Study On Shear Volume Change And Liquefaction Characteristics Of Undisturbed Loess With Different Grain Size Components

China's loess is widely distributed,and the topography and geomorphology of the loess distribution area are complex and changeable.In addition,the impact of human production activities has caused frequent natural disasters in the loess area,seriously threatening people's lives and property,and restricting socialist modernization.Facts and researches show that liquefaction plays a crucial role in some loess landslides and foundation instability problems.The liquefaction of loess has also become a frontier topic in the field of loess mechanics research.From the perspective of liquefaction mechanism,the change of pore water pressure plays a decisive role in the generation of liquefaction,and the pore water pressure has a direct relationship with the volume of pores.Therefore,it is important to understand the change characteristics of loess under the external load and the pressure of the pore water.It has important value and significance for the study of loess liquefaction.Considering the obvious differences in the properties of different zoning loess,the original sand loess(Jingbian),silt loess(Luochuan)and sticky loess(Xiangyang)in Shaanxi Province were selected for experimental research.Based on the test of basic physical indexes,the volume change of soil during shearing was measured accurately based on GDS unsaturated triaxial apparatus,and the basic laws of shear volume change of loess with different grain sizes were analyzed.Under the premise that the initial pore ratio of the soil samples is the same,the relationship between the pore ratio of the soil samples and the pore water pressure is discussed.It is proposed to calculate the pore water pressure by using the saturated CVR line instead of the saturated CVR line.Through the experimental research and analysis,the main conclusions are as follows:(1)Jingbian sand loess exhibits strain softening during shearing and volumetric dilatancy.The Luochuan powder loess and the Fuyang clay loess showed strain hardening during the shearing process,and the volume was sheared.(2)The pore ratio of Jingbian sand loess decreased first during the shearing process,and then the pore ratio increased.As the soil sample continued to shear,the stress and pore ratio reached a fixed value.The pore ratio of Luochuan powder loess and Fuyang clay loess continued to decrease during shearing,and the volume change under low confining pressure and low water content was nearly stable,while there was no plateau in high confining pressure and high water content.(3)The CVR line of Jingbian sand loess and Luochuan powder loess is less affected bywater content,and the CVR line distribution under different water content conditions is concentrated.The higher the water content of the sticky loess in Fuyang,the lower the CVR line,and the CVR lines under different water contents are nearly parallel.(4)Based on the CVR line obtained by the unsaturated shear test,the saturated CVR line is obtained,which indicates that the Jingbian sand loess is not sensitive to liquefaction.The Luochuan powder loess and the Fuyang clay loess are sensitive to liquefaction.Finally,the pore water is calculated.This paper reveals the development law of pore water pressure caused by volume change during the process of shear deformation,which provides new research ideas and valuable exploration for studying the liquefaction of loess.