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To explore the mechanical properties and damage characteristics of basalt under high temperature and high pressure, triaxial compression tests are conducted on thermal damage rock samples, and the evolution process from progressive damage to macroscopic failure of rock is tracked and quantified by CT image reconstruction and acoustic emission technology. The results show that: (1) the ability of basalt to resist load and deformation changes from slight enhancement to rapid deterioration with the increase of temperature, and 600 ℃ is its threshold. The failure mode of rock gradually changes from brittleness to plasticity with the increase of temperature, and its post-peak stress gradually presents certain plastic flow characteristics. (2) With the increase of temperature, the initial damage variable D0 of basalt presents a stage feature of changing from low-speed development to rapid growth. When the temperature exceeds 400 ℃, the total damage variable D will have obvious precursor characteristic of small increase before the drastic change, and this characteristic will become more obvious with the increase of temperature. (3) The main mineral types of basalt hardly change with the increasing temperature, while the temperature has a certain influence on the proportion of some components. The proportion of anorthite and enstatite shows the changing trend of first decreasing and then increasing, while the evolution of andesine is opposite, and the proportion of other mineral components is basically unchanged. (4) The main reason for the improvement of mechanical properties of basalt within the temperature threshold is that the expansion of mineral particles and the constraint of confining pressure promote the closure of internal primary cracks and increase the compactness. However, when the heat treatment temperature of basalt exceeds the threshold value, the structural deterioration caused by heat treatment is gradually prominent, and the defects generated play a leading role in the mechanical properties of rock. Highlights: The mechanical properties of thermal damage basalt under triaxial loading were clarified and its temperature threshold was obtained The evolution process from progressive damage to macroscopic failure of basalt was tracked and quantified The microscopic failure mechanism of thermal damage basalt was revealed The number of tensile cracks of saturated coal increased with the cyclic loading frequency due to the prominent lag effect of strain behind stress. [ABSTRACT FROM AUTHOR]

Rockburst is a safety problem that needs to be solved urgently in deep rock and mineral exploitation. The stress gradient is an important factor affecting rockburst. To explore the influence mechanism of stress gradient on rockburst, the loading and unloading tests of rockburst physical model under different stress gradients are carried out using the self-developed gas–liquid composite rockburst test device. Based on the strain test results of rockburst model, the spatial distribution characteristics of elastic energy are analyzed. The particle size distribution characteristics and throwing kinetic energy of debris after the rockburst of model are studied. The following conclusions are obtained: (1) the value of the stress gradient coefficient m reflected by the strain within the range of the model loading rockburst gradient 1 affects the temporal and spatial distribution of energy release process; (2) With the increase of the vertical loading stress gradient, the rockburst debris gradually changes from large plate debris to small flake, block and powder debris. The maximum ejection distance of rockburst debris gradually increases, and the dynamic failure phenomenon of rockburst becomes more and more obvious; (3) As the loading stress gradient increases, the throwing kinetic energy of rockburst debris per unit mass shows an increasing trend. The research results are of great significance to tunnel safety construction and rockburst early warning. Highlights: The stress gradient is an important factor affecting rockburst in deep rock mass engineering. The value of the stress gradient coefficient affects the temporal and spatial distribution of energy release process. As the loading stress gradient increases, the rockburst debris gradually changes from large plate debris to small flake, block and powder debris. With the increase of the stress gradient, the maximum ejection distance of debris gradually increases, and the dynamic failure tends to be severe. [ABSTRACT FROM AUTHOR]