厚硬顶板弱化前后垮落致灾数值模拟研究

针对采空区大面积顶板垮落对采区机械设备及工作人员造成的冲击灾害问题，采用ANSYS/LS-DYNA有限元软件，建立顶板弱化前后块体冲击地面的三维计算模型，研究顶板弱化前后垮落体引起巷道内飓风风速的变化规律及冲击载荷对工作面煤层的影响。结果表明：在顶板下落过程中，由采空区到巷道口处，飓风速度呈增大趋势，且在巷道口处风速急剧增大，但风速在巷道内随着距巷道口距离的增大而衰减；随着顶板下落时间的增加，巷道内的风速整体呈上升趋势，但巷道内风速的衰减速率逐渐降低，且风速峰值随着所在位置与巷道口距离的增大呈对数衰减；大面积顶板垮落使工作面煤层出现应力集中现象，顶板弱化放顶循环步距控制在30 m以下可显著降低飓风的影响范围及冲击载荷对工作面煤层的影响。

Numerical Simulation of Collapse Disaster Before and After Weakening of Thick and Hard Roof

In view of the impact disaster caused by large area roof caving on mechanical equipment and workers in mining area，the related research was conducted relying on 210108 working face of Xinji No.2 Mine.According to the difference of block volume before and after roof weakening.A a three-dimensional calculation model of two kinds of caving bodies with the same height and width，coal seam，goaf and floor is established by using ANSYS/LS-DYNA finite element software.The calculation adopts Euler-Lagrange fluid-solid coupling algorithm.Rock and coal are described by Lagrange mesh and Lagrange element，air is described by ALE mesh and Euler element.The cloud map of hurricane velocity in goaf and roadway ，and the cloud map of effective stress in the bottom of coal seam in typical moment behind roof collapse are obtained by simulation under two kinds of calculation conditions.The variation rule of hurricane wind speed in roadway caused by collapse of different volume before and after roof weakening and the influence of impact load on coal seam in working face are analyzed.The results show that: For two kinds of condition，the attenuation law of hurricane velocity in goaf and roadway is basically the same，but the distribution characteristics of effective stress at the bottom of coal seam are different.From goaf to roadway entrance，hurricane speed tends to increase，and the wind speed increases sharply at roadway entrance，but the wind speed decreases with the increase of the distance between the location and the roadway entrance.With the increase of roof falling time，the wind speed in the roadway rises as a whole，but the attenuation and deceleration decay rate of the wind speed in the roadway decreases gradually，and the peak wind speed decreases logarithmically with the increase of the distance between the location and the roadway entrance.After roof weakening，the length of collapse body decreases，and hurricane wind speed decreases at different times.The maximum wind speed value ofin roadway entrance decreases from 298.62 m/s to 224.89 m/s，which decreases by 25\mathrm{\%}，and the reduction increases gradually with the increase of the distance to roadway entrance，which is 42\mathrm{\%} at 90 m.According to the fitting formula of the relationship between peak wind speed and distance，when the maximum allowable wind speed is 6 m/s，the influence range of Hhurricane after roof weakening decreases from 247 m to 158 m，which reduces by 36\mathrm{\%}.Large area of roof collapse causes stress concentration in coal seam of working face.After roof weakening，the stress distribution in coal seam of working face is more uniform，and the peak value of maximum effective stress decreases from 10 MPa before weakening to 4.3 MPa，which decreases by 57\mathrm{\%}.Controlling the cyclic step distance of roof weakening caving below 30 m can significantly reduce the impact range of hurricane and the impact load on the stability of coal seam in working face.