Estimation of the rock mass strength has been a difficult task in the rock engineering practice. This research was focused on developing a new empirical model to estimate the 3-D coal mass strength, which can capture both the scale effect and anisotropic behavior. Both a laboratory experimental scheme and a numerical modeling scheme were carried out at the 3-D level. The laboratory experiments were performed to achieve the following:(a) Firstly, the geomechanical properties for the intact coal and coal discontinuities were estimated through the laboratory geomechanical property tests; (b) Secondly, naturally existing fracture networks in the cubic coal blocks were first detected by the industrial Computed Tomography (CT) scanning technique and then quantified by the fracture tensor based methodology; (c) Thirdly, polyaxial tests were conducted on the same cubic coal blocks to obtain the JCMS values under different confining stresses. With respect to the numerical modeling, the geometric models of the jointed coal blocks were set up to simulate the laboratory polyaxial compression tests under different confining stress combinations and to obtain a JCMS data bank. Finally, a new empirical model was developed to estimate the JCMS values at the 3-D level.

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