A FE analysis on slope failure in unsaturated ground based on soil-water-air fully coupling theory

In this paper, a program of Finite Element Method (FEM) named as SOFT, using Finite Element-Finite Difference Scheme (FE-FD) for soil-water-air three-phase coupling problem, has been developed based on a rational and simple constitutive model for unsaturated soil proposed by Zhang and Ikariya (2011). The model can properly take into consideration the Moisture Characteristics Curve (MCC) of unsaturated soils. In the program, the FE-FD formulation in saturated condition of soil-water coupling problem, proposed by Oka et al. (1994), has been extended to unsaturated condition in soil-water-air fully coupling scheme. In order to verify the availability of the proposed numerical method, triaxial tests on unsaturated silty clay under fully undrained and unexhausted conditions, conducted by Oka et al. (2010), are firstly simulated by the proposed method. The development of pore air pressure and pore water pressure measured in the specimen can be well reproduced by the proposed method. Furthermore, model tests on slope failure in unsaturated Shirasu soil, carried out by Kitamura et al. (2007), are also simulated by the same numerical method. From the simulation it is known that the slope failure behavior of the model ground observed in the tests can be described in a satisfactory accuracy on the whole.