Improvement And Verifition Of The SFG Elasto-plastic Constitutive Model For Unsaturated Soil

Because the soil is affected by the natural environment such as temperature and atmospheric rainfall in its natural state,its saturation is often in a state of change,which causes the ratio of solid,liquid and gas three-phase substances that constitute the soil in the natural state is not constant.The soil will deform during saturation humidification or drying.Soil moisture is an important cause of a series of serious engineering accidents such as foundation settlement,slope instability,and roadbed subsidence.In order to find a safer,more economical and reliable way to prevent or deal with various engineering accidents caused by changes in saturation in the foundation soil due to saturation,the first work to be done is to deeply understand the law of the stress deformation phenomenon of unsaturated soils with saturation.Therefore,the study of the elasto-plastic constitutive model of unsaturated soil has far-reaching significance for preventing or dealing with engineering accidents caused by changes in saturation of soil.In this paper,the yield surface of the SFG model is improved,and then the corresponding elastoplastic constitutive relation is derived.The model calculation process is programmed using a computer language.Determine the calculation parameters required for model simulation by completing the test.Enter parameters into the model program for calculation.The calculated results were compared with the unsaturated triaxial test data.Verification model simulates the correctness of stress-strain behavior of unsaturated soils.The specific work content is as follows:?1?In this paper,the method of uniform yield surface is introduced into the loading collapse yield surface of SFG model,and a new yield surface is obtained.The new yield surface has smooth continuity,which has the characteristics of the loaded collapse yield surface?LC yield surface?in the SFG model,and can also reflect the characteristics of the suction increase surface?SI yield surface?proposed in the BBM model.Based on the improvement of yield surface and elasto-plastic theoretical framework,the corresponding elasto-plastic constitutive relations are derived.The improved model overcomes the problem in the original model,the LC yield surface alone cannot describe that the suction is greater than the critical saturation suction value Ssat and the suction increases to produce plastic deformation.It also simplifies the coupling analysis of the yield surface in the double yield surface model and broadens the applicability of the SFG model.?2?Derivation results based on elastoplastic constitutive relation expression.The model calculation process is programmed using a computer language in Matlab numerical calculation software platform.Provides a convenient method for verification calculation of model reliability.?3?Model parameters determination of red clay in a certain area of Nanchang using unsaturated soil consolidation direct shear device.Determined eleven parameters required for model calculation.The eleven parameters including the?_vp??_vp?s_sat?G?M?m?s^c?e₀?p_y0?p_yn0?s₀ are obtained.Provides data protection for model validation.?4?The experimental results show that the compression springback coefficient of red soil samples in a certain area of Nanchang varies with the matric suction.Compare the parameter law obtained from the experiment with the parameter law predicted by the model.The two are consistent.The feasibility of SFG model to simulate the stress-strain behavior of laterite in unsaturated state is proved.?5?Entering the red clay calculation parameters obtained from the test into the program to obtain the calculation result.Using program to simulate the strain behavior of soil samples under unsaturated conditions under various stress paths.The calculated stress-strain relationship curve is compared with the stress-strain curve obtained by the members of the research group on the unsaturated triaxial test of laterite.The two are consistent.Using the model program to simulate the unsaturated triaxial test of remolded silty clay by Cunningham et al.And compare the calculation results with the test results in the published literature.The two are consistent.The reliability of the model for stress-strain behavior simulation of unsaturated soils is verified.