Numerical Analysis On Coupled Solid–Liquid–Air Of Unsaturated Accumulation Soil Slope Due To Rainfall

The seepage, deformation and stability of unsaturated soil slope induced by rainfall are important issues that have been studied in geotechnical engineering. It will transcend the classical soil mechanics to study the problems based on the multi-field coupling theory, and obtain new understandings. In addition it will also help better understanding rainfall-induced soil slope failure. It has important significance to geotechnical theory research and engineering applications.This paper takes the loose accumulation soil in Southwest China as research object, and studies the SWCCs(Soil-Water Characteristic Curves) under the creep conditions using the pressure plate apparatus. The effects of different factors on the SWCCs and compression creep are analyzed. The coupled solid–liquid–air model is established and calculated using the finite element software COMSOL. The seepage, air migration, deformation and stability of unsaturated soil slope under the conditions of rainfall have been studied, and it is also applied to the engineering projects. The main research contents and achievements are as follows:(1) The SWCCs under the compression creep are tested using the pressure plate apparatus. The compression creep curves and SWCCs under different axial compressions, initial moisture contents and initial dry densities are obtained. The effects of compression creep on the SWCCs are analyzed. The compression creep curves and SWCCs with different conditions are discussed. The test results show that soil deformation casued by compression creep are proportional to the maximum axial pressure and initial moisture content, and inversely proportional to the initial dry density. The soil with larger axial pressure and higher initial dry density have higher storage capacity and larger air entry value.(2) The coupled solid–liquid–air model is established based on continuum mechanics and mixture theory. The finite element software COMSOL is used to calculate and verify the reliability of three-phase coupling model based on the test results of sand column. The differences among three-phase coupling model, fluid-solid coupling model and air-liquid coupling model are compared. The blocking effects of the pore air and soil deformation on infiltration into unsaturated soils are revealed.(3) The water seepage, air migration, deformation and stability of soil slope under the rainfall conditions are studied. The delaying effect of the wetting front caused by the migration of pore air and the deformation of soils are discovered. The influence of rainfall durations, entry values and the anisotropy on the seepage and stability of unsaturated soil slope are discussed. The analysis shows that the change of pore-air pressure is related to the depth of the soil, the aggregation and dissipation of pore pressure in deep buried soils relatively lag. The pore-water pressure and deformation in the fluid-solid and air-liquid models change faster than the solid–liquid–air model when the blocking effect are not considered. The anisotropic conditions are related to depth and position of the unsaturated soil slope.(4) Based on the previous studies, the coupled solid–liquid–air model is applied to the practical case. The variation of displacement, pore-water pressure, pore-air pressure, and stability are analyzed. The maximum total displacement can fit well with the actual sliding surface. The results indicate that the coupled solid–liquid–air model can be well applied to practical engineering.