Study On Wet-shear And Shear-wet Deformation Characteristics Of Unsaturated Intact Loess

Loess is a kind of soil with strong water sensitivity and special structure.In the natural sedimentary state,the intact loess has good engineering properties.However,when it meets water or the groundwater level rises,the increase of humidity in the soil will lead to a sudden change in the strength and deformation of the loess,which will lead to engineering problems such as foundation settlement and collapse.In this paper,the following tests were carried out on unsaturated intact loess:triaxial shear test under normal suction,wetting test under constant stress(equal p,equal q)and wetting microscopic test under constant stress;the soil water characteristics,deformation and strength characteristics of intact loess under two hydraulic paths of wet shear and wet shear are analyzed.Qualitative and quantitative analysis of the microstructure characteristics of intact loess after humidification under constant stress.The specific research work and conclusions of this paper are as follows:1、 The soil water characteristic curve of intact loess is obtained by unsaturated soil consolidation instrument.The variation law of triaxial shear stress-strain curve of intact loess under wet shear condition was analyzed by constant suction triaxial shear test The isotropic compression and yield characteristics of intact loess under different suction states are analyzed.The q-p critical state characteristics of intact loess under different suction states are analyzed,and it is obtained that the q-p critical state line can be approximately normalized under different suctions.2、Through the humidification test under constant stress,the soil-water characteristics of intact loess under isotropic stress and deviatoric stress are found:the influence of net confining pressure on the soil-water characteristic curve of intact loess is relatively large,and the influence of deviatoric stress on it is relatively small,and the influence of deviatoric stress decreases with the increase of net confining pressure.In the V-G model,the degassing value is a very important parameter,which reflects the strength of the interaction between soil particles and water.It is found that the degassing value increases with the increase of net confining pressure,and there is a linear relationship between them.The magnitude of deviatoric stress determines the slope of the straight line.The influence of stress state on the stress-strain curve of intact loess under shearwet condition is analyzed.The curve can be divided into two stages:loading and humidification.The relationship between the strain and the suction loss s*when the sample is humidified under constant stress is analyzed.It is concluded that the relationship between the two can be expressed by two straight lines,and the corresponding suction at the intersection is called the humidification yield suction sy.3、Through the wetting microscopic test under constant stress,the microstructure of unsaturated intact loess after shearing under different stress conditions was qualitatively and quantitatively analyzed.It was found that the microstructure characteristics of intact loess include:the skeleton particle outline is clear and the particle arrangement is loose.With the gradual increase of isotropic stress p and deviatoric stress q,the microstructure of loess changes after shear wetting,the particle contour is blurred,the small particles fill the pores,the proportion of pore area decreases gradually,and the connectivity between pores is poor,which will have a significant impact on the deformation and strength properties of soil.