Characterizing time-temperature coupled effects on mechanical-seepage properties of grouted rock mass in water-rich tunnels

To elucidate the influence of the coupling effect of a water-rich temperature environment and time on the mechanical properties of the grouted rock mass, we enhanced a self-constructed three-dimensional rock mass grouting simulation test device. Employing a uniform design method, five working conditions were established for conducting high-pressure grouting tests. A total of 270 standard cylindrical samples were prepared, with multi-gradient curing times ranging from 7 to 90 days in water-rich temperature environments, enabling a systematic investigation of the time-dependent evolution of compressive strength and permeability characteristics of the grouted rock mass. The findings demonstrate that the improved three-dimensional test system can accurately simulate the grouting environment of 20 ℃ to 60 ℃surrounding rock. Furthermore, a multi-field coupling physical test platform was successfully constructed, integrating temperature, seepage, and stress fields. The mechanical properties of the grouted rock mass exhibited a pronounced temperature threshold response. Specifically, the compressive strength in a 50 ℃ water-rich environment displayed a three-stage evolution characterized by peak-attenuation-stability over curing time, aligning with the Gaussian distribution law. After 28 days of curing, the influence of the water temperature factor surpassed that of the water-cement ratio and grouting pressure. Additionally, a double-critical transition phenomenon was noted in the permeability characteristics. The permeability coefficient in the 50 ℃ water-rich environment adhered to a cubic polynomial trend, while in the 60 ℃ water-rich environment, the 28-day curing time served as a turning point, resulting in abnormal permeability changes in the later stages, transitioning from continuous reduction to linear growth. Under the 60 ℃ water-rich conditions, a significant negative correlation was observed between compressive strength and permeability, with the two trend curves exhibiting two cross-turns. This observation revealed the deterioration mechanism linked to thermal damage accumulation and micro-fracture network evolution in the grouted rock mass due to the synergistic effects of water-rich temperature, seepage, and time. By transcending the traditional limitation of a 28-day curing period, the derived evolution law regarding the performance of the grouted rock mass, based on the dynamic water-rich temperature-time threshold, provides a theoretical foundation for optimizing grouting times in deep-buried tunnels and ensuring the long-term stability of surrounding rock.