Experimental study on biaxial mechanical properties and acoustic characteristics of different damage granites after high temperature-water cooling

The high temperature-water cooling effect causes different degrees of damage to rock in underground engineering. The mechanical properties of the damage rock are related to the safety and stability of the engineering，and its acoustic characteristics are related to the failure analysis，prediction and early warning of surrounding rock. Relevant research has important scientific value and engineering significance. In this study，the biaxial compression test of granite with different damage degrees after high temperature-water cooling treatment was carried out by using true triaxial test system. Acoustic emission(AE) and microseismic(MS) systems were used to monitor the failure process of rock. The biaxial strength and deformation，acoustic signal evolution characteristics and precursor information of granites with different degrees of damage were analyzed. The influence of initial damage of rock on its fracture type was discussed，and the time-frequency domain characteristics of microseismic and acoustic emission signals were compared. The main conclusions are as follows. (1) The higher the initial damage degree(D) of granite，the lower the biaxial strength and elastic modulus of rock are. When D＞0.4，the decrease of biaxial strength and elastic modulus is significantly larger than that when D＜0.4. At the same time，the failure of rock samples changes from brittle mode to ductile mode，and the rock internal fracture changes from tensile type to shear type. (2) With the increase of rock damage degree，the AE cumulative absolute energy of rock samples decreases greatly. The evolution characteristics of acoustic signal parameters show obvious differences when D＞ 0.4 and D＜ 0.4. Compared with the rock samples with low damage degree，the moment of first sudden increase of AE hits and MS amplitude evolution curves of the rock samples with high damage degree generally appears earlier，more high amplitude signals emerge，and the duration of signal active period sustains longer. (3) Based on AE and MS signals，some precursor information of rock failure and the criterion of rock initial damage degree can be concluded. For example，the phenomenon that the MS fractal dimension increases and decreases sharply after the peak load can be used as a failure precursory information of the rock with different damage degrees，and the sudden decrease of MS or AE b value below 1 can be used as a failure precursory information of the rock with a low damage degree. The phenomenon that the AE b value decreases to less than 1 in the plastic stage occurs many times，and the MS fractal dimension fluctuates sharply before the peak load，which can be used as the basis for judging the initial damage degree of rock. The research results can provide reference for the analysis of surrounding rock stability and the evaluation of rock damage degree in underground engineering. © 2024 Academia Sinica. All rights reserved.