Study On Constitutive Model And Particle Flow Simulation Of Overconsolidated Unsaturated Soil

Unsaturated soils are widely distributed in nature,and most of the soils encountered in engineering are unsaturated soils,and superconsolidated unsaturated soils are even more common,so it is of great engineering value and theoretical significance to study the properties of superconsolidated unsaturated soils.In this paper,based on the SFG model with uniform yield surface,the elastic-plastic principal structure model of superconsolidated unsaturated soil is derived by introducing uniform hardening parameters.The model is validated by comparing the calculated results with the experimental results.The model can better respond to the stress peak and shear expansion of superconsolidated soil.In order to better reflect the characteristics of unsaturated soil,gas particles are innovatively introduced and the effective stress between the matrix suction and soil particles are distinguished.The research contents and conclusions are as follows.(1)The SFG model with uniform yield surface is improved by introducing uniform hardening parameters into the SFG model with uniform yield surface,and the elastic-plastic instantonal model of superconsolidated unsaturated soil is derived.The improved model can predict the peak strength,shear expansion,softening and other properties of superconsolidated unsaturated soils,which broadens the applicability of the SFG model.The parameters of the improved model include?vp,?vp,s_sat,G,M,m,s^c,p_y0,e₀,p_yn0,s₀ and other eleven parameters,which are the same as the original model.(2)Based on the results of the derivation of the elastic-plastic intrinsic relationship,the relevant program is prepared by Matlab numerical calculation software,and the program is able to carry out the study of stress-strain characteristics of normally consolidated and superconsolidated unsaturated soil,and provide a method for the validation of the intrinsic model.(3)The desiccation test,compression rebound test,normal consolidation and superconsolidated unsaturated soil triaxial shear test were conducted on unsaturated laterite by GDS unsaturated triaxial apparatus.The experiments yielded model calculation parameters to provide data for model validation.(4)The model parameters were input into the model program to calculate the compression rebound test curves of laterite and the stress-strain characteristics of normally consolidated and supersolidified unsaturated soils,and the relationship curves of the two matched by comparing the curves of the simulation results with the test results.The model program was used to simulate some of the tests in the scholar's Rampino test,and the predicted results were compared with the original test results.The conclusion showed that the model prediction was the same as the test pattern,which verified the reliability of the model in predicting the stress-strain characteristics of the superconsolidated unsaturated soil.The model can better predict the stress-strain characteristics of normally consolidated and supersolidified unsaturated soil,such as:the peak strength of the specimen increases with the increase of matrix suction,the increase with the increase of net surrounding pressure and the stress softening phenomenon of the peak strength process of supersolidified unsaturated soil.(4)PFC3D was used to simulate the unsaturated soil consolidation and drainage test.In order to better simulate the effect of matrix suction on unsaturated soil,the matrix suction was changed by introducing gas particles and changing the number of gas particles,and the effective stresses between the matrix suction and soil particles could be distinguished.The simulation method was used to simulate the triaxial test and the direct shear test of unsaturated soil,and the simulation results were compared with the test results,and the simulation curves matched with the test curves,which verified the reasonableness of the simulation method.By observing the displacement diagram and the contact force chain diagram of the model during the simulation,we can understand the mechanism of suction force between soil particles in a simple way.