Macro- and meso- shear mechanical properties of rock-grout composite structures under different stress level and initial hydration damage

This study investigates the shear mechanical behavior of soft rock-grout coupled structures through triaxial shear tests and particle flow simulations on sandstone-resin composite specimens under varying normal stresses and immersion times. Key findings include: (1) Intensified hydration damage compromises shear resistance in both rock and interfaces, amplifies deformation, and degrades bearing capacity. (2) Elevated normal stress constrains microcrack coalescence, enhances bearing capacity. Failure modes of specimens-classified as interfacial shear sliding, mixed shear failure, or shear failure occurs exclusively within rock-depending on stress levels and hydration duration. (3) Prolonged immersion reduces energy thresholds for bond rupture, shifting crack propagation from abrupt surges to gradual increments. Weak zones migrate from interfaces to external rock. (4) Increased normal stress raises energy storage limits, suppresses microcrack coalescence, and strengthens weak zones. This study revealing the critical control of hydration damage and stress confinement on energy thresholds at the rock-grout interface, providing a theoretical basis for long-term stability prediction of anchorage structures.