Influence of Strain Rate on the Physical–Mechanical Characteristics and Pore Structure of Sandstone in the Shanxi-Tong Chuan Reservoir Region Subjected to Sulfate Attack

The fracture toughness (KIC) of Mode I cracked sandstone exposed to sodium sulfate was investigated in this study. The uniaxial behavior of sandstone specimens soaked in different sodium sulfate solutions was determined for different strain rates. The results revealed that the strain rate has a significant and positive influence on the deformation and strength characteristics of sandstone. Compression strength gradually increased with strain rate at an increased slope, but peak strain decreased gradually with an increase in strain rate. The physical–mechanical characteristics and brittleness of sandstone gradually declined with increasing immersion time under sodium sulfate attack, but its plasticity increased significantly. There were holes and pitting corrosions in specimen surfaces exposed to sodium sulfate attack, and the edges and corners were somewhat weakened. Chemical damage variables were proposed to analyze the damage degree of sandstone, based on the change in porosity. Based on the testing results, regression analysis was conducted to determine the relations between ion concentrations (Ca2+ and Mg2+) in corresponding sodium sulfate solutions and for corresponding degrees of damage, and indirectly realize correlations between physical–mechanical characteristics, damage degree, and ion concentration.