Study On Three-Dimensional Shape And Co-Evolution Effect Of Mining Stress-Fracture Field In Inclined Coal Seam

Coal is the most important primary energy in China,which occupies a dominant position in daily production and life.However,due to the long-term consumption of coal resources,more and more mines have begun to gradually ask for resources in the deep in recent years,and coal seam mining is also facing a series of complex problems.Among them,the mining of inclined coal seam under water is an important problem that people pay more and more attention to.In the process of coal seam mining,the deformation space of the upper roof is relatively increased,which leads to more severe deformation and failure of the overlying rock.At the same time,it will also cause the generation,change and expansion of the overlying rock fissures.The stress is highly concentrated in the local area,which makes the roof control more difficult,which is more likely to lead to the occurrence of water inrush accidents,which seriously threatens the life and property safety of the staff.Therefore,it is particularly important to study the space-time effect and evolution law of overburden stress-fracture field in the process of inclined coal seam mining.Based on the 182706 working surface of sycamore,this paper analyzes the evolutionary characteristics of the stress-crevice field of the surrounding rock during mining by combining similar material simulation,discrete element and finite difference numerical simulation software.The space-time evolution model of stress-crack field is established,and its co-evolution law is analyzed,which provides a theoretical basis and technical support for the safe and efficient production of working surface and the safety of workers.The main work and research results are as follows :(1)Through the empirical formula,the theoretical height of the“upper three zones”of the overburden is calculated.The height of the overburden caving zone in the 182706 working face is 8.6 ～ 19.4 m,and the height of the fracture zone is 35.1 ～ 68.5 m.Through UDEC numerical simulation,it is concluded that the roof fracture development height is stable to the vicinity of the key layer,and the overall fracture development height is about 69.2 m.(2)Through the simulation of similar materials,it is concluded that the fracture development distance of deep rock strata has experienced two stages of “first increase and then decrease”.The stress evolution of coal seam floor has experienced three forms(“V” type,“W” type and “rotational symmetry” type).Through UDEC numerical simulation,it is concluded that the transfer path of overburden stress presents an asymmetric arch shape,and the stress is transmitted to the upper and lower coal bodies of the coal seam respectively.The stress of overburden rock at the lower end of the coal seam is mainly transmitted to the deep rock mass on the left side,and the stress of overburden rock at the upper end is mainly transmitted to the floor direction.The fracture zone is highly developed to the key stratum,and the fracture zone gradually evolves from the “irregular arch” form to the “transversely developed trapezoid” form.(3)The distribution of stress concentration shell is mainly concentrated in the surrounding rock around the goaf.The rock mass behind the open-off cut and the rock mass in front of the goaf show a symmetrical shape,and the development height of the shell top is basically the same.The stress relief ladder body gradually converges from the coal seam to the overlying strata and the underlying strata,and the convergence curvature of the overlying strata is much larger than that of the underlying strata.(4)The stress unloading zone(fracture zone)is mainly concentrated at the upper corner of the goaf,which is also the place where gas is easy to accumulate.Above the fracture field,it is always enveloped by the stress concentration shell composed of high stress.The synergistic effect of stress field and fracture field evolves the migration and failure of surrounding rock in stope.(5)In the spatial-temporal evolution model of stress-fracture field,the stress shell shows asymmetry as a whole.In the direction of strike,the stress of overlying strata shows a symmetrical “arch” shape.In the direction of coal seam tendency,the stress of overlying strata shows an asymmetric “arch” shape,and the center of stress arch is located in the upper area of goaf.