Multi‑scale Experimental Investigations on the Deterioration Mechanism of Sandstone after high-temperature treatment

ABSTRACT: A significant aspect influencing engineering stability in deep engineering is temperature. In order to explore the influence of high temperature on sandstone, This study used experimental samples of sandstone from Shaanxi, China. Sandstone samples were subjected to varying temperature gradients (25℃, 100℃, 300℃, 500℃ and 700℃) for Uniaxial Compressive Strength (UCS), Acoustic Emission (AE) monitoring, and Nuclear Magnetic Resonance (NMR) experiments. The resulting mechanical parameters and pore diameter distributions of the sandstone under various temperatures were compared and analyzed. The results showed that: Peak strain and peak stress of sandstone samples both greatly rise and decrease with increasing heating temperature. The degree of elastic modulus and peak stress degradation is also more pronounced at higher temperatures. The brittle-ductile transition occurs at about occurs between 500°C~700°C. At temperatures between 25°C and 500°C, the peak AE energy occurs near the peak strength of the sandstone. The ringing counts of the sandstone specimens reached a maximum after the peak stress when the temperature was 700°C, and the peak AE energy gradually decreased at higher heating temperatures. The T2 spectrum curve and pore size curve of the sandstone increased and gradually shifted to the right with the increase of the treatment temperature, and the area of the T2 spectrum and porosity also gradually increased. There is a negative correlation between porosity and total area of T2 spectrum and peak stress and elastic modulus of sandstone under high temperature. The micropores showed a monotonically decreasing trend with increasing temperature