To investigate the effects of impact and static compaction methods on the mechanical properties and crack evolution of rock-like materials with varying particle sizes. Uniaxial compression tests combined with Digital Image Correlation (DIC) technology were conducted on specimens of two aeolian sand gradations (0.075–0.18 mm and 0.22–0.5 mm) and one quartz sand gradation (0.22–0.5 mm). The study focused on elastic modulus, peak strength, stress-strain behavior, failure modes, surface deformation fields, crack propagation paths, and strain evolution at characteristic points under both compaction methods. Finally, the microstructure of specimens was analyzed and compared with natural rock analogs. Key results include: (1) At an identical density of 1.82 g/cm³, static-compacted specimens of fine-grained aeolian sand (0.075–0.18 mm) exhibited higher elastic modulus and peak strength compared to impact-compacted counterparts, whereas inverse trends were observed for coarse-grained aeolian sand (0.22–0.5 mm) and quartz sand specimens; (2) Under equivalent compaction energy (254.8 J), the hierarchy of mechanical performance was: quartz sand > coarse-grained aeolian sand > fine-grained aeolian sand; (3) Static-compacted specimens predominantly failed through tensile splitting, while impact-compacted specimens exhibited shear-dominated failure modes; (4) DIC full-field strain mapping revealed rapid propagation of primary cracks along pre-existing weak planes in static-compacted specimens, forming through-going tensile fractures. In contrast, impact-compacted specimens developed fractal strain field structures with coordinated evolution of shear bands and secondary tensile cracks; (5) Microstructural comparisons showed that static-compacted fine-grained aeolian sand specimens exhibited root-like structures with high porosity, resembling weakly consolidated sedimentary rocks. Impact-compacted coarse-grained aeolian sand specimens displayed stepped structures with dense packing, analogous to strongly cemented sandstones.

Water saturation is a key factor influencing the mechanical behavior and stability of tunnel rock masses in water-bearing strata. However, current research based on physical model tests has yet to systematically reveal its intrinsic relationship with rock failure modes. To address this gap, this study systematically investigated the effects of water saturation levels (0%, 33%, 58%, and 100%) on the failure mechanisms of four typical tunnel cross-section models: wall-arch, horseshoe, circular, and square. The results indicate the following: (1) Water saturation exerts a significant deteriorating effect on the mechanical properties of tunnel models. As saturation increases, peak stresses generally decrease across all models, but the extent of deterioration varies markedly by tunnel shape: at low saturation (≤58%), peak stress follows the order Wall-Arch > Horseshoe > Circular > Square; at high saturation (>58%), this relationship reverses to Circular > Square > Wall-Arch > Horseshoe. (2) The failure mechanism is significantly controlled by saturation, exhibiting distinct transition characteristics: At low saturation, capillary effects dominate, with matrix suction enhancing material strength, resulting in brittle failure with crack concentration. At high saturation, pore water pressure effects prevail, reducing effective stress and leading to plastic failure dominated by distributed shear slip. Notably, square tunnels consistently exhibit pronounced flexural failure characteristics across all saturation levels. (3) Energy evolution analysis indicates the following: as saturation increases, the total energy U of specimens decreases, the dissipation rate of dissipated energy U_d accelerates, the energy inflection point advances, and failure precursors manifest earlier. The energy dissipation factor n of high-saturation specimens decreases more significantly with increasing strain, confirming that moisture accelerates energy dissipation and promotes premature material instability. (4) Significant differences exist in the response characteristics to moisture effects among tunnel types: Square tunnels consistently exhibit pronounced flexural failure; Circular tunnels demonstrate optimal stress distribution properties under high water content conditions; Wall-arch and horseshoe-shaped tunnels are most sensitive to saturation changes, with their failure modes transitioning from tensile-dominated to shear failure as water content increases. This study reveals the coupled mechanism between water saturation and tunnel cross-sectional shape in influencing rock mass stability.