Numerical simulation and treatment methods for a collapsed highway tunnel

NATM (New Austrian Tunneling Method) has been widely used in many countries for tunnel construction. The main feature of NATM is to utilize all available means to develop the maximum self-supporting capacity of the surrounding rock or soil itself, and to undertake investigation and monitoring during construction to provide the stability of the tunnel. If undetected worse ground condition is encountered, the strengthening works will be carried out to ensure safety. This paper presents and reviews the cave-in collapse in Wangkeng tunnel. Collapse of tunnel face and sinking of upper ground happened from YK49+575 to YK49+610 during construction. The 35 m of collapsed tunnel crown affected 50 m of tunnel. The treatment methods including ground grouting, pipe roof reinforcement and partial face excavation were then implemented and completed successfully. Stability of reinforced and unreinforced tunnel was evaluated by numerical simulation. The analysis results show that these treatments can satisfy the design requirements. It could be a useful reference to the design and construction of tunnels in similar formations.