Solid-liquid-gas Three-phase Coupling Analysis Of Unsaturated Soils Based On Random Field

In practice,most of the soils are unsaturated.At present,the fluid-solid or gas-liquid coupling models are mostly used to study the seepage of unsaturated soils,but the three-phase coupling models considering both solid,liquid and gas are seldom involved.In addition,in order to facilitate the study,it is mainly aimed at homogeneous unsaturated soil.In fact,because the formation process of rock and soil is very complex,its properties often show obvious spatial variability,while the multi-field coupling analysis of unsaturated soil under the condition of considering spatial variability is more complex.To study the influence of spatial variability of unsaturated soil parameters on seepage-deformation and stability is of great theoretical significance and guiding significance for practical engineering.Based on rigorous theoretical deduction,the solid-liquid-gas three-phase coupling governing equations are obtained.The three-phase coupling model is combined with the non-Gaussian random field considering the spatial variability of geotechnical parameters.The rainfall infiltration and stability of unsaturated soils are analyzed by Monte Carlo method.The main contents and results are as follows:1)The governing equations of the solid-liquid-gas three-phase coupling of unsaturated soils are established and solved in COMSOL.The correctness and reliability of the three-phase coupling model are verified by two well-known consolidation tests of unsaturated soils.The differences between the three-phase coupling model and the two-phase coupling model are compared,and the migration of gas,the seepage of liquid,the deformation of soil skeleton and their interaction in consolidation process are explained in detail.2)The stochastic field of geotechnical parameters is discretized by the midpoint method based on Holesky decomposition and subjected to non-Gauss distribution.Combining the spatial variability theory of geotechnical parameters with the solid-liquid-gas three-phase coupling model,the rainfall infiltration problem of one-dimensional unsaturated soil column is analyzed.The effects of elastic modulus E,soil-water characteristic curve parameters(a,n)and spatial variability of saturated permeability coefficient K_s on the results were analyzed in detail by Monte Carlo method.The results show that their correlation distances and variation coefficients have little influence on the mean values of vertical displacement,pore water pressure and pore gas pressure,but have significant influence on the standard deviation.The correlation coefficients of a and K_s,n and K_s have little influence on the mean values of vertical displacement,pore water pressure and pore gas pressure,but have significant influence on the standard deviation.3)A one-dimensional three-phase coupled stochastic model is extended to two-dimensional model,and the stability of embankment is studied by strength reduction method.The influence of spatial variability of cohesion c,internal friction angle?,saturated permeability coefficient and elastic modulus on the mean value of safety factor and reliability index of embankment is analyzed.In addition,the model test of a rainfall slopen is studied,and the emptiness of K_s is discussed.The results show that the horizontal correlation distance of c and?has no effect on the mean safety factor,but the vertical correlation distance has a great influence on it,especially when the coefficient of variation is higher;the coefficient of variation and the correlation distance of K_s have an important influence on the reliability index;the distribution of the larger permeable interlayer has an important influence on the safety factor,when the larger permeable interlayer is located in the middle and lower part of the interlayer.In two-dimensional problems,the influence of K_s correlation distance and coefficient of variation on the mean and standard deviation of pore water pressure,pore pressure,horizontal displacement and vertical displacement is similar to that of one-dimensional problems,but there are also differences...