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Abstract Aiming at the support crushing accidents during the faces mining out of the upper 1-2 goaf-side coal pillar in panel of coal seam 1-2 of Shigetai coal mine，the mechanism and its prevention measures are researched based on the field measurement，simulation experiments and theoretical analysis. The results show that when the cut-hole of the lower seam was set under the upper coal pillar，the working face would go through the mining stage from the area under the coal pillar to that under the goaf，which was called the mining out of the upper goaf-side coal pillar. In the mining process，two situations exist in the support crushing by the influence of the cut-hole position. If the distance between the cut-hole and the upper coal pillar boundary is larger than the first breaking step of the key stratum(KS) above the pillar，the periodic breaking block of the KS and its broken block at the side of goaf near the pillar boundary will form an unstable three hinged structure when mining out of the pillar；and the excessive load caused by the relative rotary motion of the structure is the fundamental source for the support crushing. If the distance is between the first breaking and periodic breaking step of the KS，the KS will present the cantilevered breaking state when mining out of the pillar；and the support crushing is caused by the excessive load due to its long breaking span. Meanwhile，when the KS breaking span is more than 1.7–1.9 times the length of its periodic broken step，the risk level of the support crushing will be obviously higher than that in the former situation. The simulation experiments and engineering practices show that the support crushing accident during the mining out of the upper goaf-side coal pillar can be effectively controlled by reducing the distance between the cut-hole and coal pillar boundary，so as to prevent the breaking of the KS above the pillar.
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Received: 08 October 2012
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2013, Vol. 32 
