Influence Of Moisture Content On Shear Strength Of Loess

Landslides,falls and other geo-hazards are very common in the Loess Plateau,which can bring great harm to the safety of human life and economic development.Therefore,a study of shear strength characteristics of loess and causative mechanism of loess landslides is essential.Loess is a kind of silt-silty clay,which is easily influenced by the external factors.Characterised by the large pores,vertical joints,collapsibility due to wetting,loess is a kind of problematic soil.In addition,due to the differences in physical properties,hydraulic properties and strength parameters between Loess and its underlying strata,such as weathered mudstone,alluvial red clay,loess landsliding is prone to occur under the condition of rainfall or irrigation.From the perspective of the influence of moisture on shear strength of Loess,I selected the Loess in the south of Jingyang as the main research object,the relationship between shear strength with the moisture contents has been systematically investigated based on geological survey and laboratory tests.Finally,the causative mechanism and physical of a typical loess landslide were analyzed.First,the deformation and failure characteristics of shear strength parameters were studied through direct shear tests on undisturbed loess samples with different moisture contents taken at different depth,and it can be concluded that the stress-strain behavior of the soil changed from strain softening to the strain hardening,with an increase in moisture content.Also,the increase of the normal stress renders the strain hardening of the soil more obvious.The effect of moisture content on the soil shear strength of the soil sample with low moisture content is more obvious compared with the soil sample with high moisture content.In short,the intrinsic mechanism of the weakening effect of moisture content on shear strength of loess is to weaken the cementation between the particles,rather than the friction between particles.Second,based on the of reversal direct shear tests of undisturbed soil,the residual strength has been studied.It can be concluded that at first shear failure of the Loess,the strength of the soil increases with the shear displacement,and the residual strength of the soil is controlled by the cementation between the soil particles,rather than the friction resistance of the particles.The destruction of soil can lead to a decrease in the residual cohesion,while the residual internal friction angle remains unchanged.Third,the structural strength of loess is studied by direct shear tests on soil samples,and it can be concluded that the lower the soil moisture content,the higher the structural strength;Furthermore,when the soil of strain softening behavior,the structural strength can be played.Finally,based on the field geological survey,causative mechanism and physical process of a typical high speed landslide-with long runout distance were analyzed.The failure process can be divided into tensile damage zone in the upper part,the shear damage zone in the middle part and the saturated static liquefaction zone in the lower part.