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Deep data on Fehmarn Link May 2011
Patrick Reynolds, Freelance Reporter
The geotechnical investigation report for the Fehmarn Belt immersed tube tunnel between Denmark and Germany has been released, and Patrick Reynolds reports that while studies continue into glacial clays the client believes the data should be useful for contractors keen on early insight into the construction challenges of the scheme before the prequalification call is issued next year.
Contractors interested in possibly bidding for the world's longest immersed tube tunnel across the Fehmarn Belt between Denmark and Germany will be able to study geotechnical data collected to date following the client's release of the information this week. Although the bidding procedure is not yet determined, invitations to prequalify for the 21km long road and rail tunnel could be issued in less than a year. The client, Femern A/S, expects the procurement phase to run over 2012-13 to enable construction to commence in 2014.
Site investigation report of the strait seabed released

Site investigation report of the strait seabed released

About 15.5 million m3 of dredging is needed to form the trench at up to 43m below sea level. A planned 89 elements of 217m long x 8.9m high x 42.2m wide and weigh 73,500 tonnes would carry the road and rail link across the strait with10 special elements placed at 1.8km intervals.
On releasing the information, Femern A/S Geotechnical Manager, Jens Kammer, said, "there are no geological or geotechnical obstacles to constructing a fixed link in the area”. Some additional studies are continuing however, close to the German coast where 'fat' clays need further analysis to inform the tunnel design and dredging operations. Contractor Fugro undertook the programme of borings across the 19km-wide Fehmarn Belt. Drilling started two years ago at 50 test locations with two bores of up to 100m deep at each site. JV Ramboll-Arup also did geophysical tests offshore. The extra work is being executed by Per Aarsleff.
Geology along the alignment comprises moraine clay, chalk and a complex plastic, or 'fat', clay – the Palaeogene type – which has required further study. The moraine and 'fat' clay beds were found to be more glacially disturbed than expected. Given their greater construction challenge, a large 30m x 60m test area has been set up 1km off the German coast to gain more data and experience working with the 'fat' clay deposits.
The Ground Investigation Report released states that the Palaeogene deposits tested near the fixed link corridor are all high plasticity clays. The clay content is typically 70%-80% with typical plasticity index of 50%-140%. There are also fissures related to slicken sides.
  • Road and rail immersed tube design

    Road and rail immersed tube design

  • 'Fat' clays present a particular challenge

    'Fat' clays present a particular challenge

"There is enough data for interested contractors to start studying the construction challenge," said Kammer, "so that they are well prepared for when the construction work is put out to tender."
Earlier this year Danish politicians fell behind the tunnel option for the €5.1 billion (about US$7.25 billion) fixed link. Focus now moves to preparing the environmental impact studies and obtaining planning approvals. Regulations require that the alternative cable stayed bridge option also be included.
Femern A/S has been supported in development of immersed tube tunnel concept by a consortium of Ramboll Danmark, Arup and Tunnel Engineering Consultant. Their subconsultants are WTM Engineers, HTG Ingenierburo fur Bauwesen, Oriental Consultants, Schonherr Landskab and Wilkinson Eyre Architects.
References
Immersed tube recommended for Femern link - TunnelTalk, Nov 2010
Political backing to Denmark-Germany link - TunnelTalk, Feb 2011
Cost comparison for Femarnbelt link options - TunnelTalk, Nov 2010

           

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