Experimental investigation on physical and mechanical properties of granite under high temperatures thermal cycles

Abstract

Abstract In this study, the physical and mechanical properties of granite after tenth cycles at 25–450℃, combined with scanning electron microscope observation, the development and expansion laws of internal fractures in granite under different temperature cycles, and the relationship among P-wave velocity, porosity, permeability, uniaxial compressive strength (UCS), elastic modulus (E) and peak strain have been established by regression analysis. The experimental results show that the P-wave velocity of granite reduces the fastest in the first third cycle, which decreased by 10.27%, 21.44%, 31.08%, and 41.35%, respectively. The porosity and permeability showed a logarithmic increase trend with the increase in temperature; the porosity and permeability increased logarithmically with the increase of cycle temperature and stabilized after 5 cycles. With the increase in cyclic temperature, the UCS and E of granite decrease. After ten cycles, UCS decreased by 28.84, 34.37, 40.95, and 45.53%, and E decreased by 19.45, 32.18, 44.92, and 49.01%, respectively. The longitudinal wave velocity is fitted with porosity, permeability, uniaxial compressive strength, E, and peak strain, and it is found that they all show a high correlation. The P-wave velocity has a logarithmic relationship with porosity, permeability, and peak strain and a power function relationship with UCS and E. The experimental results reveal the deterioration mechanism of physical and mechanical properties of geothermal energy mining. The physical and mechanical properties of granite can be inferred by measuring the P-wave velocity, which has a specific guiding significance for geothermal energy mining.