Softening properties and damage evolution of the preloaded building sandstone after exposure to high-temperature

Abstract

In practical engineering, cyclic stress caused by underground excavation, blasting or seismic waves leads to initial damage to rocks, and the high temperature caused by fire will lead to changes in the mechanical and physical parameters of the initially damaged rock. Therefore, a series of experiments were carried out to research rock properties and damage evolution of the preloading sandstone after exposure to high temperatures. The results demonstrate that the mass decreases gradually at a constant rate when the temperature ranges from 25 °C to 600 °C, but above 600 °C, the quality decreases quickly. As the exposed temperatures and stress amplitude of cyclic preloading rise, the p-wave velocity gradually decreases. At exposure temperatures of up to 800 °C, the p-wave decreases by 27.8%, and it is reduced by 0.93% at the largest pre-stressed condition. Furthermore, the peak strength and elastic modulus decrease with the rise of the preloading stress amplitude and treated temperatures. The area of hysteresis loops increases with the increase of the cyclic preloading stress amplitude, and the plastic deformation of hysteresis loops results in the continuous deterioration of the secant modulus. The preloading stress amplitude and the temperature gradually increase, and the damage factor increases. Meanwhile, to compare the performance of the proposed damage model, the constitutive damage model of the preloading treatment sandstone exposure to high temperatures is established. The model has a good fitting effect for the sandstone subjected to the thermal-mechanical effect.