Outburst of coal and gas is a major hazard in underground coal mining where coal seam gas content/pressure is high. A cone-shaped cavity is often observed in the coal seam after bursting, implying the likely mechanical structure being formed during outburst propagation. Although the mechanism for outburst initiation and propagation is very complex, mining-induced fracturing and damage of the coal material is an essential component. This paper investigates the mechanical conditions that are essential to initiate fractures around a spherical cavity, a simplified form of the cone-shaped outburst cavity. The cavity is assumed to be situated in an infinite isotropic homogeneous elastic body under internal gas pressure and far-field hydrostatic compressive stresses as a further simplification for analytical investigation. The analytical conditions under which circumferential and radial fractures can initiate around the cavity are formulated, based on extensional strain criterion for fracture initiation. Low internal pressure on the cavity surface and high far-field compression lead to circumferential fractures. In contrast, high internal pressure and low far-field compression lead to radial fractures. Subsequent numerical simulations with FRACOD^3D and FRACOD, the 3D and 2D in-house fracture simulation codes, were carried out to investigate fracture patterns around a cavity and inclusion. The simulation results confirmed the analytical results, including fracture shapes and the size of fractured zone. These results provide a new angle to understand the complex mechanism of outbursts.

中文翻译：

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研究球形空腔周围的断裂模式以了解爆发传播机制

煤与瓦斯突出是煤层瓦斯含量高、压力高的地下煤矿开采的主要危害。煤层爆破后经常观察到锥形空腔，这表明可能是突出传播过程中形成的机械结构。尽管突出发生和扩展的机制非常复杂，但采矿引起的煤体破裂和损坏是一个重要组成部分。本文研究了球形空腔周围引发断裂所必需的机械条件，球形空腔是锥形突出空腔的简化形式。假设空腔位于内部气压和远场静水压应力下的无限各向同性均匀弹性体中，作为分析研究的进一步简化。基于断裂引发的拉伸应变准则，制定了在空腔周围引发周向和径向断裂的分析条件。腔表面的低内压和高远场压缩导致周向断裂。相反，高内压和低远场压缩会导致径向骨折。随后使用 FRACOD ^3D和 FRACOD（3D 和 2D 内部断裂模拟代码）进行数值模拟，以研究空腔和夹杂物周围的断裂模式。模拟结果证实了分析结果，包括裂缝形状和裂缝区域的尺寸。这些结果为理解爆发的复杂机制提供了一个新的角度。