Analysis of squeezing‐induced failure in a water tunnel and measure of rehabilitation: A case study of Tishreen tunnel, Syria

Squeezing phenomena can lead to severe loads in deep tunnels, especially in the presence of a low ratio of surrounding rock strength to overburden pressure. For this reason, it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass. This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service. The tunnel in question was subjected to successive failures such as buckling and spalling of side walls, floor heave, and extremely large convergence reaching the failure state of the tunnel lining. In this study, an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long‐term response of a tunnel excavated in weak rock. Specifically, the causes of failure of Tishreen tunnel were first evaluated by empirical approaches. Then, a numerical model was developed using a time‐dependent constitutive model to investigate the time‐dependent response of the tunnel lining. On this basis, this study proposed an effective reinforcement schemes including steel ribs, grout injection, ground anchors, and new lining of reinforced concrete. The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground. It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study. Tunnel lining can suffer from excessive convergence and floor heave due to the squeezing deformation in the long term. The Burger–creep viscoplastic model represents an efficient constitutive model for describing the tunnel response associated with squeezing conditions. A rigid support system is proposed and verified as a powerful tool for controlling squeezing deformation in deep tunnels.