Abstract:
Permeable ribbed double-arch tunnels are susceptible to void formation behind the lining under complex loading and construction conditions, posing potential threats to long-term structural safety. Based on the Nanshan Tunnel Project, model tests and finite element numerical simulations were conducted to investigate the influence of voids at different locations behind the lining on the internal forces and complete evolution of cracking and damage in permeable ribbed double-arch tunnels. The results reveal that regardless of the presence of voids, cracks always appear first in the rib beams and eventually suffer the most severe damage; the void at the top of the middle wall is the critical factor triggering overall structural failure. This void weakens the supporting effect of the middle wall, resulting in a dramatic increase in negative bending moments at the left haunch of the inner tunnel, negative bending moments at the right arch foot of the outer tunnel, and positive bending moments at the right shoulder of the outer tunnel, and accelerates early cracking of rib beams due to the interruption of the synergistic supporting effect between the middle wall and rib beams; the void at the inner tunnel crown is the decisive factor causing the transformation of local stress patterns, shifting the crown lining from the conventional compression-bending state (tension inside, compression outside) to a reverse bending state (tension outside, compression inside), thereby inducing cracking on the outer surface of the lining; the void at the arch shoulder primarily manifests as a significant enhancement effect on local stress concentration, wherein the void at the left arch shoulder of the inner tunnel, due to its proximity to the middle wall connection area, produces a chain reaction similar to the void at the top of the middle wall, exacerbating the damage to the rib beams.