Numerical Implementation Of Unsaturated Soil MGCM And Tensile-Shear Coupling Strength Model And Its Application In Soil Slope Engineering

A large number of projects inevitably encounters slope stability problems during their construction with a continuous development of infrastructure construction in China.At the same time,most of the soil slopes are in an unsaturated state due to the influence of the groundwater level.The current instability of unsaturated soil slopes presents some main problems in strength and hydro-mechanical coupling.For example,the strength of the soil slope considers the compression-shear failure of the slope only,and ignores the effect of tensile stress on top of soil slope.However,in actual engineering,the stability of the soil slope is often affected by the tensile-shear coupling strength and the compression-shear coupling strength of the soil.The common influence of hydro-mechanical coupling is that the seepage field at a certain moment is the initial condition,then the deformation of the soil is affected by suction variation,and this is a time-dependent-pseudo-coupling calculation method.But,this method ignores the coupling between the fluid flow process and the deformation of the soil skeleton.Therefore,this paper takes an actual slope in South of China as the engineering case study.Through the self-developed interface of ABAQUS software,the hydro-mechanical coupling effect and the slope top tensile stress in the rainfall infiltration process are considered respectively to study the effect of seepage and stability of the slope.The results of the research revealed the following:(1)Based on the existing theory of hydro-mechanical full coupling(MGCM)model of unsaturated soil,the MGCM model calculation program is implemented by Fortran language,and the existing experiments are simulated.The correctness of the program was verified.Then the UMAT subroutine interface in ABAQUS software was used to extend the MGCM model to the ABAQUS software.The simulation of the dry and wet cycle test on the triaxial sample proved the rationality of the program.(2)Taking an actual slope in South of China as the engineering example,under the condition of different rainfall intensity and different rainfall duration,the extreme rainfall conditions are simulated using UMAT subroutine in accordance with the MGCM model to study evolution law of seepage field and displacement field of unsaturated soil slope.The analysis of pore pressure distribution,flow velocity vector,horizontal displacement variation and feature point data in the simulation results proves that the program can well give the variation law of seepage field inside the slope during rainfall.At the same time,the displacement field between the fluid and the soil skeleton is considered to be more realistic and effective.(3)By using the backward Euler complete implicit integration algorithm,the UMAT subroutine that conforming to the tensile strength coupling strength model was developed.It solved the problem that the traditional Mohr-Coulomb strength criterion would overestimate the tensile strength of the soil.The tensile strength of the clay is simulated to verify the correctness of the procedure.(4)According to the same slope calculation model,the simulation of slope stability is carried out by using the strength reduction factor method using the UMAT subroutine developed in accordance with the tensile-shear coupling strength criterion when considering the different rainfall durations.The numerical results show that the program can be well described for the development process of slope slip surface and slope stability under rainfall conditions.