Failure assessment of underground tunnels

The increasing development of the world has demanded the construction of underground tunnels for needs such as transport, water supply, sewerage and telecommunication. As many of underground tunnels were constructed sometime in the last century or earlier, in most cases their condition has deteriorated mainly by weathering of rocks, corrosion of reinforcement and/or degradation of concrete. Consequently, the leaks have become a common problem in these assets and management of these aging infrastructures have become a pressing issue for asset managers. The current study identifies major failure mechanisms of underground tunnel and how such failures can be assessed. The study reveals that the ground water flow can be the major driver for commonly identified failure mechanisms of underground tunnels. Several failure mechanisms, extending from soil/rock failure to the concrete lining material failure, along with their corresponding failure criteria will be identified. The identification of such failure mechanisms can be helpful when characterising the limit state functions for the structural reliability assessments. An example is provided to demonstrate the proposed methodology for assessing the structural reliability of aging tunnels. The proposed failure assessment method can help the infrastructure managers to develop rehabilitation or replacement strategy for in-service tunnels with a view for optimum maintenance management of the tunnel assets.