Damage Characteristics And Permeability Evolution Laws Of Strata On Stope Boundary

During longwall mining,the overburden is damaged seriously and the fracture is highly developed and hard to be compacted and closed on stope boundary,which is the high risk area for water loss induced by mining.Based on the subject of damage characteristics and permeability evolution laws of the strata on stope boundary,theoretical analysis,numerical simulation,field measurement and laboratory experiment are adopted to study on the scientific problems of stress distribution,fracture development and permeability evolution of overburden above coal pillar under the overlapping of mining inducement in both sides of stope boundary-affected area.The main research results are as follows:(1)According to the characteristics of stress distribution,the stope boundary-affected area was divided into two parts: the area effected by solid coal and the cover stress re-establishment area.Based on the limit equilibrium theory and load conservation theory,the calculation method of the range and stress of each area was proposed.According to the deformation characteristics of surface subsidence,the flank of surface movement basin was determined to be the stope boundary-affected area,and the calculation method of strata length in each zone of stope boundary-affected area was proposed.According to the overburden damage degree,combined with the stress and deformation of overburden induced by mining,the permeability subarea characteristics in stope boundary-affected area were analyzed qualitatively.(2)The influence of the parameters of double-yield model embedded in FLAC3 D on materials mechanical behavior was analyzed,and the accurate matching method of numerical simulation parameters for the nonlinear compaction characteristics of the caving rock in the goaf was proposed.By monitoring stress and strain in numerical simulation process,the overburden state of caving and accumulation could be judged,and the strata parameters were modified simultaneously,so the numerical simulation of dynamic evolution process of overburden caving,accumulation and compaction could be realized.Based on this,the distribution characteristics of superimposed stress field from the two adjacent stope boundary-affected area were revealed,and the stress path in the process of spatial dynamic change of stopes on both sides was given.(3)A semi-infinite elastic foundation beam model of overburden continuous deformation above the goaf and coal pillar was established,which revealed the tensile and shear failure characteristics of interface in the process of strata group collaborative deformation.Based on the cooperative deformation of rock strata and limit equilibrium condition of shear stress,a calculation method of tension separated fracture and shear dislocated fracture was proposed.The mechanism of vertical fracture development induced by tensile stress and intensified by shear stress was revealed,and calculation methods of vertical tension fracture considering the tension stress balance at the crack tip and vertical shear fracture considering the shear stress balance on the effective bearing section of the fractured rock were proposed.(4)The deformation and failure characteristics and permeability evolution laws of rock under mining stress path were analyzed.Based on the correlation characteristics of deformation and acoustic emission signals in the process of rock damage evolution,a modified Lemaitre damage variable characterization method considering the axial strain damage threshold,residual deformation and secondary loading & unloading deformation was proposed,and the permeability evolution model of rock with combined damage of shear and tension failure was established.Based on this model,the dynamic evolution of permeability and seepage field in the process of meso damage to macro fracture and fracture closure is analyzed.(5)According to the evolution laws and distribution characteristics of the overburden permeability under the spatial dynamic change of adjacent stopes and the superposition of mining influence,the stope boundary-affected area was divided into permeability attenuation area,permeability superposition area,tensile permeability enhancement area,permeability stability area,permeability recovery area,permeability constant increase area and permeability sharp increase area.This paper analyzed the control laws of coal pillar parameters on the permeability of dangerous areas such as permeability superposition area and permeability constant increase area,and put forward the control methods of vertical seepage of overlying water body and lateral seepage of adjacent goaf hydrops.This dissertation contains 128 pieces of figures,18 pieces of tables and 204 pieces of references.