Research On Asymmetrical Deformation Mechanism And Control Countermeasure Of Dynamic Pressure Roadway Under Close Range Gob

The mining activity of the coal below the gob not only bears the concentrated stress of the remnant coal pillars above,but also is imposed by dynamic events such as blasting,drilling,coal cutting and gas outburst,etc.It was easy to lead to the secondary fracture and collapse of the roof above the gob,fault sliding and other dynamic loading disturbances.The dynamic stress wave spreads to the roadway below the gob,which may induce dynamic disasters such as rock burst.Against above research background,use comprehensively indoor mechanics experiment,numerical simulation and theoretical analysis,rock mechanics,mechanics of materials,structural mechanics,mining pressure and strata control,elastic mechanics and rock dynamics,etc.this paper studies response of coal and rock around roadway under the gob subjected to dynamic pressure.The mechanical model and asymmetric deformation mechanism of surrounding rock of dynamic pressure roadway under gob are then analyzed,the asymmetric deformation mechanism of mining roadway under gob under dynamic load disturbance are then revealed.The supporting technology and prevention and control measures of surrounding rock of roadway under gob is pertinently put forward.The main research achievement of this paper are as follows:(1)The typical characteristics and influencing factors of dynamic pressure roadway under gob are revealed.Through the analysis of the stress redistribution process of surrounding rock after overlying coal seam mining,it is concluded that the stress distribution of the roadway under the gob is uneven,the ground stress is the foundation of the static stress,and the stress concentration is high.By analyzing the main dynamic load sources of roadways under gob and the wave forms of various dynamic stress waves monitored on site,it is concluded that the dynamic loading of roadways under gob has the characteristics of short action time,attenuation,volatility,direction randomness,multiple disturbance and uneven distribution.By analyzing the specific situation of roadway under the gob,it is concluded that the asymmetric deformation of roadway surrounding rock under gob is reflected in large deformation of key positions,the stress asymmetry after coal seam extraction,the overall deformation asymmetry of roadway and the failure asymmetry of symmetrical support components.(2)The instability response characteristics of coal and rock mass around dynamic pressure roadway under gob are obtained.The bearing response characteristics,deformation and failure characteristics,surface displacement field and strain field evolution characteristics of coal samples,AE energy,AE ringing number and AE fracture point distribution characteristics of coal under single load loading and different dynamic and static combined loading under different strain rates were explored.The influence degree and influence law of coal sample instability and failure under different static load stress and dynamic load parameters were analyzed.When the dynamic load suddenly acts on the coal sample,the coal sample shows obvious Kaiser effect,and the AE fracture location of the coal sample is basically consistent with the real failure mode of the specimen.Static loading is the basic stress condition for the induced impulse of the dynamic-static combination of coal,and dynamic load is the inducement for the failure of the dynamic-static combination of coal.(3)The stress distribution characteristics and asymmetric deformation mechanism of surrounding rock of dynamic pressure roadway under the gob are revealed.According to the caving gob roof with stope activity law,the dynamic load stress response expressions under the action of uniform dynamic load and concentrated dynamic load on gob floor are obtained.Based on the elastic half-plane infinite body theory,the limit equilibrium theory and the dynamic foundation half-space theory,a theoretical model of the abutment pressure of the gob and the remnant coal pillars and the theoretical calculation model of the dynamic load caused by the roof collapse of the gob are established,and the expression of the time-history relationship between the vertical stress,horizontal stress,shear stress and the impact stress of the floor strata in the gob at any point in the floor coal and rock mass under the gob is derived.The self-stabilized hidden arch theory is further used to solve and predict the maximum unstable region of roadway surrounding rock under gob,and the asymmetric deformation mechanism of roadway under close gob is deeply analyzed.The asymmetric deformation mechanism of roadway is further analyzed by FLAC^3D numerical software.The displacement and deformation characteristics of the numerical calculation of roadway are consistent with the shape of the limit self-stable invisible arch curve obtained by theoretical calculation.(4)The characteristics of response to the dynamic loading and deformation evolution of roadway under the gob are studied.According to the engineering background of dynamic disturbance of roadway under the gob,the numerical model of dynamic and static loading superposition of roadway under the gob is established.The nonlinear dynamic module in FLAC^3D software is used to analyze the evolution of dynamic deformation of roadway surrounding rock.The dynamic loading response characteristics of displacement acceleration field,plastic zone,displacement field and strain field of roadway surrounding rock under dynamic and static loading superposition were studied under different buried depths,different dynamic stress wave amplitudes and different dynamic stress wave frequencies.The influence degree and influence of different conditions on the response characteristics of roadway were analyzed,and the asymmetric deformation mechanism of roadway under dynamic loading disturbance was revealed.(5)Control and prevention measures of surrounding rock deformation of dynamic pressure roadway under the gob.According to the mechanical analysis of bolt-mesh-cable support components,the reasonable asymmetric support parameters for roadway under close gob are further determined by using self-stabilized hidden arch theory,and the optimized support scheme is verified by numerical simulation.Starting from the dynamic load source of roadway under the gob,the stress concentration of remnant coal pillar and the characteristics of surrounding rock fragmentation,the dynamic pressure roadway prevention measures of“backfilling to eliminate dynamic load source”,“coal pillar blasting to reduce static load concentration”and“composite anchor grouting to strengthen surrounding rock bearing”are proposed.