Time-space effect of overburden stress path in steeply dipping and large mining height stope

In order to reveal the spatial and temporal evolution characteristics and stress path effect of overlying strata deformation and failure in steeply dipping and large mining height stope, taking the 25221 working face of 2130 coal mine as the research background, the 3DEC numerical simulation method is used to determine and analyze the spatial and temporal evolution characteristics of overlying strata deformation and failure. The disturbance partition of overlying strata under the action of mining stress in steeply dipping stope is proposed, the spatial evolution law of mining stress path of overlying strata along the strike, inclination and different layers of working face is quantified, and the corresponding relationship between mining stress and fracture instability in different areas of stope space is revealed. The results show that in the mining of steeply dipping and large mining height, the gangue presents non-uniform filling characteristics under the action of gravity-dip angle effect, which leads to the typical cross-layer migration and transformation characteristics of overburden caving form and roof bearing arch in the stope space, and the hollow phenomenon is formed in the middle and upper part of the envelope surface "inverted triangle free surface + inclined masonry structure + high ladder rock layer". The structural instability of the "high ladder rock layer" is easy to induce the simultaneous fracture of the "inclined masonry structure" and form a large impact dynamic load on the support. Coal mining of working face results in significant changes in the magnitude and direction of three-dimensional mining stress of overlying strata. Along the strike of the working face, the maximum principal stress evolution of the overlying strata increases first and then decreases, while the minimum principal stress decreases first and then increases in the opposite direction. The maximum and minimum principal stresses rotate inward to the goaf along the vertical plane of the advancing direction, and the limit equilibrium state interface of the overlying strata is asymmetrically distributed along the inclined direction of the working face. Along the tendency of working face, the stress concentration occurs in the rock stratum above the coal pillar side, and the rock stratum above the working face is unloaded. The lower the overburden position, the greater the peak stress and the greater the stress variation. The maximum principal stress is mainly deflected along the horizontal direction, and the minimum principal stress is gradually deflected from the working face advancing direction to the vertical direction. From the weak disturbance area to the center of goaf, the reverse deflection position of stress gradually moves from the middle to the upper part, and the asymmetric deflection transfer characteristics of stress path become more and more obvious. The temporal and spatial evolution law of mining stress and the mapping relationship of mining stress-displacement-overburden fracture structure in steeply dipping and large mining height stope provide the basis for revealing the mechanism of surrounding rock instability. Combined with the actual production, the prevention and control measures of hard roof collapse and support crushing in a fully mechanized mining face with steeply dipping and large mining height are put forward.