Study On Liquefaction Evaluation Method Of Sandy Loess Based On Variation Characteristics Of Unsaturated Shear Volume

Due to its unique geological environment and the special structure of loess,coupled with the influence of natural factors and human activities,the loess landslides and foundation settlements caused by liquefaction frequently occur in the loess area,which seriously endangers people's lives and property safety.From the perspective of the mechanism of liquefaction,liquefaction is the result of the continuous accumulation of pore water pressure of the shear-shrinkable soil under the condition of poor drainage.Therefore,to understand the mechanism of liquefaction,we must first analyze the shear deformation characteristics of the excavated soil.In the research of loess liquefaction,many scholars directly measure the pore water pressure through the saturated loess test to evaluate the liquefaction sensitivity of loess.However,the original structure of the loess sample is usually destroyed during the loess saturation test.Therefore,it has important theoretical and practical significance to study the liquefaction of saturated loess by studying the shear deformation characteristics of unsaturated loess under external load.This paper takes Gansu Gulang sandy loess as the research object,based on the unsaturated triaxial shear test,analyzes the development law of sandy loess volume change under different water content and confining pressure conditions.At the same time,in order to eliminate the constraints of specific instruments in the triaxial shear test and the influence of system errors and membrane embedding on the shear variables during the test,the particle flow numerical simulation technology is introduced to perform numerical simulation on the loess indoor triaxial test.Study the basic law of sandy loess shear volume change under different water content and confining pressure.On this basis,the critical state line obtained by the shear body of unsaturated sandy loess under different water content is used to fit the saturated approximate critical state line of the sample.Comparing it with the critical state line directly obtained from the saturated loess consolidation and undrainage test,a liquefaction evaluation method based on the deformation characteristics of unsaturated shear volume is proposed and the application of the liquefaction evaluation of the Gulang sandy loess is proposed.The main results of the thesis are as follows:(1)Through triaxial shear test and particle flow simulation,it is concluded that the stress-strain relationship curve of Gulang sandy loess is strain "hardened" type,and the shear deformation is of shear shrinkage type.Under low confining pressure and low water content The joint action is strain "softening" type,and the deformation of the shear body is shown as a dilatancy type.(2)The slope of the critical state line of sandy loess based on the formation of unsaturated shear bodies is less affected by the water content,and the critical state lines of different water content are approximately parallel.Under the same confining pressure,the higher the water content of sandy loess,the smaller the void ratio when reaching the critical state,and the lower the critical state line.(3)The saturated approximate critical state line of the sample can be fitted by using the critical state line at different water content,and then the saturated approximate critical state line fitted based on the critical state line of unsaturated sandy loess can be directly used in the undrained test of saturated loess.The obtained critical state line is compared and analyzed.A liquefaction evaluation method based on the deformation characteristics of unsaturated shear volume is proposed.(4)The liquefaction evaluation of Gulang sandy loess was carried out by applying the proposed liquefaction evaluation method.