Progressive Failure Research Of Residual Soil Slope Based On The Shearing Strength Weakening Effect

There is granite residual soil slope widely distributing in the coastal area of Southeast China.Due to the structural nature of granite residual soil as well as the climatic characteristics of the rainy season,slope progressive failure even landslide was usually caused by high intensity and long-time rainfall.In the gradual failure process,the dynamic change course of the shear strength parameter of residual soil can be a key factor causing slope failures.Therefore,it makes sense to study on the attenuation law of shear strength parameter and the stability change regulation for preventing this kind of landslide disaster.In the dissertation,based on a gravelly granite residual soil slope,the research on progressive failure and stability of the residual soil slope under rainfall was carried out by means of on-site soil sample collection,laboratory test and model test,and finite element numerical calculation.The chief work carried out and results as follows:(1)Study on the microstructure of granite residual soil before and after rainfall as well as the changing of shear strength mechanism.The results showed that:the microstructure of undisturbed soils samples presented as polymeric structure,but the blowup revealed cataphracted cataphractus clearly and dense microstructure.From an overall perspective,the soil was no particular order while partly got directional alignment.However,the sheet and aerial construction was clearly visible in the wringing soil samples and the blowup showed the surface skin was upwarping and even peeling off,this was the weak layer.The diversity of microstructure between undisturbed soils samples and wringing soil samples determined the weakness property of residual soil.(2)Study on the the influence of the moisture content on granite residual soil shear strength parameter.The study found that,the cohesive force decreased obviously with the water content increased while the internal friction angle was less obvious.Furthermore,the decaying-degree was weaker when moisture content was not so big.The degenerative cumulant of cohesive force remained higher than internal friction angle,and that slope of decay curve almost keeped unchanged while the internal friction angles' gone through slow-growth then gradually move on to greater increases.(3)Residual strength characteristic study of residual soil.Results of the trial indicated that,when residual cohesive force close to zero,the residual angle of internal friction remained larger value.This is the feature of residual soil and also the essence of developed strength in the case of large deformation at the same time.(4)Study on the rules that water content responsed to rain in residual soil slope test.Experimental results showed that the response time of topsoil was the shortest and has bimodal characteristics in the time-varying curve of water content.The response time of deep layer would take longer and the growth rate presented biger in the earlier stage than the later,and that time-varying curve presented serrated and flat.(5)Model test on the progressive stability of slope based on the gradually-changed shear strength.The result showed that:the first step of slope failure was the local slide of toe area while the shear strength was changing by water content.Subsequently,a new slip surface come into being gradually at the free face which is formed due to the slump of slope toe and shoulder.The process revealed that soil in different zone can offer different shear strength during the progressive failure process.