Effects of high temperature and acidic solutions on the pore characteristics and mechanical properties of sandstone

Sandstone is a common construction material widely distributed in mountain tunnels. Its stability determines the safety and service life of tunnel projects. The surrounding rock of the tunnel is subject to frequent fire incidents and long-term erosion by acidic groundwater throughout its entire life cycle. This study investigated the pore characteristics and mechanical properties of sandstone under different high temperatures and acidic solutions. The T2 spectrum distribution, pore size distribution, porosity, compressive strength, and elastic modulus of sandstone were observed through uniaxial compression tests and nuclear magnetic resonance (NMR) tests. The results showed that high temperature and acidic solutions significantly affected the T2 spectrum distribution, pore size distribution, porosity, compressive strength, and elastic modulus of sandstones, and their effects on the pore structure and mechanical properties of sandstone differed in each stage. The effect of high temperature on the pore structure and mechanical properties of sandstone was stronger than that of the acidic solutions. In addition, the mechanism of damage formation is characterized by the porosity variation of sandstone. The pore structure of sandstone showed a close linear relationship with mechanical properties, indicating that changes in microstructure inevitably affected the macroscopic mechanical properties of sandstone. These findings can guide the construction and repair of rock failure induced by fire and acidic groundwater, providing a reference for associated tunnel projects.