Monitoring the Structural Response of the Liefkenshoek Rail Tunnel to Tidal Level Fluctuations

Abstract

The 6-km-long Liefkenshoek rail tunnel creates a new freight connection in the Port of Antwerp (Belgium) by crossing the River Scheldt and Port Canal. The water level variation of the river, corresponding to the tides of the North Sea, proved to be a nonnegligible load state for the tunnel lining. This paper reports how the structural response of the Liefkenshoek tunnel to the tidal fluctuations could be identified, thanks to the various components of the complementary monitoring program, consisting of strain, ovalization, and leveling measurements. First, an in-depth study on the methodology of the applied monitoring procedures is presented. Next, results show that the tidal effect causes an oscillating vertical displacement of the tunnel lining up to 10 mm between low and high tide. Outside the river boundaries, no significant tidal influence is found, and the transition zone between the stable tunnel section and the moving part below the river appears to be constrained to a relatively small tunnel section. Furthermore, the concrete lining shows a uniform compression and relaxation between tides. The corresponding monitored stress changes show a good resemblance with results from simplified analytical calculation. The findings of this paper perfectly illustrate how the design process of segmental tunnel linings requires a thorough understanding of the project surroundings for a correct identification of all loads on the precast concrete elements, both during and after tunnel drive works.