Development of a Synthetic Rock Mass Model and Its Application in Simulating the Strength Behavior of Fractured Coal Masses in 3D

The complex fracture network and stress state make the mechanical properties of coal mass very complicated, and the strength of the coal mass is difficult to determine via direct measurement. Therefore, the reasonable prediction of coal mass strength has become a key issue in coal mining engineering. To find a solution to this problem, computed tomography scanning technology was used to detect the preexisting fracture networks of cubic coal blocks. We improved the test method for intact coal mechanical parameters and created a more refined fracture network. Meanwhile, particle interlocking and nonlinear stiffness problems in synthetic rock mass are optimized. Based on the developed synthetic rock mass method, a series of true triaxial compression tests were conducted on coal masses under different fracture networks and confining conditions. The results show that bedding planes, cleats, face cleats, and butt cleats have different weakening effects on intact coal and that the influence of the confining pressure on the strength of coal has obvious nonlinear characteristics. By introducing the joint coefficient Jf and the intermediate principal stress σ2, the strength criterion of a complexly fractured coal rock mass in the form of a power index is established. The strength criterion can be used to predict the strength of a coal mass containing complex fractures through comparisons with laboratory triaxial test data.