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Limerick tunnel gets going with initial piling and temporary works

DEW PILING is due to complete piling and temporary works on the new 2400M (£269M) Limerick Tunnel this month. The contractor will deliver part of the piling element for the 900m immersed tunnel - running beneath the River Shannon in the Republic of Ireland - as part of a public private partnership scheme for the National Roads Authority.

Dew is installing the temporary works for tunnel portal entrances.

The temporary access stagings consist of 23m long, 820mm diameter tubular piles, cross beams and longitudinal beams, which will be decked out in crane mats.

The subcontractor is also building a combi-wall using 1.4m diameter tubular piles and sheet pile inlls followed by a reinforced capping beam. This will provide a route out to the tunnel works within the river once the tunnel segments have been completed in the casting basin.

Due to the geological prole at the site, which consists of soft alluvial soils overlying hard limestone, the piling company is also pinning the base of the tubular piles with 4m long steel dowels. These are 508mm diameter tubes grouted into 600mm diameter rock sockets drilled into competent limestone.

A channel is currently being dredged in which the tunnel will be submerged in four segments at a depth of about 10m beneath the riverbed. The design incorporates two tunnels, each with dual carriageways and features emergency walkways on either side for safety.

Work on the south side is well advanced, with all of the 134 tubular piles now installed in the combiwall. Site workers are now drilling piles to x the combi-wall in place and provide a structure within which water levels can be controlled. Dew expected to complete this work early this month, enabling the construction team to cast the south side concrete tunnel portal.

Meanwhile, the subcontractor has started work on the north side of the tunnel, where it is installing a similar number of piles to build another combi-wall. This will take around 15 weeks to complete.

Dew is working in joint venture with sister company Lagan Construction on the £10M temporary foundations and construction package. The main contractor is DirectRoute (Limerick) Construction, a consortium comprising Strabag AG, John Sisk & Son (Holdings), Lagan Holdings and Roadbridge.

The project includes 10km of new dual carriageway, ve river crossings, two toll plazas and connecting roads. When complete, the tunnel will link all national routes converging on Limerick from Dublin, Tipperary, Cork, Kerry, Waterford, Ennis and Shannon Airport.

Work on the new tunnel began in late October 2006 and will take four years to complete. Once operational, it will divert an estimated 40,000 vehicles per day from the centre of Limerick.

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