Time-Dependent Squeezing Deformation Mechanism and Its Active Control Method of Deep Soft-Rock Tunnels Crossing Thrust Faults

The engineering activities of deep-buried tunnel crossing active faults in western China are becoming increasingly frequent, and the large deformation of squeezing rockmass has become a core technical problem of tunnel construction. Compared to general large deformation disasters, the surrounding rock in deep fault fracture zones has a more significant time-dependent deformation mechanism, leading to severe structural cracking and instability disasters in tunnels. However, current engineering practices mainly emphasize the passive bearing role of supporting structure system, often neglecting the necessity of actively controlling the deformation of surrounding rock in complex geological environments. This paper aims to investigate the time-dependent deformation mechanism of deep soft-rock tunnels crossing thrust faults, and propose the reasonable active control methods for squeezing large deformation. Firstly, based on the Burger’s creep model, a discrete element model is established to examine the time-dependent deformation behavior of the surrounding rock. Following this, the damage behaviors promoted by traditional passive support and double-layer primary support methods are studied. Further, in-depth research is conducted on the grouting reinforcement mechanism of deep strata and the corresponding deformation control effect of surrounding rock. Finally, an active deformation control method with collaborative supporting system is proposed and applied to a broken phyllite tunnel crossing thrust faults. The results indicate that in deep tunnels crossing active faults, the increase in surrounding rock pressure and deformation over time is mainly due to the aging deterioration behavior of deep fractured rockmass under high stress conditions. The use of conventional passive supporting structural systems and optimization of supporting timing cannot effectively suppress the time-dependent fracturing of surrounding rock, leading to the expansion of loosening zones and lining cracking problems. The implementation of the multi-layer supporting structures and grouting bolt reinforcement method markedly enhance the structural integrity and bearing strength of the deep rockmass. This active deformation control method with collaborative supporting system effectively reduces the maximum deformation and number of cracks by 75% and 94%, respectively. The proposed active time-dependent deformation control method, combined with on-site engineering applications, provides an effective strategy for deep soft-rock tunnels crossing thrust faults.