Study On Rainfall Infiltration And Instability Mechanism Of Granite Weathering Crust Slope In Northern Guangdong Mountainous Area Under Heavy Rainfal

Granite strata are widely distributed in South China.Under the strong physical and chemical weathering,the exposed granite is easily weathered to form a huge granite weathering crust.The granite weathering crust shows typical binary structural characteristics,i.e.,the upper part is a loose residual soil layer and the lower part is a dense weathering rock layer,while the residual soil is easy to be softened and disintegrated by water.Theoretical significance.This paper takes the "6.12" mass landslide disaster in Mibei Village,Longchuan County,Guangdong Province,2019 as the research object,and summarizes the landslide characteristics and typical geological profile structure through on-site geological survey;designs physical model test according to the geological survey results,observes the changes of soil volume water content,pore water pressure related parameters and slope deformation and damage characteristics;finally combines the site geological survey results with the site geological survey results to observe the change of soil volume water content,pore water pressure related parameters and slope deformation and damage characteristics.Finally,numerical model is established to calculate the seepage characteristics,displacement and change of slope stability coefficient under rainfall by combining with the geological investigation data on site.The main research contents and results of this paper are as follows.(1)According to the field survey results of the landslide area,first of all,the natural geography and geological environment of the study area were elaborated,and it was clear that the stratigraphy of the study area is granite formed by Late Jurassic magma intrusion,and the stratigraphy of the landslide area is granite weathering crust,and the landslides are mostly shallow and small landslides,mostly occurring between35°～55° slope,and the sliding surfaces are all inside the residual soil layer or at the soil-rock intersection,and the damage patterns of the landslides in the area are different due to the different geomorphic characteristics and soil depth of the study area;(2)According to the current situation of the landslide area,physical models with residual layer thickness of 10 cm,20 cm and 30 cm were designed based on similar criteria.By simulating the rainfall scenario on the day of landslide occurrence,the change of volumetric water content of soil in the slope was observed and analyzed,and the law of rainwater infiltration in the slope was derived,and it was found that the difference of permeability between residual soil layer and weathered rock layer has a great influence on rainfall infiltration,and when the residual soil layer is larger than a certain thickness,strong rainfall cannot reach the surface of weathered rock layer in the whole time;(3)According to the deformation and damage characteristics of the slope during rainfall and the final damage form,combined with the change of volumetric water content and pore water pressure of the soil in the slope,the slope damage process and slope damage mechanism are analyzed,and the results are more consistent with the phenomena observed in the field;(4)Geo-studio software was used to analyze the seepage field,displacement field and stability of the slope,and the results of the analysis were compared with the physical test to verify the rainfall infiltration law and slope deformation and damage process from the physical model test;...