Mechanical and failure characteristics of flawed granite after high-temperature cycling: An experimental study using biaxial compression

Abstract

Unveiling the mechanical and failure characteristics of flawed granite subjected to high-temperature (HT) cycles is essential for assessing the stability of underground engineering. There is limited advanced knowledge of the rock performance under HT cycles even today. To that end, biaxial compression experiments with the simultaneous acoustic emission (AE)-digital image correlation (DIC) monitoring are conducted on flawed granite containing the flaw pairs, with the emphasis on the influences of HT cycles on the mechanical and failure characteristics of flawed granite. Experimental results suggest that the rock strength is increased at 400 °C, regardless of the cycle number, while it is weakened at 600 °C, especially under the thermal cycles. By the coupling analysis of acoustic-optical-mechanical data, the levels of cracking in flawed granite are revealed as the process zone nucleation and quasi-static growth, along with the macrocrack initiation, propagation, and coalescence until the eventual failure, dictated by the stress shielding effect and stress amplification effect. The splitting crack, hook crack, and far-field network crack are reported for the first time. Moreover, the flawed granite at different temperatures transitions from tensile-dominated cracks to mixed tensile-shear (T-S) cracks. Besides, thermal cycling causes rock fatigue damage, and the alternating thermal stress generated by HT cycling promotes the initiation and propagation of microcracks, leading to the development and further intensification of thermally induced fracture.