Risk-cost optimised maintenance strategy for tunnel structures

Due to limited maintenance budget, effectively spending the available funds for maintaining infrastructures is increasingly sought by asset managers. Tunnel is an essential infrastructure that plays a pivotal role in transportation network, economy, prosperity, social well-being, quality of life and the health of its population. In the light of considerable research that has been or is being undertaken on "aboveground" infrastructure, e.g. bridges, this threat cannot be more apparent for underground infrastructure such as tunnels. The situation has been exaccrbatcd due to more unknowns and uncertainties relating to the factors such as underground water and soil/rock that affect the operation of tunnel infrastructure. In an ageing tunnel system, various potential deficiencies such as seepage, spalling, crack, delamination, steel corrosion, drainage, convergence and settlement of the lining structure can cause catastrophic life safety and economic consequences. Most collapses of tunnel structures in the world are related to tunnel deterioration with catastrophic consequences. Through an effective maintenance plan, the catastrophic failures of tunnels can be prevented. This research aims to develop a maintenance strategy for concrete tunnels which determines when (maintenance intervention times), where (segments of tunnel network) and what (failure mode of tunnel structure) maintenance actions need to be taken to ensure the safe and serviceable operation of tunnel with the intention to minimise the risk. The mathematical formulation of the proposed maintenance strategy, which is based on risk optimisation, is provided in a generic format. Application of the proposal to tunnel structures is presented in a numerical example.