Study On Deformation And Failure Mechanism Of Soil-Rock Mixed Bank Slope Collapse

The collapse of gravel soil slope bank is one of the most common engineering geological problems in the southwest mountainous reservoir.As a special kind of soil-rock mixture,gravel soil is more complicated than simple rock and soil.The deformation and failure mechanism of bank slope is also different from conventional rock and soil collapse.At present,there are few studies at home and abroad.so,further research is needed.This paper takes the collapse of gravel soils developed in the Pubugou reservoir of Hanyuan County,Ya'an City,Sichuan Province as examples.Based on field investigation,data collection and indoor physical and mechanical tests,the physical model test of slope control under different conditions is designed and carried out The model test restores the deformation and failure process of the gravel soil bank slope and compares it with the common bank collapse prediction method to verify the reliability of the test results.Combined with the physical model test of bank collapse,the deformation and failure mechanism of the bank slope is systematically studied.The basic evolution process and the stage of deformation and failure are summarized,which provides a certain foundation and basis for perfecting the theoretical system of bank slope collapse.This paper mainly achieved the following results:(1)The geological environmental conditions of the study area were identified.Located in the transition zone between Sichuan Basin and Qinghai-Tibet Plateau,the study area is a middle-high mountain landform with deep valleys,the tectonic movement is strong and the lithology of exposed bedrock is complicated.The main components of rocks on bank slopes are dolomite,limestone or near-source sandstone and mudstone of Sinian Dengying Formation.And the hydrogeological conditions are simple,mainly composed of bedrock fissure water and loose accumulation layer pore water,receiving atmospheric rainfall and river water supply,which are obviously affected by rainfall.(2)The developmental distribution,structural composition and deformation and failure characteristics of 23 gravel soil collapses in the area were identified.The original bank slope is divided into two types: residual type and slope-accumulated type,which correspond to two types of collapse modes: collapse retreat type and massive collapse type.At the same time,various typical bank collapse morphologies and structural elements were selected and fitted to establish a geological model of bank collapse,the slope was selected as the control factor and the water level was changed as the control condition.(3)The deformation and failure process of bank collapse under fixed water level and dynamic water level are simulated by physical model test.The deformation and failure mechanism of rock bank collapse is studied from three aspects: hydrological response law,deformation failure phenomenon and bank failure degree.The influence law and action mode of slope and water level change on bank collapse are analyzed.The basic evolution mechanism of bank collapse is summarized and the whole bank collapse is completed.The process of bank deformation and failure can be divided into three stages: local collapse,expansion and development,and ultimate stability.By comparing the width of bank collapse with the field measured values and the commonly used prediction methods,the physical model test results were verified.At the same time,the limitations of existing prediction methods for gravel soil bank collapse were analyzed.And the relevant width prediction formula was derived.