Hot dry rock is developed by injecting cold water into high-temperature rock mass. At the same time, cold water is heated in contact with the rock mass. With the continuous influx of cold water, the surrounding rock will undergo a rapid cooling process, which results in several cycles of heating and cooling. However, there is little research on the influence of cycles of heating and cooling with circulating water on the mechanical properties of rock, which is of great importance to the stability of rock mass engineering in the process of energy development. In this paper, the effects of cyclic heating and cooling with circulating water on the damage of granite are studied using uniaxial compressive, Brazilian and acoustic emission (AE) tests. The results show that heat treatment temperature and number of cycles have important effects on the mechanical properties of granite as follows: (1) at the same treatment temperature, an increase in the number of cycles means that the distribution of physical and mechanical parameters of the granite show an almost exponential downward trend. The uniaxial compression of granite results in its transformation from brittle to plastic, and the failure mode changes from slipping of the shear surface to plastic failure. With increased cycles of heating and cooling with circulating water, the tensile strength of granite also decreases; temperature has an obvious influence on physical and mechanical parameters, cracking of samples, and plays a controlling role in the failure mode of samples. In addition, (2) at the same temperature, the heating and cooling numbers N have a significant influence on the AE distribution characteristics of the sample under uniaxial compression and the number of AE collisions, and the cumulative number of AE decreases with the increase of N. (3) The concepts of mechanical damage and high-temperature and cold-water shock damage during uniaxial compression of samples were proposed based on AE, and the damage equations were established respectively. The curve equations of damage value (D) and cycle numbers N after thermal shock damage of high temperature and cold water were overlaid. The cracking mechanism of high-temperature and cold water impact on granite was analyzed, and the thermal shock stress equation of high temperature and water cooling was established.

This study experimentally analysed the influence of temperature levels (200, 300, 400, 500, 600, and 800 °C) on the permeability of granite samples. At each temperature level, the applied confining pressure was in the range of 10–30 MPa, and the inlet hydraulic pressure varied below the corresponding confining pressure. The results are as follows: (i) With an increase in the temperature level, induced micro-fractures in the granites develop, and the decrement ratios of both the P-wave velocity and the density of the granite increase; (ii) The relationship between the volume flow rate and the pressure gradient is demonstrably linear and fits very well with Darcy’s law. The equivalent permeability coefficient shows an increasing trend with the temperature, and it can be best described using the mathematical expression K₀ = A × 1.01^T; (iii) For a given temperature level, as the confining pressure increases, the transmissivity shows a decrease, and the rate of its decrease diminishes gradually.

The mechanical properties and anchorage performances of rock masses are important to the success of underground engineering in fault fracture zones, but the impact of the rock block size and cementing strength on these properties and performances is unclear. A set of laboratory methods was developed to simulate the development of rock masses in fault fracture zones. Next, model specimens were prepared from natural rock blocks of different sizes and cementing materials of various strengths, and an aluminum alloy bar was installed as a model bolt to fabricate anchored model specimens. Compared with natural rock samples, the fault fracture rock mass exhibited a clear degradation in its strength and deformation parameters, and the degradation coefficients ranged from 19.20 to 86.51%. Under an applied axial load, as the rock block size or cementing strength increased, the mechanical parameters, including peak strength and elastic modulus, for both anchored and nonanchored model specimens increased from 16.90 to 69.05%. Because of the anchorage performance of the bolt, the anchored model specimens presented larger mechanical parameters than those of the nonanchored models. The effective anchorage strength of the bolt was found to be generally stable as the rock block size increased, but it decreased with the cementing strength. The ultimate failure modes of the anchored models with smaller aggregate sizes or lower cementing strengths were found to be characterized by cracks propagating along the cementing surface. For models with a larger rock block size or higher cementing strength, crack development throughout the intact rock blocks was also observed.