Research on coal bedding effect based on indirect tensile test

By using several advanced macro and micro test methods,the bedding structure and mineral distribution of coal were analyzed,which lay the foundation for the study on the mechanism of coal rock bedding effect. Indirect ten- sile test and acoustic emission (AE) test in which loading direction is parallel and perpendicular to the bedding plane of coal were conducted,and the failure mechanism,bedding effect on tensile mechanical properties,as well as the bed- ding effect on AE timing parameters,law of energy release,spatial evolution characteristics and the damage variable D during the stretching process were analyzed. The results show that,the calcite mineral mainly distributes along the bed- ding plane and it plays an important role in the process of initiation and development of cracks. The tensile strength of coal whose loading direction is parallel and perpendicular to bedding plane is 0. 706 and 1. 039 MPa,respectively. Compared with the vertical group,the AE activity of parallel group is weaker in the whole process,and AE events in- crease sharply in a short time when approaching to failure,the failure occurs suddenly and the main fracture surfaces distribute along the bedding plane. The AE signal of vertical group appears at the beginning of the loading,the AE ring count rate and energy rate are higher than the parallel group and the spatial localization of vertical group has an obvi- ous nucleation area. The damage variable D in the vertical and parallel groups shows an obvious different characteristic with ladder type and two-section type,respectively. The rock damage state based on AE energy is more coincident with reality.