TRANSPORT | IMMERSED TUBE TUNNELS


demolition of the bulkhead walls and the concreting of the coupling joint. Once the tunnel element has been underfilled and bedded, the permanent ballast in the form of the road substructure is installed inside and gradually replaces the ballast water. Finally, the ballast tanks are removed. After lowering the tunnel elements and constructing


the final joint between the last element and the C&C tunnel on the north side, the water-side shoring is dismantled to restore the original shoreline.


6.5 Preparatory work for the immersed tunnel The sheet piling for the bank protection walls on both sides of the river was installed from the summer of 2025 to April 2026. The preliminary excavation, including the installation of horizontal anchors to support the river sheet pile wall in the contaminated area to the north, was completed at the end of April 2026. This was followed by the installation of ground anchors as support for the immersion channel sheet pile wall. The same sequence of works is repeated on the south bank. In the southern section of the immersed channel, a


Above: Figure 10. Preparatory work in the dry dock for the construction of the next two concrete elements. Credit: Eric Shambroom Photography


previous element at the primary end using a pin-grabber construction and is supported at the secondary end by pins and hydraulic presses on the previously placed temporary foundations. A compression system is then used to lightly press the GINA profile against the previous tunnel element in order to drain the coupling joint (the space between the two tunnel elements). The water pressure pushes the two tunnel elements firmly together, further compressing the GINA profile (see Fig. 9). To ensure the required bedding, the elements are


Below: Figure 11. Drawing showing the cross-section of the deepest immersed element in the Weser river, once covered, after


completion of construction. Credit: Wayss & Freytag


underfilled with a water-sand mixture. Once the filling process is complete, the position of the element is secured horizontally by filling at the sides. The pins are retracted from the temporary foundations and the prestressing cables are cut. To backfill and cover the elements, sandy soil is transported from the Outer Weser to the construction site by barge, restoring the riverbed to its former state. Coarse stones are placed above the tunnel, as protection against anchors or ship impact, before the final level is filled in (Fig. 11). A so-called omega seal is installed in the coupling


joint between the previously lowered and the new tunnel element. Together with the GINA seal, two sealing levels are thus provided. This is followed by the


solid bulkhead had to be built between the river and land side immersion channel to substitute the interrupted dike line of the southern bank. The 1.5m-thick slurry walls installed for the excavation of the immersion channel will be reinforced by a jet-grouted grid at a depth of approximately 25m. The tunnel elements No 5 and No 4 will later be placed on top of this jet-grouted grid. This preparatory work will continue until late summer 2026. This will be followed by wet excavation of the channel.


7 - CONCLUSION The Weser crossing is a particularly unusual construction project, mainly because it is being built as an immersed tube tunnel. Other challenges include the excavation pits, which are up to 30m deep, the immersion of the elements during ongoing shipping traffic and the tidal range of more than 4m with the corresponding current speeds in the river. For the client, DEGES, this method of tunnel


construction has two main advantages: firstly, it is the more economical option compared to a bored tunnel; and, secondly, the concrete elements can be prefabricated in parallel, nearby in Bremerhaven, away from the main construction site. This reduces the construction time considerably.


16 | July 2026


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45