The Study Of Deformation And Damage Mechanism Of The Bedrock Landslide Under Underground Mining

Based on the case study of the Shanyang landslide in Shaanxi Province,this study aims to analyze the characteristics of landslide deformation and destruction and evaluate the corresponding influential factors.The study was performed through field work,laboratory tests,and numerical simulation.At field work stage,the topographic measurement and lithological investigation on and around the landslide have been made to reconstruct the pre-event topography and the underground structures,by which the topographic input for numerical models were derived.At the laboratory stage,the shear strength tests on the major structural planes of the collapsed rock mass have been carried out using the direct shear apparatus for large-scale rock mass,by which the geotechnical input for numerical simulation were derived.At the modelling stage,two different numerical models have been applied,the two-dimensional Discontinuous Deformation Analysis(DDA)model and the Sassa model.The former was used to simulate the stress and displacement fields at landslide body and top locations under the influence of undermining activities.The latter was used to simulate the sliding process of the whole landslide.From these two models,the landslide initiation mechanism and movement were analyzed,respectively.According to above four stages,the corresponding results indicate the facts as follows:(1)Shanyang landslide belongs to the bedrock landslide.The landslide is mainly triggered by a long-term exploitation of vanadium ore,combining with the characteristics of the local geomorphological and geotectonic features.(2)Landslide parameters in the study area were obtained through geological survey,sampling,measurement of roughness and occurrence of rock mass.The relevant parameters of landslide bedrock,slipping zones,and landslide body were obtained by the conventional laboratory tests such as gravity test,point load test,direct shear test of rock,etc.The uniaxial compressive strength and uniaxial tensile strength of rock were calculated by point load test,and the rock cohesive c and internal friction angle ? of the main structural plane were obtained by Barton method.Moreover,the parameters of slipping zones can be replaced by the parameters of c and ? of the first structural plane.(3)The DDA simulations were carried out for back-analysis of three different engineering operation modes: the unexcavated mode,the semi-excavation mode in the middle part,and the fully excavated mode in the middle part.Then based on two different mining plans,the fully excavation modes for the upper part and the lower part of the slope were developed for forward-analysis.From the results of back-analysis,it was concluded that the slope failure caused by underground mining can be divided into three stages: the stage of collapse of goaf caused by underground mining,the stage of complete collapse of goaf and crack formation on the trailing edge of the slope,the stage of formation of the landslide.From the forward-analysis,it has been found that the mining location has a significant effect on slope stability.The upper mining is favorable to the slope stability,however,the middle and lower mining have an opposite impact,which is unfavorable to the slope stability.(4)The Sassa model predicted that during the sliding process,the main direction of the landslide experienced two changes until the sliding halts,which is coincide with the actual landslide slip process.According to the speed analysis of sliding process,three phases have been simulated,accelerating phase,fluctuating phase,and decelerating phase.