Tunnel trench under Fehmarn Belt is up to 1.8 metres too deep
The contractor's measurements show that only 1.84 percent of the trench is as it should be, making the trench's condition a central dispute in the Fehmarn construction.
Data shows that the excavation of the tunnel trench is very uneven and not ready for use. Photo: Femern A/S
The client talks about 30 centimetres. The contractor's measurements show up to 1.8 metres. On the seabed off Rødbyhavn, a trench has been dug, which is the entire foundation for the world's longest immersed tunnel. Here, data from the main contractor, Femern Link Contractors, shows that the bottom in many places has been dug far below the planned level: Up to 1.8 metres too deep. Nevertheless, the client, Femern A/S under Sund & Bælt, maintains that the work is progressing as expected and that the deviations are only about 30 centimetres. Thus, two different perceptions of reality stand against each other at the beginning of the most crucial section of the tunnel construction.
An internal report from the main contractor, Femern Link Contractors, shows that the tunnel trench has large holes and is far from meeting the requirements to be the foundation for the 89 tunnel elements that will connect Denmark and Germany. The measurements cover the first 650 metres off the coast of Lolland and show that only 1.84 percent of the bottom meets the technical requirements that must be fulfilled before the first tunnel elements can be lowered.
Purple indicates the worst affected areas. Red/orange is too deep in one reference. Green is within requirements.
Dug up to 1.8 metres too deep
Data shows that the bottom on average lies between 51 and 86 centimetres below the level it should have. In some places, it has been dug up to 1.8 metres too deep. This means that the vast majority of the excavation, which is to form the foundation for the tunnel elements, does not lie within the tolerances that the project is working with.
According to the report, almost the entire trench is more than 30 centimetres below both the planned design level and the reference level used as control. Only 1.84 percent of the area meets the requirements, while the rest is too low.
The zones TE-77, TE-78 and TE-79
The survey covers three so-called sub-zones, which together form the first part of the tunnel trench. The zones are called TE-77, TE-78 and TE-79 and are in continuation of each other towards Germany and are to accommodate their respective tunnel elements.
Each zone has its own measurement grid and functions as sections in a chain sequence that stretches all the way through the Fehmarn Belt. In these sections, the first tunnel elements will be placed when the immersion begins. In TE-77, the bottom is on average 75 centimetres below the design level. In TE-78, the difference is 86 centimetres. And in TE-79, the bottom is 51 centimetres below.
In a press release from 17 September, Sund & Bælt stated that parts of the trench were about 30 centimetres deeper than planned, but that it could be managed by laying a thicker layer of gravel under the tunnel elements. According to the developer, the process is therefore as expected, just with a need for greater adjustment than initially assumed.
If the measurements from the first 650 metres of the tunnel trench are representative of the rest of the trench, the problem is much larger than the picture the client has publicly presented. Deviations of this magnitude typically require extensive rectification work before the trench can be used as a foundation. And additional costs will amount to around 750 million kroner.
The current situation is that Femern Link Contractors will not approve the tunnel trench in its current form. This means in practice that the contractor will not proceed with the work until there is agreement on the condition of the trench and the requirements for it are met.
One of many conflicts
The disagreement over the condition of the tunnel trench is just one of the conflicts on the large construction project. Femern Link Contractors has made a claim of 1.95 billion euros, equivalent to 14.5 billion kroner, due to changed conditions and thus delays. At the same time, there is an ongoing international arbitration where FLC has made a claim of 77 million euros in connection with delays and additional costs during the coronavirus pandemic.
FemernBusiness has presented the measurements to Femern A/S. The client does not wish to comment on the specific data and refers to the discussion about the quality of the tunnel trench as part of contractual negotiations with FLC.
Femern A/S instead points out that the biggest challenge for the schedule is the completion and approval of the special vessel for the submersion of the tunnel elements, which is now over a year and a half delayed. At the same time, the developer assesses that a first submersion in 2025 is not realistic, but that it will happen as soon as possible once the vessel is approved.
