Effect of thermal shock on the strength and fracture behavior of pre-flawed granite specimens under uniaxial compression

An understanding of high temperature effect on the strength and fracture behavior of rock is a key concern in underground engineering. To study the strength evolution and cracking process of thermally-damaged rock, granite specimens containing pre-existing flaws were heated to different high temperatures and subjected to uniaxial compression. In this study, the pre-heated granite specimens were cooled to room temperature slowly in oven or rapidly in water. The mechanical test showed that the peak strength and elastic modulus of granite decreased slightly below 300 °C and then decreased significantly with the temperature. During the loading, a photographic, acoustic emission (AE) monitoring and a digital image correlation method were used to capture the crack evolution, AE and strain field of granite specimens. The experimental results demonstrated that strain concentration bands were first emanated from the tips of pre-existing flaws and developed with continuous increase of external stress, followed by the propagation and coalescence of macro crack. An optical microstructure observation test was carried out to explore the mechanisms of high temperature and cooling rate in altering mechanical properties of granite. At last, the influence of pre-existing flaw on the mechanical behavior of granite was illustrated by numerical simulation. The experimental and numerical results are expected to enhance the understanding of fracture mechanism of rock with respect to high temperature treatment and provide guidance in the analysis and design of deep underground engineering application.