Numerical Research On The Coupling Problem Of Seepage And Deformation In Unsaturated Soil

In the field of civil engineering production practice,whether it is the construction of foundation,slope or dam,it involves the seepage,deformation and stability of soil in complex external environment.In the field of geotechnical engineering,the analysis of multi-phase coupling evolution process of soil is an important research content in the direction of geotechnical engineering at home and abroad.The theoretical study of soil multiphase coupling is the basis of fluid seepage,soil deformation and stability,and has certain theoretical reference value for engineering practice.Based on porous medium theory and mixture theory,this paper considers unsaturated soil as a homogeneous and elastic deformable body.The evolution process of solid-water-dry gas three-phase coupling of unsaturated soil is preliminarily discussed by combining theoretical deduction,laboratory experiments and numerical simulation.The three-phase coupling mathematical model and numerical model of unsaturated soils are mainly studied,which provides theoretical guidance for the treatment of gas migration,water infiltration and soil deformation in engineering geotechnical body.The main research contents are as follows:1.A three-phase coupled mathematical model of unsaturated soils is establishedBased on the theory of porous media,the elastic-plastic constitutive model of unsaturated soil is established,and the soil is assumed to be homogeneous and isotropic.At the same time,the porous media of unsaturated soil is considered to be composed of vapor phase(dry gas,water vapor),liquid phase(liquid water,dissolved gas)and solid phase skeleton.The mass conservation equations of water,dry gas and solid skeleton are given.Based on the static equilibrium relationship,the momentum conservation equation of three-phase coupling of unsaturated soil is deduced,which lays a theoretical foundation for the follow-up numerical study.A conclusion is drawn that the three-phase components in porous media of unsaturated soil interact with each other.Finally,the method of solving the equation is introduced: Laplace transform and its properties and the numerical method of solving inverse Laplace transform.2.A numerical simulation method for three-phase coupling of unsaturated soils is presentedBased on the theory of porous media,a three-phase coupled mathematical model of water,dry gas and skeleton displacement in porous media of unsaturated soil under isothermal condition is established.Pore water pressure,pore gas pressure,soilskeleton displacement and their first derivatives are selected as state variables in solving the coupled equations.The shooting method is used for numerical simulation and analysis and the state equations in time domain are transformed into frequency domain by Laplace transform.Under given boundary conditions,the shooting method is used to solve the coupled variable coefficients nonlinear differential equations and the corresponding calculation program is developed.Based on the stabilization algorithm of Hausdorff moment problem,the numerical solution in frequency domain is transformed into time domain.Then,according to a typical case(Liakopoulos sand column drainage test),the evolution process of three-phase seepage and deformation of soil column model in drainage process is discussed.It is revealed that the pore water pressure and pore gas pressure in the unsaturated soil are constantly changing during the seepage process.At the same time,the seepage changes of water and gas phases interact and interact with each other;the migration of gas has a certain retarding effect on the drainage process of sand column;the boundary condition of gas on the side of sand column has a significant influence on the infiltration of gas.3.A finite element model of unsaturated soil slope under rainfall conditions is established.According to the conservation equations of momentum and mass,the equivalent integral weak form of the conservation equations of momentum and mass is deduced by using the equivalent integral form.A finite element model of soil slope is established to study the evolution process of rainfall infiltration,gas migration,soil deformation and slope stability of slope model under rainfall conditions.It is revealed that pore water pressure and pore air pressure in slope are interacted under rainfall conditions.Meanwhile,pore gas migration and evolution as well as soil deformation both influence pore water migration and evolution and slope stability.It is found that the numerical simulation results are in good agreement with the existing literature conclusions.The coupling effect of three-phase media in unsaturated soils is fully explained from the point of view of numerical calculation,which provides theoretical reference for the application of three-phase coupling effect in unsaturated soils.