An Investigation Of Slope Stability Considering Strength Anisotropy In Soils

Currently,researchers usually regard the soil as an isotropic medium on slope stability,that is,geomaterials show the same physical and mechanical properties in all directions.However,affected by gravity,the long axes of soil particles tend to be deposited and aligned in the horizontal direction,which will cause the soil strength to exhibit different degrees of anisotropy.In addition,when assessing slope stability according to the shear strength index tested from consolidation direction of soil,the stress state of the soil sample does not correspond to the stress distribution in actual slope,which is necessary to be studied.The dissertation starts from the anisotropic characteristics of natural soil,a strength parameter expression considering anisotropy is presented based on the microstructure theory of geomaterial.Based on the existing slope stability analysis methods(limit equilibrium method and strength reduction FEM),two specific calculation methods that consider the effect of strength anisotropy are proposed to conduct a series of studies on soil slopes.The following are main research contents and results of this dissertation:1.Anisotropic strength theory of soil is introduced in detail,and the mechanism of inherent anisotropy and stress-induced anisotropy is described.In view of the fact that the nature of slope stability is a strength problem of soil,so the influence of anisotropy on strength is highlighted.Based on fabric tensor and Mohr-Coulomb strength criterion,the anisotropic state scalar parameter A defined by predecessors is used in the dissertation,and expressions of shear strength indexes c and?considering anisotropy are proposed,and the validity and superiority of the formula's fitting effect are verified by existing test results.2.Compared with traditional Casagrande?s formula,the anisotropic strength parameter formula based on fabric tensor theory in the dissertation has more flexibility and applicability in fitting shear strength parameters with different degrees of anisotropy after selecting powers of the anisotropic state parameters_cA and A_?reasonablely.3.Anisotropic strength is introduced into the traditional limit equilibrium methods of slope stability,and the results calculated by various methods are analyzed in detail with examples.Compared with the results of existing literatures,the rationality of the proposed method in the dissertation is verified.Then the influence of slope angle,soft substratum and orientation of sediment on anisotropic slope stability is discussed.The results show that the effect of anisotropy of soil strength on the safety factor of gentle slope is greater than that of steep slope;the safety factor decreases to varying degrees after considering strength anisotropy,and different soft soil depths make the slope failure mode diverse;slopes of soil with sedimentary surface reversed are more stable than that of the slopes when it is positive.4.In order to obtain a more realistic stress field in the initial state of slope,based on finite element method,a gravity load one-time application method and a gravity load step application method are respectively adopted.After considering strength anisotropy of soil,numerical simulation is conducted to the slope model of example by strength reduction method.And the results are close to that by limit equilibrium method,which verifies the rationality of finite element method in the dissertation.5.Through detailed solution to two examples of the existing literatures,limit equilibrium method and strength reduction FEM considering strength anisotropy in soils,are respectively applied to slope stability analysis.The consistency between solution of this dissertation and existing solution is good,which further validates the rationality and effectiveness of the two methods.