Deterioration Damage Characteristics of Rhyolite under Cyclic Immersion of Hydrochemical Solutions

The tunnel surrounding rock in water-rich regions is subjected to long-term chemical corrosion and cyclical water immersion erosion. In order to investigate the damage mechanisms of chemical corrosion and cyclical water immersion on rock masses, a 60-day cyclical water immersion test was conducted on sandstone specimens under simulated water chemistry environments with different pH values (7, 5, 3) and flow velocities(0, 300, 900 mm·s^-1). The degradation and damage mechanisms of rock mechanical parameters were analyzed through triaxial compression tests and techniques such as scanning electron microscopy, digital image correlation, and XRD diffraction experiments. The results reveal that: (1) Lower pH values and higher flow velocities in the chemical solution are associated with greater microstructural damage, porosity increase, attenuation of elastic wave velocity, internal friction angle reduction, and cohesive strength decline in the sandstone specimens. (2) In the triaxial compression tests, the failure mode of the sandstone specimens under pH=7 environment is mainly shear slip failure, while under pH=5 and 3 environments, columnar splitting failure is prominent. The globally distributed strain fields and localized deformation bands coincided with the location of failure, with higher flow velocities corresponding to larger strain values in the specimens. (3) During the initial stage of water immersion testing, the mass loss factor and degradation rate of elastic wave velocity decreased gradually over time. (4) Under constant flow velocity, the peak strength and maximum volumetric strain of sandstone increased with increasing confining pressure, while under constant confining pressure, they decreased with higher flow velocities.