| Deep fully-mechanized top coal caving mining can easily induce movement and fracturing of thick and hard strata in the far and near fields,which cause large-scale and high-intensity mining disturbances and lead to frequent occurrences of coal burst.Exploring the influence of tremor sources energy levels and distances from coal seam,and determining the key thick and hard stratum that induce coal burst,are crucial in preventing the impact manifestations of gob-side roadway,which are induced by the fracture and synergistic movement of thick and hard rock strata.This paper comprehensively adopts a research methodology that combines laboratory experiments,theoretical analysis,numerical simulation,and field practice.It focuses on the progressive failure mechanism,stress and energy evolution of coal and rock combined specimens under high static load and impact disturbances.It investigates the evolution characteristics of mining-induced stress,displacement(deformation)of overlying strata,and acoustic emission(AE)events induced by the fracture of thick and hard strata,as well as the stress environment and impact manifestation mechanism of gob-side roadway.This research provides a foundation for the safe and efficient mining of deep ultra-thick coal seams.The research results are as follows:(1)The progressive failure mechanism,stress and energy evolution of coal and rock combined specimen under high static load and impact disturbances are revealed.Using a self-developed triaxial dynamic and static loading test system,experiments were designed to investigate the response characteristics of coal and rock combination specimens under both high static load and high static load combined with impact disturbance.A comparative analysis was conducted on the progressive failure characteristics of coal and rock combination specimens,as well as the response patterns of fractal dimensions of fractured coal and rock blocks and acoustic emission events.The strength characteristics and crack propagation patterns at the interface of coal and rock formations were obtained,and the stimulating effect of impact disturbances on the dynamic manifestation of coal and rock combination specimen was quantitatively evaluated.(2)Based on the response characteristics of multi-source geophysical information to mining activities,a method for identifying the main thick and hard stratum that induces dynamic manifestations of gob-side roadway when fractured was proposed.A large-scale three-dimensional physical simulation test and multi-source geophysical information acquisition system was constructed.Physical simulation experiments were conducted to investigate the three-dimensional evolution of multiple fields induced by mining activities,allowing for the observation of the fracture and synergistic movement of thick and hard roof strata,as well as the three-dimensional scale response characteristics of the stress field,displacement field,and vibration field.The key thick and hard stratum inducing instability of the coal and rock combination,affecting the stability of gob-side roadway surrounding rock,was determined.(3)Established the instability criteria for the overlying structure model of "thick-hard strata and coal-rock combination".Using the mechanical model of deformation and fracture of thick and hard roof strata on an elastic-plastic foundation,we analyzed the influence of overlying load,plasticity coefficient of the foundation,width of the hanging area,and degree of stress concentration on the deformation,energy accumulation and release,of thick and hard roof strata under mining activities.The main release area of elastic energy was identified for different unstable overlying structures during the mining process,including initial fracture and periodic fracture of thick-hard strata and voussoir beam.Based on the loading characteristics in coal and rock combination of gob-side roadway,the types of failure for the "thick-hard strata and coal-rock combination" structure were classified as "mining tremor with non-impact manifestation","non mining tremor but with impact manifestation" and "mining tremor-induced impact manifestation".Corresponding instability criteria were also provided.(4)The effect of the tremor source,induced by the fracture of thick-hard strata,including energy level and the distance from tremor source to coal seam,resulting to the impact manifestation of gob-side roadway,is clarified.we constructed a numerical model for the mining of ultra-thick coal seams with multiple thick-hard rock strata,and analyzed the response characteristics of the overlying stress field,fracture field,and energy field to mining activities.We discussed the influences of factors such as the strength and thickness of thick and hard roof strata,as well as the distance from thick and hard roof strata to coal seam,on the distribution of multiple fields.We obtained the evolutionary laws of gob-side roadway surrounding rock velocity field and acceleration field when the thick and hard roof strata fracture.Additionally,we clarified the disturbance to the coal and rock combination of gob-side roadway caused by the deformation and fracture of thick and hard roof strata.(5)Summarized the prevention strategies for dynamic manifestations of gob-side roadway induced by the fracture of thick and hard strata.Utilizing prevention technologies such as pre-split blasting of roof and floor,large-diameter destressing boreholes,and coal seam water injection,a comprehensive technological method aimed at altering the physical and mechanical properties of coal and rock combination bearing structure was constructed.This method serves to weaken dynamic loading intensity and transfer high-static loads away from roadway.Engineering practices and effectiveness evaluations were conducted to address the prevention of dynamic manifestations in coal and rock combinations of gob-side roadway.Figure [113] Table [24] Reference [224]... |
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