IMMERSED TUBE TUNNELS | TRANSPORT
● Construction of the operations buildings on the north and south sides
● Road construction along the entire length ● Landscaping.
The logistical challenge arises from the production
of the concrete elements in Bremerhaven, the towing process to Bremen for temporary storage and the actual lowering into the Weser. Added to this are particular characteristics such as the tidal range of the Weser of approximately 4m in Bremen, the changing flow directions and speeds, shipping traffic, dredging work for the trench in the Weser and the up to 20m-deep excavation pits with existing contamination in the form of slag deposits from the neighbouring steelworks. Another challenge is the impermeability of the final structure, which is exposed to a pressure of more than 25m from the water column. The overall project is divided into four sub-projects:
● North: all construction activities north of the immersed tunnel
● South: all construction activities south of the immersed tunnel
● Bremerhaven: Construction of the tunnel elements in the dry dock
● Weser: transport, floating and lowering of the tunnel elements in the Weser. With a tidal range of 4m and ongoing shipping traffic, the trench for the tunnel is dredged and the elements are lowered into position, one after the other.
2 - GROUND CONDITIONS The entire project section is located in the marshland of the Weser lowlands. Underneath the topsoil there are various fill materials, mainly characterised by the industrial use of the land on the north side of the river. The fills consist of relocated cohesive soils and sands containing various foreign components (including construction waste and slag). The steelworks site contains several metres of iron smelter slag (mainly blast furnace slag), which is considerably consolidated. Beneath the fill material are several metres of slightly
consolidated silty, clayey and organic soil types such as Weser marsh soils consisting of alluvial loam and, in places, peat; there are no marsh soils on the banks of the Weser or in the Weser itself. The marsh soils are underlain by Holocene sands and Pleistocene fluvial sands of the Weser low terrace from the Weichselian and Saale glacial periods, which are widespread. With increasing depth, the sands become coarser and
contain gravel as well as stones and boulders. Below are basin deposits of the Lauenburg layers from the Elster glaciation, mainly in the form of fine sands.
3 - SPOIL: UTILISATION CONCEPT DEGES has drawn up a disposal and utilisation concept for all soils to be excavated and installed in the project. Accordingly, the excavated soil and fill material will be reused as building materials in earthworks and road construction, and for backfilling excavation pits. This does not apply to soil extracted or deposited in the Weser
river during dredging work. Dredged material would be deposited in dumping sites in the Outer Weser or extracted from sand extraction sites in the Outer Weser.
4 - DEEP EXCAVATION PITS - NORTH AND SOUTH
4.1 Excavation pit north of the Weser The northern project area is home to an Arcelor Mittal Bremen steelworks with a slag tip and track fields, as well as a Holcim cement plant (Fig. 3). Industrial use has resulted in fills and large-scale terrain elevations. The route of the road runs through the steelworks site with intersecting and ongoing truck and rail traffic. As steel is produced in shifts 24/7, uninterrupted factory traffic on the roads and railway tracks must be guaranteed. In addition, there are utility relocations for both the
factory‘s own supply and disposal systems and public utilities. Due to industrial pollution, large parts of the soil and groundwater in the area of the excavation pits are contaminated. The extracted groundwater and drainage water is cleaned and then disposed in a controlled manner in water treatment plants. The construction site is also inspected for unexploded ordnance in advance and during construction. Everything above and below the water in the Weser and adjacent areas is examined for possible bombs from the Second World War. The excavation pit is divided into four watertight
sections (North 1 (N1) to North 4, or N4), which connect to the trench in the north and cross both a track field and the steelworks service roads. The difference in elevation between the lowest (N4) and highest excavation pit base (N1) is approximately 12m. The individual excavation pit sections are separated
from each other by watertight bulkheads. Excavation pits N4 (Fig. 4) and N2 will be constructed first so that the tunnel can be built, backfilled and covered as early as possible using the C&C construction method, thereby minimising disruption to traffic for the steelworks. This will ensure that the connection to the immersed tube
July 2026 | 11
Above: Figure 3. View of the northern construction site and the steelworks industrial site.
Credit: Wayss & Freytag Slag protection Site Office
Excavation pit N3 Excavation pit N4
Desanding plant.
Trench Flood protection
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