Journal of Rock Mechanics and Geotechnical Engineering (Aug 2020)
Physico-mechanical properties of granite after cyclic thermal shock
Abstract
Understanding rock mechanical behaviors after thermal shock is critically important for practical engineering application. In this context, physico-mechanical properties of Beishan granite, Gansu Province, China after cyclic thermal shock were studied using digital image correlation (DIC), acoustic emission (AE) monitoring, and microscopic observation. The results show that the peak strength and elastic modulus decreased gradually with increase in thermal shock cycle. However, the above two parameters showed no further changes after 10 thermal shock cycles. The loading stress ratio (i.e. the ratio of the current loading stress level to the peak stress in this state) corresponding to the occurrence of the uneven principal strain field and the local strain concentration zone on the surface of the granite specimen decreased with increase in thermal shock cycle. Three transformation forms of the standard deviation curves of the surface principal strain were found. For granite with fewer thermal shock cycles (e.g. no more than 2 cycles), the standard deviation curves exhibited approximately exponential growth in exponential form. With increase in thermal shock cycle, the S-shaped curve was dominant. After 10 thermal shock cycles, an approximate ladder-shaped curve was observed. It is displayed that AE activity was mainly concentrated around the peak strength zone of the granite specimen when the rock samples underwent fewer thermal shock cycles. With increase in thermal shock cycle, AE activity could occur at low loading stress levels. Microscopic observation further confirmed these scenarios, which showed that more microcracks were induced with increase in thermal shock cycle. The number of induced microcracks at the edge location of the granite specimen was significantly larger than that at the interior location. Finally, a continuum damage model was proposed to describe the damage evolution of the granite specimen after cyclic thermal shock during loading.
