Mechanism And Prediction Model Of Overlying Strata Movement And Deformation Based On The Stress Distribution

Mining opreations not only influences stability of the structure(chambers,tunnels,shafts etc.),but also induces mining-induced fracture in overlying strata.Water inrush accidents occur frequently once the mining-induced fracture connects the surface and subsurface water bodies.Moreover,mining-induced fracture around the goaf is the channel for gas accumulation,which is a threat to simultaneous exploitation of coal and gas.All the above mining problems are related to the movement and deformation of rock mass.Therefore,study on mechanism and prediction model of overlying strata movement and deformation has theoretical value and practical significance.Based on numerical simulation and a large number of measured data in situ,theoretical analysis and engineering practice method,this study obtained the following achievement:the stress and displacement characteristics of mining-induced overlying strata,deformation mechanism of rock mass in overlying strata,the dynamic movement and deformation characteristics and prediction model of surface and subsurface,and the calculation method of fracture development based on movement and deformation of overlying strata.The main results and innovations are as follows:(1)Based on abutment pressure distribution variation around working face,abutment pressure distribution function of overlying strata was established.Distribution characteristics of abutment pressure distribution around working face and overlying strata was obtained by numerical simulation and theoretical analysis,meanwhile,the function between the abutment pressure function of the horizontal rock stratum under different buried depth was established.According to the load conservation principle of working face and overlying strata,the variation characteristics of the parameters of stress recovery function of rock strata under different buried depths was derived,and we found the farther the strata was from the coal seam,the faster the stress recovered.The variation of movement and damage of overlying strata was obtained by comparing the strata subsidence curve under different buried depths and plastic region during mining.(2)Deflection differential equation of rock mechanics model was established using the elastic plate theory.Taking the basic roof as a study object,the author got the solution and verified the model.The model parameters and the variation of the flexural curve of the strata with different depths were analyzed,and the internal movement and deformation mechanism of overlying strata was revealed.(3)Based on the data of surface movement observation in Peigou Mine,dynamic features of surface movement and deformation was studied to obtain the variation of the maximum subsidence velocity and its lag distance on the major cross-section during working face advancing.The prediction formula of the maximum subsidence velocity on the major cross-section of subsidence basin was derived by the function of the subsidence velocity curve.Based on the relationship between the dynamic deformation parameters of the surface and overlying strata,the prediction model of the dynamic movement and deformation of surface and overlying strata at any mining time was established.(4)The study analyzed the mechanics principle and the characteristic of movement and deformation in overlying strata,and found the flexural rigidity of overlying strata was the main factor related to the major influence radius of overlying strata.The formula for calculating major influence radius was obtained based on the variation characteristic of the flexural rigidity of overlying strata.Based on measured data in situ and numerical simulation results,the influence index of the subsidence coefficient and offset of inflection point were obtained with the curve fitting method,the prediction model with the function of modifying expected parameter of movement and deformation in overlying strata was presented.The prediction model could reflect the variation characteristic in overlying strata with the change of measured parameters of surface,and the model has a good forecast ability and operability,considering that it's predicted parameters were based on the surface measured data in situ.(5)By analyzing the features of mining-induced fracture in overlying strata,interlayer tension rate and bedding layer tensile rate of overlying strata were used to represent the development degree of interlayer fracture and vertical penetrating fracture respectively.The distribution characteristic of interlayer tension rate and bedding layer tensile rate in overlying strata of Peigou working face mining was is obtained by overlying strata movement and deformation computational model.According to the field measured height of the water-flow fractured zone,the movement and deformation index of fractured water transmissibility was obtained by inversion,namely critical value of bedding layer tensile rate(?'_S)is 0.28%.Then the author put forward the calculation method of mining-induced fracture development of movement and deformation in overlying strata.With calculation of overlying strata movement and deformation of the different mining scheme,the distribution characteristic of mining-induced fracture in overlying strata and development height of water-flow fractured zone was obtained with different mining width along the dip of coal seam.Finally,the influence factors of water-flow fractured zone are analyzed.All the research results above could provide reference to control of coal mine water bursting and gas extraction in mining-induced fracture zone.