The Fehmern Baelt Fixed Link - The longest tunnel trench in the world will be asking for new dredging tools
Type:
Presented during:
CEDA Dredging Days 2009 - Dredging Tools for the Future, Rotterdam
Authors:
Steen Lykke, Project Director, Tunnel; Claus Iversen, Project Manager, Marine Works, Tunnel; and Stephen Pearson, Lead Engineer, Marine Works, Tunnel
Abstract: Following the signing of a Treaty between Denmark and Germany in September 2008, the Fehmern Baelt Fixed Link, connecting Scandinavia (Denmark) with the European Continent (Germany), finally got off the ground and has since then started moving into the initial Conceptual Design phase. This phase is the first step of a 10 year design and build process.
The fixed link will carry four lanes for road traffic as well as two tracks for railway traffic. A cable stayed bridge is the preferred solution and an immersed tunnel is the preferred alternative. An immersed tunnel will by far be the longest and the biggest immersed tunnel ever constructed. Conceptual design of both solutions is now being prepared as parallel activities.
The Fehmern Baelt Strait is approximately 19 km wide and the water depth varies between 20 and 30 meters within the heavily trafficked navigational channel, which covers approximately 50% of the total width. The expected construction period for both solutions is 7 years - with approximately 5 years allocated for the dredging and reclamation works - which in itself calls for a number of new innovative construction solutions. Obviously the two alternative schemes involve some comprehensive but also rather complex marine operations and construction works - starting with dredging of the 19 km long and 11 - 14 meter deep tunnel trench - or alternatively with a series of up to 15 m deep pits for the foundation of bridge piers. Dredging and reclamation volumes vary between 20 million m3 for a tunnel trench and approximately 4 million m3 for a bridge solution. The maximum dredging depths will for both solutions be in the order of 45 m.
The paper will give a general description of the two alternative solutions - bridge or immersed tunnel - but will focus on major challenges for the dredging works in terms of dredging depths, expected techniques and capacities needed to meet the tight construction schedule. The works must be executed under strict environmental control in soil conditions varying from soft soil to hard formations of clay till in the northern section of the Strait. As much as possible of the dredged materials can be expected to be transformed into engineered fill in purpose build reclamation basins.
Also the need for import of up to 15 million m3 of quality fill for backfilling of the tunnel trench and/or reclamation of anchor block islands for the bridge will be addressed.