Constitutive Equation Of Stress-strain-strength Characteristics Of Unsaturated Jingmen Expansive Soil

The stress-strain-strength characteristics of unsaturated expansive soil are complex,so it is of great theoretical significance and application value to carry out systematic constitutive simulation for shallow surface expansive soil engineering.Based on BBM and Sun De’an model,constitutive simulation of stress-strain-strength behavior of Jingmen expansive soil is carried out in this paper.According to the saturation/unsaturated strength/deformation test results,BBM and Sun De’an model parameters were calibrated.Based on the calibrated model parameters,the constitutive simulation of the saturated/unsaturated one-dimensional compression-unloading,dry shrinkage,wet swelling and three-dimensional stress-strain-strength behavior of Jingmen expansive soil was carried out,and the applicability and effectiveness of the BBM and Sun De’an models to describe the stress-strain-strength behavior of Jingmen expansive soil was discussed.This paper tries to provide more reasonable model parameters for finite element numerical simulation of shallow surface expansive soil engineering.The conclusion is as follows:(1)Twelve complete parameters of Jingmen expansive soil model were calibrated based on BBM.The reproduction results show that:BBM can better describe the Jingmen expansive soil saturated/unsaturated unsaturated compression and the behaviour of volume swelling while unloading,wet swelling,and the strength behavior under the three-dimensional stress state.In addition,BBM can well describe the dry shrinkage behavior of Jingmen expansive soil,but it is difficult to describe the constant volume of soil after shrinkage.(2)Nine complete parameters of Jingmen expansive soil model were calibrated based on Sun De’an model.The reconstructed results show that:the Sun De’an model can better describe the saturated/unsaturated state of compression,the unloading volumetric expanding and the three dimensional stress state of strength and deformation behavior.Especially before the axial strain is less than 15%,the model prediction of Jingmen expansive soil deviatoric stress-axial strain,volumetric strain-axial strain relationship is quite consistent with the test result.(3)The comparative analysis between BBM and Sun De’an model shows that:(1)BBM choose suction as the stress variable;Sun De’an model takes the suction stress as the stress variable and suggests the relation between the suction stress and suction force.(2)There are twelve parameters in BBM and nine parameters in Sun De’an model.The parametersλ_s andκ_s in BBM can describe the behavior of wet swelling and dry shrinkage under constant net stress,but there are no related parameters in Sun De’an model.(3)The compression index of BBM decreases with the increase of suction;In the Sun De’an model,the compression index increases with increasing suction.(4)BBM adopts non-correlated flow law and Sun De’an model adopts correlated flow law,resulting in differences in volumetric strain formulas.(5)Both model can effectively describe unsaturated stress-strain and strength properties of Jingmen expansive soil,BBM reproduction ability better than Sun De’an model.