Hydro-induced large deformation and control of tunnels in silty weathered tuff: a case study of the Liren Tunnel

Abstract

Severe large-deformation hazards, including support cracking and face instability, occurred at the Liren Tunnel entrance, which traverses complex composite strata of weathered tuff and silty soil. This study investigates failure mechanisms under coupled hydro-induced deterioration and engineering disturbances. Laboratory tests quantified significant water-induced strength attenuation in both the tuff skeleton and silt filler, revealing a superimposed weakening mechanism that drastically reduces stratum bearing capacity. FLAC3D simulations integrated these parameters, confirming groundwater as the core trigger (increasing displacement by 80%) compared to the dry state, while inadequate construction methods amplified deformation. Consequently, a targeted combined control technology comprising an optimized three-bench method with reserved core soil, composite advance support, and strengthened primary support was implemented. Field monitoring validated this solution, reducing crown settlement by approximately 50% and shoulder convergence by 70%, effectively preventing further failures.