An experimental study of Lode angle impact on the rock failure procession based on acoustic emission

The laws of acoustic emission (AE) before and during rock failure are different under different stress states. In this article, a new multi-functional true triaxial geophysical (TTG) apparatus was applied to analyze the AE law of sandstone under different stress paths. The results show that (1) with the increase of Lode angle, the tensile fractures in the sandstone increase initially, followed by a decrease. The number of AE decreases initially, followed by an increase, while the average energy of AE signal increases initially, followed by a decrease. (2) During the loading process, the IB values of rock can be divided into wave type, band type and mixed type, which represent crack propagation process driven by external force, self-driving and mixed driving. It can provide a basis for early warning of underground engineering construction disasters. (3) The variation characteristics of RA and AF in rock failure process show the corresponding relationship with IB value. The RA value corresponding to the IB value of band, wave and distribution type distribution mainly concentrated around 0.05, 0.03 and widely distributed, respectively. According to the value of RA, the types of cracks show different characteristics under different driving forces. (4) With the increase of Lode angle, the failure types of rocks change from single oblique fracture (- 30 degrees) to double-X-type fracture (10 degrees), and finally changes to single-X-type fracture when Lode angle is 30 degrees. The fracture angle of rock decreases initially, followed by an increase with the increase of Lode angle. Therefore, it is important to explore the AE law of rock failure process under different stress states for the early warning of underground engineering construction disasters, and can provide a guidance for the application of human underground space. With increasing Lode angle, the number of acoustic emission (AE) signals in rock first decreases then increases, while the average AE energy first increases then decreases.The improved b-value (IB) of AE can indicate the crack propagation mode as driven by external force, self-driving, or mixed-driving, providing a basis for early warning of underground construction disasters.The fracture angle and failure mode of rocks change with increasing Lode angle, from single oblique to double X-type, and finally to single X-type fractures.