Monitoring and modelling the long-term performance of Dublin Port Tunnel
Dublin Port Tunnel, the biggest urban road tunnel in Ireland, functions as a critical part of an arterial road network between Dublin Port and the rest of Dublin city. Since its opening in 2006, the tunnel has been observed with progressively developing deteriorations; onsite observations and maintenance records have identified three main types, i.e., tunnel leakage, lining crack and concrete spalling, as the greatest engineering concerns to asset owners. The increasing structure deformation may disrupt tunnel operation, threaten tunnel serviceability, and/or even endanger tunnel integrity and safety in the long term. To better the understanding of the structural health condition of this critical underground infrastructure, this thesis specifically investigates the long-term ageing performance of a cross passage twin tunnel section of Dublin Port Tunnel subject to various deteriorations through an integrated assessment based on innovative field monitoring (i.e., wireless sensor network) and advanced numerical modelling (i.e., finite element modelling), where previous investigations mainly concentrated on the responses of a single tunnel section to short-term external disturbances (e.g., adjacent construction and surcharge). Characterisation of the selected deteriorated tunnel section on the basis of historical data, maintenance records, geotechnical and hydraulic reports is conducted first. Ground and tunnel parameters are obtained through applying theories and principles of soil and rock mechanics, followed by the determination of the current hydraulic permeability (conductivity) of the deteriorated section on the basis of monitored water flow. A modified analytical model for ground-lining relative permeability is proposed by assuming radial groundwater flow through all three ground layers and the hydraulic health status of the tunnel section is evaluated to be partially permeable. To quantitatively investigate the tunnel structural behaviour, an innovative wireless sensor network field monitoring system is adopted to monitor the long-term structural performance of the select cross-passage twin tunnel section, with the system’s reliability and robustness being tested inside an underground cave in the first place. The trial deployment of the wireless sensor network monitoring system inside the cave proves it functionally effective and environmentally adaptable in harsh underground conditions. In the case study of Dublin Port Tunnel, wireless field measurements of the cross-passage tunnel section show that its deformation is still increasing with time even after more than a decade’s operation. The mode and magnitude of the observed ongoing tunnel deformation are believed to be caused by three effects: twin tunnel interaction effect, cross passage effect and seasonal effect, and the mechanisms behind these observations are deemed to be related to both the surrounding ground and tunnel: ground hydro-geological degradation and tunnel hydro-mechanical deterioration. The seasonal temperature change contributes to the cyclic variation of the elastic and reversible deformation whilst tunnel deteriorations lead to the plastic and irreversible deformation. The field measurements are then compared against the numerical results from a series of soil-fluid coupled three-dimensional finite element analyses where the time-dependent ground and tunnel deteriorations are considered. The three-dimensional finite element (FE) analyses evaluate the individual effect of tunnel hydraulic and mechanical deterioration, ground permeability anisotropy, and ground creep. The numerical rate of tunnel deformation is compared against the field measurements to examine the numerical model. The FE results suggest that limestone rheology is the dominant factor contributing to the ongoing tunnel deformation, despite a slight difference between the deformation modes possibly due to the neglection of localised ground creep in the ground in between the twin tunnels. Parametrically, coupled deterioration leads to greater deformation than that individual deterioration does, and localised deterioration induces more accurate tunnel performance than that uniform deterioration does.
Wireless sensor network, Tunnel long-term performance, Time-dependent deteriorations, Field monitoring, Numerical simulations
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