Mechanical characteristics and energy evolution law of sandstone failure process under post-peak cold and heat cycle

Abstract

In coal fire control, grouting/water extinguishing is often repeated for reasons such as re-ignition. The surrounding rock undergoes repeated heating and water cooling, resulting in strength reduction and damage, and collapse and cracks on the extended surface, resulting in potential safety hazards. Therefore, the change of rock mechanics under high temperature and cold cycle after peak is studied. Taking sandstone as the research object, the ultrasonic wave velocity and water absorption rate of rock samples were tested, and the uniaxial compression test was carried out. The mechanical damage characteristics of sandstone were analyzed, and its energy consumption evolution law was further explored. The results show that: from 500 ℃ after the peak, the attenuation rate of ultrasonic wave velocity and the change rate of water absorption of rock samples change from positive to negative, the wave velocity decreases and the water absorption increases; 500 ℃ is the threshold temperature of mechanical sudden change of high-temperature rock sample after the peak, and then the peak point of stress-strain curve moves rapidly to the right, the peak stress declines greatly, and the initial thermal damage caused by cold and hot cycles intensifies, and the ductile failure is obvious; the evolution characteristics of energy consumption are different in different stages of rock samples under pressure. From 500 ℃ after the peak, the proportion of dissipated strain energy before the peak is gradually larger than that of elastic strain energy, and the dissipated strain energy is negatively correlated with the mechanical strength.

Keywords

• coal field fire
• cooling-heating cycle
• thermal damage
• mechanical properties
• energy evolution