Experimental Study Of Unsaturated Red Clay Shear Strength

Rainfall infiltration and reservoir water level fluctuation are one of the main causes of bank landslide instability.The effect of water on slope stability is mainly reflected in the load effect on the slope body and the softening effect on the material strength.At present,the theory of load effect is already mature in theory,but in the softening effect of material strength,due to the close correlation with the characteristics of the soil itself,it is necessary to study the specific soil type in the actual project.Therefore,this project is based on the need to evaluate the slope stability of the Tanjiahe landslide in the Three Gorges reservoir area under the effects of rainfall infiltration and reservoir water level,and a series of experimental tests have been conducted on the shear strength characteristics of red clay.1)A set of shear strength test methods suitable for this test was obtained through experimental exploration.Combining the triaxial test and the direct shear test,the red loam soil was tested and studied.Based on the needs of the experiment,some of the instruments were improved and the sample preparation method was optimized to improve the reliability of the test data.2)The effects of saturation and density change on the stress-strain relationship of red loam were studied.The results show that the stress-strain curve of the red loam is significantly affected by saturation and compactness,and the change of saturation is more obvious than that of the stress-strain curve.With the decrease of saturation,the stress strain curve of the red loam is gradually changed from hardening to softening,and the more dense the soil is,the more obvious the transformation is.3)The triaxial test of red clay under different saturation and density conditions was carried out,and the curve of shear strength with saturation and density was obtained.The test results show that the soil shear strength index decreases with the increase of saturation,and increases with the increase of density,and is affected by the saturation,and is affected by the compactness relatively small.Based on the least-squares method,the cohesion force,internal friction angle and saturation correlation were fitted.It was found that the cohesion force,internal friction angle and saturation had a good exponential relationship.4)Based on the theory of total stress strength of unsaturated soils and the test data of shear strength of red clay under different saturation and density conditions,a shear strength model of red clay considering the effects of saturation and compactness was deduced.The analysis shows that this model can better consider the effects of saturation and compactness on the cohesion and internal friction angle of soil.5)Combined with the above results,by using the finite element method to simulate the seepage field in the rainfall infiltration process,and combining the established shear strength model of red clay,the residual thrust method is used to calculate the safety factor of the material strength of the slope without considering the change of the slope body saturation with the slope body saturation,and the process of rainfall infiltration in the tanjiahe landslide is analyzed.The evolution law of the stability of the middle slope.The results show that in the process of rainfall infiltration,it is conservative to evaluate the slope stability without considering the change of the material strength of the slope itself with the change of the saturation of the slope.