Numerical simulation on the crack initiation and propagation of coal with combined defects

There is normally the occurrence of pre-existing cracks and holes in coal mass to influence its mechanical behaviours. And the crack initiation and propagation around the tip of pre-existing cracks can be observed to induce the overall failure of coal mass finally. In this study, two groups of hole with the radius of 10 mm connecting one crack with length and width of 20 mm and 1 mm, respectively, were pre-existed in sample to explore the influence of crack angle (from 0 to 90o) on the unconfined compressive strength (UCS), crack initiation and propagation, and failure modes of coal mass with combined faults by using RFPA2D. The results showed that the stress-strain curves of specimen with double-hole-crack exhibit multiple stress drop compared to that of intact coal sample, especially in the post-peak stage. Moreover, UCS decreased firstly with the crack angle increasing to 30o and then increased until the crack angle reaching to 75o following by decreasing with the continuous increase of crack angle to 90o. In addition, the failure mode of double-hole-crack specimen with the crack angle of 0-30o can be regards as the dominated tensile failure combined with shear failure, which was consist with the failure pattern of intact specimen. On the other hand, the failure mode of double-hole-crack specimen with the crack angle of 45-90o is the dominated shear failure combined with tensile failure. Meanwhile, the distribution characteristics of acoustic emission energy can be used to better reflect the deformation and failure process of coal mass with combined defects.