Characterizing a coal from an engineering perspective for design of mining excavations is critical in order to prevent fatalities, as underground coal mines are often developed in highly stressed ground conditions. Coal pillar bursts involve the sudden expulsion of coal and rock into the mine opening. These events occur when relatively high stresses in a coal pillar, left for support in underground workings, exceed the pillar's load capacity causing the pillar to rupture without warning. This process may be influenced by cleating, which is a type of joint system that can be found in coal rock masses. As such, it is important to consider the anisotropy of coal mechanical behavior. Additionally, if coal is expected to fail in a brittle manner, then behavior changes, such as the transition from extensional to shear failure, have to be considered and reflected in the adopted failure criteria. It must be anticipated that a different failure mechanism occurs as the confinement level increases and conditions for tensile failure are prevented or strongly diminished. The anisotropy and confinement dependency of coal behavior previously mentioned merit extensive investigation. In this study, a total of 84 samples obtained from a Utah coal mine were investigated by conducting both unconfined and triaxial compressive tests. The results showed that the confining pressure dictated not only the peak compressive strength but also the brittleness as a function of the major to the minor principal stress ratio. Additionally, an s-shaped brittle failure criterion was fitted to the results, showing the development of confinement-dependent strength. Moreover, these mechanical characteristics were found to be strongly anisotropic, which was associated with the orientation of the cleats relative to the loading direction.

中文翻译：

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考虑割理各向异性的犹他州煤的约束依赖特性试验研究

从工程角度表征煤炭对于采矿开挖设计至关重要，因为地下煤矿通常是在高度压力的地面条件下开发的，以防止死亡。煤柱爆裂涉及将煤和岩石突然排入矿井开口。这些事件发生在煤柱中相对较高的应力，用于支撑地下工程，超过了煤柱的承载能力，导致煤柱在没有警告的情况下破裂。这个过程可能受到割理的影响，割理是一种可以在煤岩体中发现的节理系统。因此，重要的是要考虑煤力学行为的各向异性。此外，如果煤预计会以脆性方式失效，则行为会发生变化，例如从拉伸破坏到剪切破坏的转变，必须考虑并反映在采用的失效标准中。必须预见到，随着约束水平的增加和拉伸破坏的条件被阻止或大大减少，会发生不同的破坏机制。前面提到的煤行为的各向异性和约束依赖性值得广泛研究。在这项研究中，通过进行无侧限和三轴压缩试验，对从犹他州煤矿获得的总共 84 个样品进行了调查。结果表明，围压不仅决定了峰值抗压强度，而且决定了脆性作为主要与次要主应力比的函数。此外，S 形脆性破坏准则适用于结果，显示了约束依赖强度的发展。而且，