International Marine & Dredging Consultants NV (IMDC), more, executant
Abstract
The Liefkenshoektunnel is the third road tunnel under the river Scheldt north of Antwerp. The tunnel is 1374 m long, 31,25 m wide and consists of 8 elements built on shore. The tunnel elements were towed to the site where they were immersed in a trench. The dredging works for this trench (28 m below low water) formed the main topic of this morphological study. With a navigation channel of 300 m width and 8,50m depth below low water, the trench caused an enormous perturbation of the hydraulic situation of the river, especially with a tidal range of more than 4,5 m. As a consequence, important siltation processes could be expected. Therefore IMDC was asked to execute the following tasks:
Preparation, coordination and partial execution of an in situ measuring campaign concerning tide, currents, salinity, turbidity and sediment transport;
Reporting and interpretation of the results of the measuring campaign;
Calibration of a two dimensional mathematical model to simulate water flows and sediment transport around the tunnel site;
Simulation of the morphological evolution of the site for different executional schemes of the dredging and immersion works in order to select the optimal working scheme as well as the most appropriate dredging equipment for maintaining the trench depth.
Taking the importance of the simulations in the selection process into account, IMDC was solicited to take full responsibility over the control measurements and the scientific monitoring of the dredging) works during the entire immersion activities of all 8 elements. This monitoring and control programme included regular measurements of bathymetry, in situ sediment density, currents, turbidity, sediment transport, etc. Especially at a critical moment like just before the immersion of an element, this monitoring programme allowed to pass sound judgment on the acceptability of the natural conditions for safe operations.
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