Macro-meso deterioration characteristics and statistical damage constitutive model for acid-corroded sandstone

Long-term hydrochemical corrosion leads to mineral dissolution, meso-structure change, and further mechanical deterioration of rock. This paper studied the effects of pH = 1, 3, 5 HCl solutions and pH = 7H2O on sandstone damage from macro-meso perspectives. The mesostructure from different corroded parts was fine analyzed, and the sandstone porosity was calculated by CT (Computed Tomography) image processing techniques. The mechanical properties and energy evolution laws under uniaxial compression were investigated. The full deformation of sandstone was theoretically analyzed, and the damage constitutive model considering initial compression was developed and verified. The results showed that after acid corrosion, more pores and microcracks occurred in the sandstone, the mesostructure became loose, and the calculated porosity based on CT images can represent the actual sandstone porosity. The yield stress, peak stress, and elastic modulus declined, and the peak strain improved. The energy storage capacity weakened, and the plastic deformation before the peak point increased. The effects were more evident with the acidity and immersion time. The acid-corroded sandstone was abstracted into two portions: the initial voids and the solid skeleton. The initial voids deformed nonlinearly in the compaction stage, and the solid skeleton deformed linearly before yielding and nonlinearly after yielding. The theoretical curves of the constitutive model for acid-corroded sandstone agreed well with the experimental ones, which verifies the model is reasonable.