Study on the characteristics of AE b-value during granite failure process under biaxial loading

Based on the acoustic emission (AE) locating technology, the experiment study of fracture mechanism and time and space distribution characteristics of the change of b-value for granite rock acoustic emission under biaxial compression is conducted.The results show that k value, the ratio between axial stress corresponded by peak AE rate and axial compressive strength, shows a decreasing trend with the appearance of the lateral pressure.When lateral pressure is zero, k value is about 0.87.When the lateral stress is 5~25 MPa, k value is obviously lower than 0.8.The change rule of b-value in the biaxial experiment increases firstly, then decreases with the stress increasing.With the increasing of the lateral pressure, the peak of b-value appears in lower stress range.Without the lateral stress, b-value begins to decrease when the axial stress reaches 80% of the axial peak stress.When the lateral stress ranges from 5 to 25 MPa, the axial stress corresponding to the peak of b-value is apparent less than 80% of the axial peak stress.This is because the lateral pressure makes samples reach the peak AE rate earlier and enter the unstable stage of crack propagation earlier.The research results are of great significance to understand rock failure under biaxial loading.