<p>To elucidate the instability mechanisms of surrounding rock in water-rich tunnels under construction disturbances, this study conducted triaxial graded cyclic loading–unloading seepage coupling tests to systematically investigate the mechanical response and permeability evolution characteristics of saturated sandstone. The results demonstrate that cyclic loading induces multi-crack failure patterns, distinct from the conventional single shear plane failure. Increasing confining pressure promotes a transition from tensile cracking to shear-dominated failure, while elevated seepage pressure induces tension-shear composite failure. The morphological evolution of hysteresis loops characterizes the damage transition from primary fracture closure to new crack propagation. Under cyclic loading–unloading, the post-peak permeability increases by one order of magnitude on average compared to the initial permeability. The crack volumetric strain transitions continuously from compression to dilation during loading, with its critical zero-crossing point under high confining pressure synchronously corresponding to the peak total volumetric strain and the inflection point of accelerated permeability increase. Elevated confining pressure transforms the loading permeability curve from “spoon-shaped” to “U-shaped” and delays the permeability inflection point. Under rapid loading rates, permeability is comprehensively reduced due to delayed seepage response. Increased seepage pressure enhances permeability by reducing effective stress and intensifying hydraulic gradients, resulting in significant permeability enhancement and accelerated post-peak fracture propagation. This research reveals the synergistic evolution mechanism of damage and permeability in sandstone under coupled graded cyclic loading-seepage effects, providing a theoretical basis for stability control of surrounding rock in water-rich tunnels.</p>