Rock fracture mode and acoustic emission characteristics under true triaxial single-sided unloading path

Longpei MA Chongyan Liu ^* Guangming Zhao

• Anhui University of Science and Technology, Huainan, China

To investigate the fracture patterns of rocks and the characteristics of acoustic emission (AE) during the excavation and unloading process in underground engineering, the true triaxial disturbance unloading rock testing system along with the acoustic emission system were employed to carry out true triaxial single-sided unloading tests on coal, siltstone, fine sandstone, and granite. Integrating the Gaussian mixture model (GMM) clustering algorithm, a clustering analysis was performed on the characteristic parameters of acoustic emission to explore the damage and fracture patterns of the unloading rocks. The findings indicate that as the peak strength of the rock decreases, the fractal dimension of the ultimately broken fragments becomes larger, and the cracks within the failure zone develop more comprehensively. The higher the peak strength of the rock after single-sided unloading is, the greater its axial average elastic modulus will be. The acoustic emission ringing count and the b-value curve indicate that compared with siltstone and fine sand-stone, granite and coal are more prone to rock burst after unloading. In the RA-AF signals of coal and granite based on the GMM, the proportion of shear signals is as high as 66.05% and 69.21% respectively, which makes it easy to form shear cracks. While the proportions of tensile cracks in siltstone and fine sandstone are 41.43% and 56.41% respectively. Under the action of axial stress, they are prone to longitudinal splitting and form tensile cracks approximately parallel to the direction of the maximum principal stress.