A procedure to detect, construct, quantify, numerically simulate and validate fracture networks in coal blocks

Coal mass is a typical sedimentary rock mass with three approximately orthogonal discontinuity sets: bedding planes, face cleats and butt cleats. The mechanical anisotropy of coal masses is dependent on this fabric to a large extent. In this paper, a framework incorporating X-ray computed tomography (CT) scanning, statistical analysis, the fracture tensor based methodology and a numerical stress analysis technique is proposed to detect, construct, quantify and simulate the fracture networks in coal blocks. The CT scanning was first used to obtain the geometric information of the fractures in cubic coal blocks. Then a statistical numerical procedure was proposed to estimate and construct the locations, orientations and sizes of the fractures. An overall assessment of the constructed fracture networks was next made using the fracture tensor based methodology to incorporate all the important features: number of joint sets, joint density, joint orientation and joint size. The fracture networks in cubic blocks were then numerically simulated through a proposed modified fictitious joint procedure to accommodate a large quantity of non-persistent joints with an acceptable numerical stress analysis effort. The framework was validated at different stages to evaluate the reliability. Finally, the implementation of this framework is shown by a numerical investigation of the influence of the fracture networks and confining stresses on the jointed coal mass strength. The proposed framework provides a systematic and innovative method to tackle the fracture network induced mechanical anisotropy of the fractured rock masses.