Mechanical Behavior and Deterioration Mechanism of Sandstone Under Acidic Wetting–Drying Coupling Effects

Abstract

Acidic wetting–drying cycles can progressively deteriorate sandstone used in rock engineering, but the link between macroscopic mechanical degradation and three-dimensional pore-crack evolution remains unclear. The objective of this work was to clarify the deterioration mechanism of sandstone under repeated acidic wetting–drying action. Sandstone specimens were subjected to 0, 5, 10, 20, or 30 wetting–drying cycles in a H2SO4 solution with an initial pH of 2.00. Triaxial shear testing, micro-CT reconstruction, scanning electron microscopy, and a correlation analysis were combined to characterize changes in the mechanical behavior and microstructure. With an increasing cycle number, the cohesion and internal friction angle decreased by 40.85% and 11.27%, respectively, while the pore network became progressively enlarged, connected, and structurally complex. The pore fractal dimension increased from 2.18 to 2.49. Scanning electron microscopy images showed enlarged pores and cracks, looser particle contacts, and local damage along particle boundaries. Increasing the confining pressure improved the peak resistance and restricted crack development. A correlation analysis indicated that mechanical degradation was closely associated with the evolution of the pore and crack structure. These results establish a multiscale relationship between the loss of mechanical performance and microstructural deterioration, providing a basis for evaluating sandstone stability in acidic environments.