| The bedding rock slope is a common and special landform in the southwest mountainous area.Mining under bedding rock slope is prone to the occurrence of geological hazards of bedding landslide,which is often large-scale,harmful and serious.Therefore,the study of deformation and failure mechanism of bedding slope after mining has important theoretical significance and practical value for safety production,geological hazard prevention,and ecological environment management.In this paper,the combination of field measurement,indoor rock mechanics experiment,similar simulation test,numerical simulation analysis,and theoretical analysis is used to study the deformation and failure characteristics of bedding rock slope under the influence of different mining procedures.And a similar simulation test method for mining under bedding rock slopes is put forward.A similar simulation test method for the slope-sliding surface was developed.Then,a similar simulation test device for mining under bedding rock slope is developed.Afterward,a similar simulation test of the mining bedding rock slope is carried out.It contributes to revealing the formation process,mode,and mechanism of deformation and failure of bedding rock slope caused by mining.On this basis,the fault prediction model of bedding rock slope after mining is established,and the stability analysis method of fault slope is proposed.The prediction model and stability analysis method are applied to the analysis of mining under bedding rock landslide.Through the above research,the main conclusions and results are obtained as follows:(1)Two methods,bottom friction simulation test and numerical simulation analysis are adopted to deal with the slowly inclined single coal seam by longwall mining method.And the goaf is treated by full subsidence method.Then,the deformation and failure response of mining under bedding rock slope is studied through four mining procedures in section,including single-section mining,leaping mining,downward mining(mining along the slope),and upward mining(mining against the slope).The results show: different underground mining procedures form results in different position relations between slopes and goaves,which lead to different degrees of deformation and destruction in slopes.But in the four types of mining procedures,the rock mass is unloaded and deformed in the direction of goaf.Bending and tension failure occurs in all strata and plastic deformation occurs in weak interbeds,resulting in tension cracking,fracture and slip failure.Afterward,deformation and failure of overlying strata in goaf all form caving zone,fissure zone and bending subsidence zone.And the surface slope is located in the upper part of the bending subsidence zone,and its damage scale and degree are mainly controlled by geological environment and mining procedure.There are two kinds of cracks in the bedding rock slope body under the influence of mining,which is the upper opening and the lower opening.The upper opening cracks occur at the boundary of mining influence area,mainly due to the tensile deformation of slope surface;while the lower opening fracture occurs in the middle of the mining influence area,which is mainly caused by the movement of rock mass and surface to the goaf under the influence of mining.After four mining procedures,the subsidence curves of weak intercalation(potential slip surface)in the main section inclined to be four sharps of "concave","convex","S" and "anti-S",respectively.Among the four mining procedures,the deformation and failure of bedding rock slope induced by mining against the slope are the most serious,and the risk of instability and landslide is the greatest.(2)Deformation and failure characteristics of mining under bedding rock slope are that mountain slope body can be studied as a plane.The bedding rock slopes in the southwestern mountainous area are mainly composed of thick layered sedimentary rocks with weak structural layers.The deformation and strength characteristics of these slopes are controlled by the combination of layers and rock layers,thus the stability of them is poor.The unstable structure may cause slippage,especially bending failure of rock formation and plastic deformation of weak rock formation.The fractures are often seen on the surface of bedding rock slopes after mining.Their size and distribution are related to geological conditions,mining conditions,goaf scope,and micro-geomorphology.The maximum subsidence value of movement and deformation of the bedding rock slope may be larger than mining thickness,and the maximum horizontal movement may also be larger than the maximum subsidence value.The maximum value of other deformation in this condition may be larger than that in the plain area.The bedding landslide is the most serious discontinuous sliding failure in deformation and movement of the bedding rock slope after mining.Under the influence of mining,mining slip is generally inevitable,but the bedding landslide after mining is not always happened in all cases.(3)The geological and mining data of the study area are collected,and the basic characteristics of bedding rock landslides in this area are investigated and analyzed.The ground movement caused by mining in another working face(No.4113)of the same rock seam in the same mine is measured in situ,and the ground subsidence data and rock movement parameters are obtained.The measured data verify the validity of the established numerical model(field equation,boundary condition,material parameters,etc.).It is feasible to use this numerical model to analyze the bedding rock landslide after mining.