ACOUSTIC EMISSION CHARACTERISTICS AND FAILURE MECHANISM OF ROCK MASS WITH IN-SITU DIRECT SHEAR TEST

Acoustic Emission(AE)technology is mainly used in examing the failure characteristics of small-scale rocks(≤10 cm). However, there are few studies on the damage characteristics of large-scale rocks with regard to AE technology. Large-scale rocks(≥70 cm) are closer to engineering reality and can better reflect the true fracture state of engineering rock masses. In this study, we use in-situ direct shear experiment combined with AE technology and analyzes the AE signal of soft carbonaceous biotite schist using AE parameter analysis, AE waveform, and time-frequency analysis technology. The results of this study show the follows. First, the shear failure process of rock mass can be divided into the following three stages: (1)the crack initiation(elastic deformation) stage when there is no or very weak AE event in the rock mass, (2)the crack propagation stage when a small number of microcracks can be observed in the rock mass and continue to expand, and AE events accumulate, but the overall number is small, and (3)the destruction stage when AE events increase significantly, and microcracks continue to expand and penetrate until macroscopic fractures are formed. Second, we analyze the CV(r) value of the statistical indicator variation coefficient based on the r value and compared it with the b value based on amplitude statistics. We find that the results of CV(r) and b value have opposite feature. The conclusions of this study are the AE events appear firstly in the rock mass subjected to shear load, and the newly added AE events gradually move forward with the increase of shear load, which indicates that the micro-fractures first surround the force-bearing part of the direct shear test rock mass. In the stage of rock mass destruction, micro-cracks are concentrated in local areas, and the rock mass produces stress concentration. In the future, the combination of AE technology and direct shear test can be used to monitor and predict the dynamic shear failure behavior characteristics of engineering rock mass structural planes, predict rock failure precursors, and be used as a beneficial means for mutual verification of on-site direct shear test results.