air pressure, but also can describe the mechanical behaviors of the unsaturated soil such as the deformation of the ground, the change of pore water pressure, the formation of the shear band occurred in the slope failure on the whole in a unified way. In addition, a laboratory slope model test is simulated by the proposed soil-water-air seepage-deformation coupling FEM. By comparing with the test results, the availability of the proposed numerical method is verified.