(4)Similar simulation test method of mining bedding rock slope with variable slip surface is put forward,and similar simulation test device of mining under bedding rock slope with variable slip surface is developed independently.Under different mining procedures,the test device can simulate the deformation,failure,and stability of bedding rock slopes with weak interbeds widely distributed in southwestern mountainous areas.In essence,by changing the boundary conditions of the lower part of the model(sliding surface),the stress distribution of the sliding surface and the sliding body can be changed,resulting in the failure of the sliding body.Furthermore,coupled with the physical and mechanical action of water,the sliding body becomes unstable and forms a landslide.The device indirectly simulates the influence of underground mining on a slope with the use of high-strength rubber sheet,which greatly saves the number of similar materials used for preparing and filling bedrock,mining stratum,and other soft interbedded rock layers.Also,it shortens the model stacking time and reduces the workload.(5)The deformation,failure,and instability of bedding rock slope induced by the mining against the slope mining in No.1112 working face and lower ones are studied by numerical simulation analysis and similarity simulation test.The results of numerical simulation and similar simulation are basically similar.The results show that the bedding rock slope affected by upstream mining is in the form of "cantilever beam",and fracture occurs with mining.With mining,the fracture failure occurs,and the fracture slope falls on the weak interlayer,which shows the cantilever-fracture failure mode.Considering the influence of water,the deformation,failure,and instability of the model slope are basically the same as that of the prototype landslide,which is the bedding rock landslide of the initial traction type and the later pushing type.Similar simulation test reflects the process of deformation,failure,and instability of prototype under the influence of underground mining.(6)After mining against the slope,the movement of overlying strata above goaf develops from the bottom to the top and from inside to outside.For bedding rock slopes with outward dipping and weak interlayer structure,after underground mining,the first step is the subsidence and deformation of weak interlayer(potential slip surface)and its underlying strata(sliding bed).If the strength,elastic modulus,and integrity of bedding rock slope(potential sliding body)are higher than those of the underlying strata of weak interbedded rock,the deformation of bedding rock slope will not synchronize to produce separation layer.When the weak interlayer bends and sinks,the upper slope can be regarded as a cantilever beam.Once the cantilever beam cannot withstand its own gravity,bending fracture occurs on the slope.The formation and development process of deformation and failure of bedding rock slope after mining is as follows: separated movement between the slope body and its lower strata ? occurrence of the separation(weak interlayer or contact surface of the strata)? bending of slope body under gravity ? overhanging of strata of slope body ? tension fracture of slope surface ? fracture failure of slope collapse.The deformation and failure mode of bedding rock slope induced by mining against the slope is cantilever-fracture mode.The evolution process of deformation and failure of bedding rock slope after mining can be divided into three stages: mining subsidence cantilever,failure of the slope and instability of the sliding slope.(7)Based on the theory of elastic foundation beam,the bedding rock slope with weak structural layer is treated as the research object.The rheological medium constitutive model is used to derive the basic equations of stress and bending moment of bedding rock slope after mining.The prediction model of bedding rock slope after mining is established,and the prediction of the location and distribution of surface cracks in the bedding rock slope is realized.Considering the weakening of the mining and the softening of the water,the weakening phenomenon and the weakening coefficient are defined.Based on the Moore Coulomb strength theory,the limit analysis method is used to analyze the stability of the bedding rock slope under natural state and saturated state.(8)Based on the analysis of the basic characteristics of the bedding rock landslide in the study area,the fracture prediction of the actual prototype and the similar model is carried out.Also,the stability analysis of the fracture block is realized.The results from actual prototype slope theory show that the predicted crack(back edge)is at the position of 113.36 m from the toe of the slope,and the length of the measured slide is 114 m.The error is only 0.46 m and the relative error is 0.56%.The prediction effect of the model on the fracture failure is good.The results of the similar model show that the prediction results have an error of 0.0228 m and the relative error of the similar model is 6.12%,which indicates that the similar simulation test can reflect the actual situation of the mine.The fracture stability analysis of the prototype slope shows that when the physical and chemical effects of mining damage and surface precipitation are the same,the deeper the water-filling depth of the cracking crack is,and the smaller the stability coefficient of the fractured slope is,the fractured slope is more likely to be unstable.This process is consistent with the actual phenomenon of the landslide.The fracture stability analysis of the similar model shows that the fracture slope is stable after mining.But surface precipitation continuously weakens the mechanical strength of the weak interlayer through cracks.When the strength of weak interlayer is weakened by 0.34 times,the fractured slope A reaches the state of imminent sliding,resulting in the landslide.After the fractured slope B loses the skid resistance of the fractured slope A,it also immediately produces slip.This process is consistent with similar simulation process. |
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