Study Of The Shear Strength On Unsaturated Loess

Loess is a special soil widely distributed in the northern region of China.Because of its large deposition thickness,and the deep groundwater level,coupled with less rainfall and strong evaporation,loess is mostly in unsaturated condition.Geological disasters occurred frequently in the loess regions.The reason is partly due to the loess itself loose structure and low strength.On the other hand,the saturation of the soil increased due to the infiltration of surface water,which affects the soil suction in the soil,causing the loess shear strength sharply reduced Sharp reduction in shear strength.The shear strength is the focus of soil mechanics.Calculation of slope stability,foundation bearing capacity and earth pressure,etc.,need the soil shear strength values.At present,Bishop’s strength theory,Fredlund’s double-variables strength theory,and Lu Ning’s suction stress strength theory are commonly accepted.Shaanxi Jingyang is a typical loess plateau area,the loess geological disasters occurred frequently in this area due to farmland irrigation.This paper,the L5 strata on the Jingyang landslide is selected as the research object.The contents and analysis of the test mainly include five aspects:(1)Through the conventional triaxial CD test,the stress-strain curves of the undisturbed and remolded loess samples under different water contents and different confining pressures were obtained,and the variation of the strength in the stage of consolidation and shearing were analyzed.Draw the stress path and strength envelope of the test process,the effective strength parameters of the undisturbed and remolded loess were calculated,and the relationship between the strength parameters and the water content can be obtained.The results show that the effective cohesion of loess decreases with the increase of water content.The cohesive decreases significantly,as water content is less than plastic limit moisture content,and then cohesive tend to be stable.The effective friction angle does not change with water content.(2)The soil water characteristic curves of loess were tested by pressure plate apparatus.Combined with the strength parameters and the matrix suction,the parameters χ and φb in Bishop’s single-variable strength theory and Fredlund’s double-variables strength theory are calculated.(3)Based on Lu Ning’s suction stress strength theory,the characteristic curves of suction stress are drawn by the conventional triaxial test results.The parameters of the suction stress are obtained by fitting the parameters of the suction stress function.(4)On the basis of the above test,the relationship between soil water characteristic curve and the relationship between shear strength and matric suction was analyzed,and a model was established to predict shear strength with SWCC.(5)The shear strength values of four strength theories under different confining pressures and suction are calculated respectively,on the three-dimensional surface map.Then propose a feasibility test method of the unsaturated loess strength parameters for engineering application.