Abstract A strong and hard hanging roof causes high underground stress in underground mines, leading to rock burst, coal and gas outburst, or large deformations in roadways. To address these problems, hydraulic fracturing can form hydraulic cracks in strong hanging roofs and promote fractures in the hanging-roof. However, it is difficult to ensure that hydraulic cracks propagate vertically through rock strata. Therefore, a novel method has been proposed that uses hydraulic fracturing to generate vertical fractures in hard hanging roofs for-roof cutting and stress relief. The method exploits the additional horizontal tensile stress produced by the bending deformation of the roof so that the fracturing point occurs in a desirable tensile-stress area, and therefore to promote the vertical expansion of hydraulic cracks that cut off the rock strata. In this paper, the position of the maximum additional horizontal tensile stress is taken to be the reasonable fracturing position given by a mechanical model. Solving this model indicates that a shorter hanging roof equates to a thicker hanging roof, a larger elastic modulus, a smaller elastic cushion coefficient, and a fracturing position that is deeper in the coal wall. The various factors that affect the reasonable fracturing position may be ordered in terms of their impact as follows: hanging-roof length > hanging-roof elastic modulus > hanging-roof thickness > elastic cushion coefficient > horizontal stress. The proposed method has been applied to roadway 5103 of the Majiliang Coal Mine of Datong Coal Mine Group Co., Ltd. The results show that hydraulic fracturing forms vertical hydraulic cracks at the point of maximum additional horizontal tensile stress, which can effectively control the deformation in the surrounding rock. The fracturing position calculated by using this model is reasonable and reliable and can be used to guide the on-site construction.

中文翻译：

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水力压裂在硬顶顶上起裂垂直裂缝的位置以消除应力

摘要 强而硬的悬顶使地下矿井产生较高的地下应力，导致岩爆、煤、瓦斯突出或巷道大变形。针对这些问题，水力压裂可以在强悬顶形成水力裂缝，促进悬顶破裂。然而，很难保证水力裂缝垂直传播穿过岩层。因此，提出了一种新的方法，利用水力压裂在坚硬的悬顶上产生垂直裂缝，用于屋顶切割和应力消除。该方法利用顶板弯曲变形产生的附加水平拉应力，使断裂点出现在理想的拉应力区域，从而促进切断岩层的水力裂缝垂直扩展。本文将最大附加水平拉应力的位置作为力学模型给出的合理压裂位置。求解该模型表明，较短的悬顶等同于较厚的悬顶、较大的弹性模量、较小的弹性垫层系数以及较深的煤壁破裂位置。影响合理压裂位置的各种因素可按其影响排序为：吊顶长度>吊顶弹性模量>吊顶厚度>弹性垫层系数>水平应力。该方法已应用于大同煤矿集团有限公司马吉梁煤矿5103巷道。结果表明，水力压裂在最大附加水平拉应力点形成垂直水力裂缝，可有效控制围岩变形。使用该模型计算出的压裂位置合理可靠，可用于指导现场施工。