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Received Aug 31, 2017; Revised Nov 27, 2017; Accepted Dec 4, 2017
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1. Introduction
The characteristics of rock strength and deformation will be affected by high temperature [1–9]. Many rock engineerings, such as nuclear waste disposal [10], geothermal resource development [11, 12], underground engineering stability [13], postdisaster reconstruction [14, 15], and other projects, are inevitably related to high temperature. The related mechanical parameters are the basis for the study of excavation and stability in underground engineerings.
The peak strength is the macroscopic representation of rock, which cannot reflect internal damage evolution. As an important method in acoustic nondestructive testing, rock internal defects and damage evolution process can be accurately monitored by acoustic emission (AE) detection [16–19].
In recent years, AE detection technology has been used in rock mechanics by many scholars [20–27]. For example, Ganne et al. [20] studied the brittleness of rock before peak stress by the AE technique, and four stages of accumulated AE energy were given. Alkan et al. [21] determined the expansion boundaries of rock by studying AE signals of different strain stages in triaxial compression tests. He et al. [22] observed that there were much higher amplitude and lower frequency events near the bursting failure of rock samples, and the accumulated AE energy release increased rapidly from unloading state to rock failure. Gasc et al. [23] studied rock structural transformation and mineral reaction under high temperatures and high pressures by X-ray diffraction and AE detection of serpentine. Chmel et al. [24] studied AE energy release of granite under impact loading. Zhang et al. [25] studied AE properties of halite, glauberite, and gypsum during compression test with different loading styles and saturation conditions. Zhang et al. [26] calculated the correlation fractal dimensions of AE counts at different stress levels, and the value at the failure point showed a polynomial decline with the increase of temperature. Guo et al. [27] carried out comprehensive studies on rock-detected AE characteristics, failure mode, crack initiation stress, damage evolution law, and stress-strain constitutive model after thermal damage.
Since AE monitoring technology has practical application in the...