Structural and structural engineering for the repair of the sheet pile walls of the Eider barrage in the sluice area

The further progression of corrosion and the increase in cover material damage due to material erosion of the backfill require the repair of the sluice-side sheet pile walls at the Eider barrage to ensure long-term traffic safety and the stability of the dividing mole and guide dam. The measure must be coordinated with the boundary conditions of the Eider barrage. The bottom of the sluice area is reinforced due to the prevailing high flow velocities of up to 5m/s. In the area of the openings, the bottom protection is provided by a reinforced concrete slab. With a total length of 150m, this is bordered by a rigid bottom protection made of granite blocks weighing at least 0.4 to 0.6 t. These were laid on a multi-layer filter and have a height difference of up to 15cm between them. The bottom protection is completed by weighted sinkers. The length of the sluice-side sheet pile walls is approximately 735m in total. As part of the repair of the sheet pile walls, the cover material on the dividing mole and guide dam must also be renewed. There are already large-scale under-excavations in this area. During the repair of the cover material of the dividing mole, existing plans for the renewal of lighting and electrical cables must be integrated. In the spring of 2024, the sheet pile wall anchors were exposed at several points to check their condition. Both the visual inspection and the residual thickness measurement showed a good condition of the round steel anchors without significant cross-sectional loss, so that their load-bearing capacity can be included in the planning process. When planning the repair of the sluice-side sheet pile walls, it is particularly important to consider the boundary conditions of environmental influences, barrage operation and nature conservation. The location at the Eider barrage is particularly exposed to the weather. High humidity, precipitation and strong winds occur throughout the year. The seaward areas of the dividing mole and guide dam are not protected by the barrage and can be completely flooded during storm surges. Between September 15th and March 31st, double dike safety must be ensured at the barrage. Both closure rows of the barrage must be operational at this time. Work on the dike foot is prohibited during this period. From April to September, areas of the barrage site are populated by seabirds. Some species, such as the common tern, are endangered, so close coordination with nature conservation will take place during the repair of the sheet pile walls. The operation of the barrage affects many affected parties. This must be taken into account if the measure requires adjustments to the barrage operation. Due to the diverse interests, it may also be necessary to make short-term changes to the barrage operation. During the storm surge-free period in the coming years, the sluice closures of the barrage will be repaired. The barrage will be operated in n-1 mode. One sluice opening will be closed, the opposite gate will be moved to the high position and enclosed for corrosion protection work. The reduction of the flow cross-section by closing an opening results in higher flow velocities in the rest of the sluice area. Work in the sluice area on or under the water is only possible if a flow-free state is established (i.e., all sluice gates are closed). Otherwise, the sluice area is a restricted area. The flow-free state cannot be maintained for longer than the duration of a tide, among other reasons due to the ecological influences of a decreasing salt content on the inland side of the barrage.