The thermo-mechanical (TM) coupling effects of rock masses and rock bursts have attracted great attention among researchers due to high geothermal and geo-stresses in deep tunnels in Western China. In order to study the brittleness and rock burst characteristics under TM conditions, various tests were carried out at temperatures ranging from 20 to 80°C. The results show by increasing the temperature of granite samples, their tensile strengths were decreased, post-peak stresses were dropped, and macroscopic tensile fracture surfaces became more obvious. The microcosmic tensile properties of intergranular fractures were prominent. The results obtained from rock burst physical models and acoustic emission monitoring tests showed that at higher temperatures, fracture degree and failure range of the model were larger, energy was higher and more concentrated during failure, and failure occurred earlier. Brittleness index B, Wet index and σθ/σc all showed obvious increasing trends with the increase of temperature.
The mechanical characteristics of rocks in deep complex environments have become a popular topic among researchers in recent years. Under deep buried environment, surrounding rocks may be exposed to high temperature and high stress condition. Complete and hard rock masses are prone to brittle failure, inclding spalling (Zhou et al., 2014), tensile (Andersson, 2007), and even rock burst failures, as shown in Figure 1. Therefore, it is extremely urgent to study the brittleness and rock burst temperature effects of hard rocks under high ground temperature and stress conditions.
Brittleness is the impending destruction of materials under small deformations and is an important indicator in rock burst prediction. So far, many researchers have provided rock brittleness evaluation indices (Baron, 1962, Bishop, 1967; Hucka & Das, 1974; Altindag, 2000). For example, Tarasov and Potvin (2013) proposed a brittleness evaluation index B1 for energy evolution during rock failure based on pre-peak dissipated and post-peak energies. and the most commonly used brittleness indices are B3-B7 which are based on rock uniaxial compressive strength and tensile strength proposed by Hucka & Das (1974) and Altindag (2000, 2008). Besides, temperature has a significant effect on the brittleness of rocks. Normally, under the action of heating, rock deformation and fracture mechanisms change due to the activation of rocks and fluid media. Rocks are prone to plastic deformations (Wang et al., 2008; Xu et al., 2008), and transitions from brittle to ductile or plastic failures (Zhang et al., 2014; Fang et al., 2016). Chen and Li et al. (2013).
