Leading tunnelling and ground engineering contractor
behind the UK's most prestigious underground projects

Skanska's underground construction, refurbishment and geotechnical projects include the largest, most complex and prestigious schemes in the United Kingdom, whether it be for rail, road or utilities. In keeping with its leading position Skanska UK holds safety, quality control and environmental considerations as top priorities. The Company is accredited under OHSAS 18001 for its safety management system, accredited to ISO 9001 for its quality management systems, and has ISO 14001 accreditation as part of its drive for consistently high environmental performance.

Handling complexity
The increasing complexity of today's underground construction projects can present challenges in terms of multi-faceted tasks, innovative techniques and novel designs. Skanska approach all projects confidently with a combination of proven traditional methods and the very latest technology in materials, equipment and methods. These include hard-rock and soft-ground tunnelling with closed and open faces, feasibility studies, ground stabilisation techniques, sprayed concrete lining design and application, ground imaging, geotechnical monitoring, and mechanical and electrical installations.

Successful major tunnelling projects include the Channel Tunnel Rail Link (CTRL), now under construction, in which Skanska is a leading participant in four major contracts totalling over £500 million in value. All involved innovative solutions and true teamwork in integration with the Client and consulting engineers as well as other joint-venture contracting partners. Major features of the project included:

• The Stratford International Station 'box' - a 1071m-long, 24m-deep concrete structure below the surface in east London;
  
• Twin 7.5-km-long tunnels to connect Stratford Station with the St. Pancras terminal in north central London, passing under heavily built-up east London;
  
• Twin 4.5-km-long tunnels connecting to the east of Stratford Station;
  
• A series of cut-and-cover tunnels through the Kentish town of Ashford in phase 1 of the CTRL, involving complex rail alignments and interactions with existing structures.

The project won the British Construction Industry Award (BCIA) Major Project Award. Earlier Skanska was also part of the joint venture redeveloping the original Stratford Station for London Underground. The underground works here consisted of jacking a 7.7m x 4.35m section concrete box structure over 54m under three sets of live railway routes during track possession periods.

Since 1985 Skanska has been part of the consortium that completed over 35 km of tunnels for the Greater Cairo Wastewater Project, Egypt, in a contract valued at £394 million. Tunnels in diameters from 1.20m to 5.00m, and 132 shafts of 4.85-5.00m i.d. and depths to 30m were constructed using earth-pressure-balance, mixed and slurry-shield tbms, compressed air working, and specialist sewer lining, all integrated with the local workforce.

Back in London, work has been progressing in preparation for the planned cross-city Crossrail project. Skanska was responsible for constructing an 8.2-m diameter, 40m-deep draught-relief shaft below the 10m-deep basement of the Moorhouse development in the City. Work included dewatering the basal Thanet Sands with 17 wells, constructing the shaft with concrete segment lining, and monitoring for associated ground movements. The Moorhouse structure is designed to accommodate the shaft, future tunnels and associated railway structures.

Tunnels at various depths under Wimbledon, in south-west London, which carry high-tension electrical power cables for National Grid, were recently refurbished over a total length of 3.2 km. Typical work includes the installation of cable-cooling and fire-suppression systems.

Reconstruction of the Horsfall Tunnel, on the Manchester to Normanton rail route was carried out in a £1.4 million contract for Railtrack. This required the complete rebuilding of a 30-m portal section, plus the renovation of the rest of the 250-m long tunnel lining within a 4-week rail-line possession. The work included retaining the hillside behind a 14m-high reticulated minipile wall (300 No. x 220mm-diameter to 16m depth), reinforced concrete construction, and trackwork. The project won the Yorkshire ICE Merit Award.

In the water sector Skanska recently conducted repairs to the Ffestiniog hydropower station shaft in north Wales, and upgraded a fish-pass tunnel through hard rock at Conwy Falls, also in north Wales.

For the Dartford Crossing road tunnels, to the east of London, which are a vital link in London's M25 orbital motorway route, Skanska was responsible for the replacement of deteriorated highway decking and tunnel lining cladding panels in the two bores in turn.

Multi-disciplined
Other recent projects include:

• A £2.4-million joint venture sub-contract on London's Jubilee Line Extension for compensation grouting and monitoring to protect existing structures from possible movements due to tunnelling. Design and analysis of the compensation grouting used a 3-dimensional model of the works and overlying structures. This allowed all records and progress monitoring to be shared with the main contractor and client electronically.

• Lift shaft, access tunnel and basement works for Harrods store redevelopment. Geotechnical aspects of the work were valued at £8 million, and included compensation grouting, with high accuracy monitoring, to avoid building settlement. It received the Construction Industry IT Award, the Deep Foundations Institute International Outstanding Project Award, and the Quality in Construction Award for Specialist Contractor of the Year.

• Various hydropower projects, cable tunnels, mine roadways and shafts, large sub-surface excavations, retaining walls, slope stabilisation, piling, dewatering, underground cavity detection, mapping & rectification

• Three-dimensional seismic tomography (3D Tomographics) used for identification of geological structures ahead of tunnel faces and in mines, mapping of underground cavities for potential instability and rectification required, and surveying of piles and foundation structures where drawings are not available.

For more information on these and many other Skanska tunnelling projects, or our vast range of tunnelling and underground refurbishment and ground engineering techniques, contact:
Skanska UK Civil Engineering, Tunnelling Division, Bentley House, Jossey Lane, Doncaster, South Yorkshire DN5 9ED, UK.
Tel.: +44 (0)1302 821100; fax: +44 (0)1302 821105; e-mail tunnelling.division@skanska.co.uk or visit www.skanska.co.uk

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