Ground conditions are complex but familiar
The result of the investigations is largely in keeping with previous feasibility studies from 1995 and 1996 which were commissioned by the Danish and German Ministries of Transport. The recent findings, however, reveal the Palaeogene clay layer near the coastal areas to be more affected by the glaciers of the Ice Age than previously assumed.
The Palaeogene clay layer off the Danish coast lies so deep that it will be unaffected by the construction work. Off the German coast, however, dredging has to be carried out in the Palaeogene layer because the layer is very close to the seabed.
Large scale testing
In order to obtain more geotechnical information and practical experience of working in the Palaeogene clay layer, Femern A/S has established a specific test field approx. 1 km off the German coast at Puttgarden. Until 2013, large scale testings aimed at measuring and monitoring movements in the soil under different impact conditions will be carried out.
The aim is to measure the soil’s properties and assess how supporting construction components are affected by natural forces.
The results from the test area will provide important information on key issues such as settlements and upheavals of the soil as well as bearing capacity for piles and ground anchors.
The piling tests are also part of a research and development project which examines how the bearing capacity of piles is affected over time. Femern A/S is a participant in the project which is headed by Norwegian Geotechnical Institute.
Graphic presentation of selected large scale tests in the area off the German coast
Geotechnical borings
During 2009 and 2010, Femern A/S carried out around 100 borings on land and at sea in a 2 km wide corridor east of the ferry ports in Rødbyhavn and Puttgarden. The drilling depth was 50-100 m into the soil or the seabed.
The purpose of these borings was to collect high quality soil samples and to measure the strength and other important conditions in the soil by using the so-called Cone Penetration Testing method.
In order to make use of past experience, Femern A/S has carried out equivalent borings at the older of the two Lillebælt bridges and at the Fehmarnsund Bridge in Germany. Both bridges are founded on the same type of soil stratum as is found in the Fehmarnbelt. Ever since the two bridges opened to traffic in 1935 and 1963, ongoing measurements have been undertaken.
The boring works were undertaken for Femern A/S by the Dutch company Fugro Engineers BV.
Laboratory testing
Selected portions of the collected soil samples from the borings in Fehmarnbelt were examined at special laboratories in order to determine the deformation and strength properties of the soil. Around 2.500 samples corresponding to approx. 25 tonnes of soil have been examined.
Advanced tests at the laboratories have returned the soil samples back to the natural load situation from where they were taken before being exposed to the simulated effects of construction.
The advanced laboratory tests were carried out by GEO on behalf of Femern A/S.
Geophysical measurements
To obtain a clearer understanding of the nature of the soil and seabed, Femern A/S has also carried out a number of geophysical surveys.
In 2009, a vessel carried out seismic investigations in an extensive area of Fehmarnbelt using special equipment. The measurements were taken at intervals of only 25m close to the Rødbyhavn – Puttgarden ferry route.
Unique positioning system
As part of the geotechnical programme, Femern A/S has, in conjunction with German and Danish geodetic authorities, established a special satellite positioning system for the Fehmarnbelt project.
Two reference stations on each side of the Fehmarnbelt can receive, adjust and forward position signals from the American GPS, the Russian Glonass and the European Galileo systems. This provides secure and accurate locations and will make it possible to plan and build the Fehmarnbelt fixed link with a very high degree of accuracy, i.e. within a tolerance of a few millimetres.
