Development of new three-dimensional coal mass strength criterion

In this study, laboratory tests were conducted to obtain the geomechanical properties for the coal matrix and coal discontinuities. Computed tomography (CT) scanning technology was then used to detect the pre-existing fracture networks of the cubic coal blocks. Fracture tensor-based methodology was used to quantify the fracture geometry network that exists inside the cubic coal blocks. The same cubic coal blocks were subjected to the true triaxial tests to obtain the jointed coal mass strength (JCMS) values under different confining stresses. The fracture network constructed from the CT scanning was incorporated into the numerical model of jointed coal block to simulate the laboratory true triaxial tests, and to first calibrate the parameter values of the numerical model and then validate them. More numerical true triaxial tests were performed on some jointed coal blocks with selected fracture networks and five additional artificial fracture networks under different confining stress combinations to consummate the JCMS data bank. The obtained data bank was finally used to develop a new three dimensional (3D) coal mass strength criterion that can capture the scale effect and anisotropic strength behaviors.