Damage behaviour of sandstone induced by combination of dry-wet cycles and acidic environment

Mine-water infiltration and ventilation drying during coal mining have a considerable effect on the stability of the surrounding rock, especially when the mine water is acidic. In this study, a dry-wet cycle test is first conducted to simulate the rock-fluid interaction, and the mechanical properties of sandstone during the acidic dry-wet cycle are studied. Thereafter, a comprehensive method combining nuclear magnetic resonance, X-ray diffraction, and scanning electron microscopy techniques is established for chemical damage analysis, and the damage mechanism of sandstone is summarised. The test results reveal that as the number of cycles increases, the spectral area and porosity always increase, peak strain increases, and peak strength decreases. At higher acidity, the pore-shifting trend is much more noticeable. With the increase in acidity, the minerals in the rock sample react violently with H+, resulting in a steady increase in the number of pores and fissures. The damage in the surrounding rock can be attributed to the accumulation and coupling of multiple physical and chemical water-rock interactions. Porosity is utilised as an index of rock damage. The functional relationship between the number of drying-wetting cycles and the damage magnitude is established by analysing the quantitative relationship between porosity and rock damage. This provides useful insights into subsequent quantitative research on rock damage.