近直立特厚煤层直接顶初次破坏特征

摘要

近直立煤层在开采过程中直接顶的破坏将直接影响采场及巷道的稳定,针对近直立特厚煤层采用水平分段开采过程中直接顶所处的应力状态及其破坏特点,建立了与之对应的四边固支的薄板力学模型;采用FLAC3D数值模拟和正交分析的方法开展4个因素3个水平9组数值模拟实验,模拟分析了埋深、倾角、侧压系数和最大主应力方向等4个因素对直接顶法向应力分布的影响特征,结果表明,近直立特厚煤层在开采过程中,作用在直接顶上的法向应力可以简化为均布载荷;采用伽辽金法求解了均布载荷作用下的直接顶挠度,并应用胡克定律和弧长定理对直接顶岩层不同位置处的拉应力进行求解,通过计算获得了直接顶在破坏前拉应力的最大值及其对应的位置;以最大拉应力强度准则为岩层破断依据,最终得到了近直立特厚煤层在采用水平分段综放开采条件下的初次破断垮距.%The immediate roof fractures of suberect and extremely thick coal in Sub-Level Top-Coal Caving directly affects the stability of the workface and roadway.According to the stress condition and the fracture characteristics of immediate roof in Sub-Level Top-Coal Caving,a four-edges-clamped plate model was introduced to calculate the deflection of immediate roof before the first fracture.To verify the normal stress distribution of the four thin plate models,FLAC3D software was used to perform the following tasks:simulating the mining process in the suberect and extremely thick coal seam mining face;undertaking an orthogonal numerical simulation experiment in three levels with different depths,coal seam angles,lateral pressure coefficients and orientations of maximum horizontal principal stress;translating the immediate roof stress of the corresponding nine simulation experiments into the suberect immediate roof normal stress;and using the above results to determine the distribution regularity of normal stress along the dip direction of the roof under the circumstance of different advancing distances and different subsections.According to the simulation resuits,the normal stress distribution of the immediate roof is uniform.The Galerkin method was used to calculate the solution of deflection equation under the effect of normal stress.The Hooke's law and the arc length theorem were used to calculate tensile stress of immediate roof,and obtained the maximum tensile stress and corresponding position of immediate roof before first fracture.Taking the maximum tensile stress strength criterion as the suberect immediate roof fracture criterion,the first fracture span could be obtained.