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为研究超前裂纹对坚硬顶板内力变化的影响和顶板“反弹”、“压缩”特性,将煤壁前方煤层和直接顶视为弹性地基,假定在裂纹发生初始阶段顶板上方荷载不变,以最大拉应变强度条件为裂纹发生条件,对初次来压前的坚硬顶板进行分析,求得满足裂纹面边界条件、自然边界条件和连续条件的裂纹发生初始阶段顶板内力和挠度形式解中全部系数。据所得表达式,采用Matlab软件给出算例。算例表明:1裂纹面在煤壁前方,其位置在见报导的顶板超前断裂位置范围内。采空区的顶板下沉量随超前裂纹生长而明显地增大。在裂纹面附近区域顶板挠度发生反弹,在反弹区前方存在压缩区,与现场监测到的顶板“反弹”、“压缩”特性一致。2末排支护为顶板弯矩反弯点,随超前裂纹生长,末排支护前方顶板上侧受拉弯矩全面减小,而其后方顶板下侧受拉弯矩全面增大。煤壁前方顶板剪力随裂纹生长逐渐减小,煤壁后方顶板剪力不变。所得结果对于采场顶板状况的判断有一定的参考价值。
In order to study the effect of advance crack on the change of internal force of hard roof and the characteristics of roof “rebound” and “compression”, the coal seam in front of coal wall and direct roof are regarded as elastic foundation. Assuming that the load on the roof is unchanged in the initial stage of crack initiation , The condition of crack initiation under the condition of maximum tensile strength was used to analyze the hard roof before initial pressing. All the solutions of the internal force and deflection of the roof in the initial stage of crack initiation satisfying the boundary conditions of the crack surface, the natural boundary conditions and the continuous condition coefficient. According to the obtained expression, Matlab software is used to give examples. The example shows that: 1 The crack surface is in front of the coal wall and its position is within the reported range of the roof leading fault. The amount of roof subsidence in the goaf increases significantly with the advance of the crack growth. In the vicinity of the crack surface, the deflection of the roof rebounds, and there is a compression zone in front of the rebound zone, which is consistent with the monitored roof “rebound” and “compression” characteristics. 2 The end support is the bending moment of the roof bending point. With the advance of the crack growth, the bending moment at the upper side of the roof in the last row is reduced completely, while the bending moment at the lower side of the roof is increased. The shear force of the roof in front of the coal wall decreases gradually with the crack growth, and the shear force in the roof of the coal wall does not change. The results obtained for the judgment of stope roof condition has a certain reference value.