The catastrophic failure in coal mines, known as bumps, is one of the most challenging engineering problems associated with coal mining in highly stressed conditions. In this study, coal samples obtained from a Utah coal mine are investigated by conducting laboratory tests. However, the results of the unconfined compressive test do not agree with the strength models of the classical strength formula because the strengths at certain orientations of cleats appear much higher than the estimation by the classical solution. The influence of non-persistent cleats on coal strength is, thus, also investigated using a numerical modeling approach. The 3DEC models are developed to randomly generate cleats with various lengths that follow a given degree of persistence in the numerical model. The 3DEC simulation results successfully replicate the results of the laboratory test for the coal strength with non-persistent cleats. It is concluded from the study that cleat persistence significantly affects the overall anisotropic strength of coal.

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