With a length of 17.6 km and foundation depths reaching more than 40m under the sea surface, the Fehmarnbelt Fixed Link between Fehmarn in Germany and Lolland in Denmark will be the longest combined rail and road tunnel to date. Built using immersed tunnel technology, the link will carry a four-lane motorway alongside a twin-track electrified railway. The Fehmarnbelt Fixed Link will consist of individual reinforced concrete tunnel elements that will be manufactured in a plant and will be specifically constructed for this purpose in Rødbyhavn on the Danish Coast.
The construction of the immersed tunnel is divided into two parts of equal size: one for the northern section of the tunnel and another for the southern section. Both sections will typically comprise of standard tunnel elements, with special elements at fixed intervals along the tunnel length.
The entrance tunnel elements of the Fehmarnbelt Fixed Link will be exposed to severe coastal/seawater conditions and freezing temperatures. The combination of these severe environmental conditions and the 120-year design-life requirement call for highly durable concrete.
SIMCO was hired by the Salini-Impregilo/Samsung/Bunte Joint Venture (SISBU-JV) to provide an independent assessment of the durability of the precast reinforced concrete elements of the Fehmarnbelt Fixed Link project.
SIMCO’s scope of work in this project was to conduct a preliminary analysis focused on the durability of four (4) candidate concrete mixtures designed by SISBU-JV. All candidate mixtures were designed to be durable when exposed for 120 years to the very harsh environmental conditions, where reinforced concrete elements are expected to be in contact with seawater throughout their service life. The analysis was based on a review of documents provided and on a series of numerical simulations supported by a laboratory program aimed at providing transport properties for long-term prediction.
A comprehensive testing program was also initiated to further document the long-term physical properties and durability of the selected mixtures. Part of this program was conducted at the laboratory of Aalborg Portland in Denmark. Additional tests were performed in SIMCO’s laboratory in Canada.
The numerical simulations performed were to evaluate the resistance of concrete to chemical damage and chloride-induced steel corrosion over the specified 120-year design life. Simulations were performed on critical structural elements, each having its own set of exposure conditions established on the basis of a detailed analysis of the actual environmental conditions of the project.
All concrete durability calculations were run using a testing protocol specified by the U.S. Department of Defense for the design and construction of marine concrete structures.