Damage and fracture evolution in basalt under thermal effect with constitutive model development

Microwave-assisted rock breaking has the advantages of green and low energy consumption, and it is expected to be a technical means to achieve efficient excavation of hard rock strata in underground development. To explore the whole process of progressive failure of basalt after different temperatures, uniaxial compression tests were carried out on basalt at 25℃, 200℃, 400℃ and 600℃, and the acoustic emission phenomenon in the whole deformation process was monitored. The thermal damage constitutive model considering the coupling of initial thermal damage and mechanical damage was optimized by using nonlinear stage correction and damage correction factor. The analysis results show that the stress-strain curve characteristics of rocks are significantly affected by temperature. With the increase of temperature, the uniaxial compressive strength and elastic modulus of basalt decrease, and the compaction stage of the curve becomes longer. As the temperature increases, the energy of rock sample is concentrated in time and released instantly before the rock debris collapse. Before 400℃, it is mainly the change of water content in basalt. When the temperature exceeds 600℃, micro-defects emerge due to mineral expansion, phase transition, transformation, recrystallization and melting. In addition, the stress-strain constitutive model of basalt in the whole deformation process is derived according to the axial strain law of cracks and acoustic emission parameters. The calculated results of the model are in good agreement with the experimental curves, which can be used to study the failure process of rocks under high temperatures.