Rainfall-induced Progressive Failure Of Granite Residual Soil Slopes Based On Parameter Variation

Granitic residual soils are widely distributed in the southeastern coastal area of China.The failure of soil-like or filled slopes in granite residual soils is a frequent occurrence area of geological hazards under different environmental conditions.As a special soil,the structure of granitic residual soil by weathering is quite different,with obvious heterogeneity,the unique engineering properties of granite residual soil have caused many problems for engineers.Therefore,it is extremely important to reasonably understand the engineering geology of this type of soil Characteristics and analyse geological disasters that occur in case of human activities and environmental changes.In this paper,weathered granite residual soil in Guangdong area is selected as the research object,and a series of work is carried out from both mathematical statistics and numerical simulation.The progressive failure law of granite residual soil slopes was investigated under rainfall conditions.In the statistical analysis of the physic-mechanical parameters of weathered granite residual soil in Guangdong area,a total of 972 groups of granite residual soil samples were counted from the present tests for different engineering projects.Sampling depth and physical and mechanical parameters were included to understand the heterogeneity due to the presence of structural property.The overall statistical results from the sample show that the physical and mechanical parameters of granite residual soil are present in variability: the standard value of natural water content is 21.82%,the coefficient of variation is 0.232;the standard value of natural pore ratio is 0.796,the coefficient of variation is 0.204;the liquid limit standard The value is 31.22%,the coefficient of variation is 0.182;the standard value of the plastic limit is 19.39%,the coefficient of variation is 0.198;the standard value of the compression coefficient is 0.410MPa-1,the coefficient of variation is 0.337;the standard value of the compression modulus is4.569 MPa,the coefficient of variation is 0.253;the standard value of cohesive force is25.56 k Pa and the coefficient of variation is 0.444;the standard value of the internal friction angle is 22.96 ° and the coefficient of variation is 0.199.From a same mileage sample,due to the similarity of the parent rock,the physical and mechanical indicators of the weathering can be a certain similarity and small variability,especially in particle gradation,cohesion and internal friction angle.The porosity ratio on a weathering profile still is present in variability with the depth,however,the granite residual soil was not transported after weathering,Under the consideration of the practical engineering problems for slope failure in the Dachao highway,a two-dimensional numerical model was established to analyze slope stability and failure mode under saturated-unsaturated seepage and stress coupling.It can be noted that the porosity,dry density and permeability coefficient have obvious effects on both stability and the failure mode.The porosity ratio and permeability coefficient mainly affect the seepage field,while the dry density mainly affects the stress field.For structural soils such as granite residual soil,the distribution of the void ratio in the space cause the difference in the seepage field and stress field of slope,and then affect its stability due to a variety of failure modes.