Experimental study on the variation of wave velocity and resistivity of limestone under heating temperature and cooling condition within 200 °C

Understanding the variation patterns of physical and mechanical properties of rock under heating and cooling conditions is crucial for predicting and evaluating the stability of deep engineering works, such as nuclear waste storage and geothermal energy production. In this paper, limestone is heat-treated at temperatures ranging from 20 to 200 °C, and variation patterns of P-wave and S-wave velocities as well as resistivity of limestone under heating temperature and cooling condition are comparatively analyzed. The results confirm that the wave velocity decreases approximately linearly with the increasing temperature, with a greater decrease under heating temperature condition. The resistivity of limestone decreases first and then rises sharply under heating temperature condition, while it gradually increases under cooling condition. The differences in thermal expansion of minerals and degree of internal micro-crack expansion after two different treatments primarily contribute to different variation laws of P-wave and S-wave velocities. Water content, conductive ionic activity, and thermal cracks under two different temperature conditions jointly affect the resistivity of limestone. The findings of this study are anticipated to offer theoretical support for rock mass engineering in high-temperature environments, particularly in evaluating the stability of reservoirs before and after hot dry rock heat extraction.