Mechanical Properties and Damage Evolution Characteristics of Thermal Damage Basalt Under Triaxial Loading

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.