Research On The Stability Of Bedding Rock Slope By Repeated Mining Of Coal Seam Group

This article takes the mining of coal seam group in Sichuan province as the research background.Based on actual geological conditions,mining subsidence prediction theory,similar simulation and numerical simulation methods,the law of deformation as well as failure and instability of bedding rock slope under repeated mining conditions are studied.The stability coefficient of the slope under different working conditions is calculated based on the limit equilibrium method.This study provides a reference for the prediction and prevention of similar mining landslide disasters.The main research outcomes are as follows:(1)The calculation results of mining subsidence show that the subsidence curve of the slip surface shows an inverted S shape after mining.The curves are close to the result of numerical simulation,and the relative error is less than 7%,so it has high accuracy.(2)During the mining process,the displacement and deformation of the slope are discontinuous.The slope not only moves toward the mined-out area,but also slips toward the free face.In the single-layer mining process,only a small range of slippage occurs at the foot of the slope,and the maximum subsidence does not exceed the mining height,however,in the process of repeated mining,the slip range of the slope expanded,and the subsidence displacement of the slope surface increased significantly.The maximum subsidence reached 3.4m,which exceeded the mining height.At the same time,the horizontal displacement of the slope shoulder increases,and its maximum value exceeds twice that of single-layer mining.As the working face continues to advance to the left boundary,the displacement mutation point of the subsidence curve of the slip surface will move accordingly,and cracks will be generated near the mutation point.(3)The development of slope cracks is a dynamic process,which can be divided into temporary cracks and permanent cracks according to the different development processes.Temporary cracks are in an inverted V shape with a narrow top and a wide bottom,and permanent cracks are in a V shape with a wide top and a narrow bottom.In the process of single-layer mining,cracks develop longitudinally,and temporary cracks will occur in the middle and lower parts of the slope,the development process of the cracks include three stages: accumulation of deformation,crack development,and shrink to closed.Permanent cracks occur on the upper part and top of the slope,the development process of the cracks include accumulation of deformation,crack development,and deformed to stable.Affected by repeated mining,horizontal cracks increased,and old cracks tend to develop again.At the same time,some temporary cracks eventually transform into permanent cracks.The width and depth of cracks do not increase simultaneously.In the middle and early stages of repeated mining,the depth of the cracks increases significantly,while in the later stage of mining,the width of the cracks increases significantly.The slope stress near the cracks fluctuates drastically,and the stress just below the cracks is unloaded,the stress on both sides of the crack shows an opposite trend.Under the influence of repeated mining,the stress fluctuation range of the slope body expands,the vertical stress increases,and the damage phenomenon is obvious.Part of the cracks developed to the slippery surface,and the fractured slopes are formed sequentially from bottom to top,providing favorable conditions for rainfall infiltration.(4)Under natural conditions,the fractured slope will not produce landslides.Under full rainfall conditions,the cohesive(friction angle)of the sliding surface is reduced from 0.221(14.923°)MPa to 0.143 MPa(10.104°).The softening coefficient q is defined as the ratio of the mechanical parameters of the sliding surface after rainfall to the mechanical parameters in the natural state.therefore,the q value decays continuously from 1 to 0.66(the slippery surface reaches the saturated state).The slope stability coefficient is linearly positively correlated with the q value,and negatively correlated with the water-filled depth of the crack.As the water-filled depth of the crack increases,the sliding surface gradually reaches a saturated state,and the stability of the fractured slope continues to decline.Eventually,the traction landslide will occur from bottom to top along the sliding surface.