Case Study: ArcelorMittal Sheet Piles Basement, Donegal Quay

ArcelorMittal Sheet Piles Basement, Donegal Quay

Contract No:C533
Client:Lagan Construction
Location:Donegal Quay, Belfast
Value:Approximately £1 million
Summary:Design, supply and installation of sheet pile cofferdam and propping system to facilitate construction of a 2 storey basement for a Hotel, Apartment and Leisure complex adjacent to the river Lagan in central Belfast.

Sheet Piling (UK) Ltd were employed by Lagan Construction who were the Principal Contractor for construction of the basement to the proposed complex. The clutches of the sheet piles were welded after excavation to give a fully watertight sheet pile basement.

The design, with only one level of frame for a 7.5m excavation, required the installation of AZ36-700 ArcelorMittal Sheet Piles 18m long. The ArcelorMittal Sheet Piles were generally supported by twin HZ775 ArcelorMittal walings and 927mm dia tubular props at 7m centres. The Hotel section of the basement was supported by twin 914x305mm walings and 914m dia tubular props.

The ArcelorMittal AZ Sheet Piles were supplied directly to site from a mill rolling in loose double Z piles and in grade S355GP steel.

An initial excavation, to a depth of 3 metres, was carried out and a piling platform installed to allow construction of the CFA piles. The sheet piles acted in cantilever during this stage and were monitored for movement, owing to the presence of the tidal ground water level, and the deep layer of sleech. Old stone dock walls and hundreds of timber piles had to be removed before the concrete piles could be installed.

The soils consisted of approximately 1 metre of made ground overlying 8.5m of soft organic silty clay (known locally as Sleech) overlying 7m of glacial sands over lying glacial clay. The high tide water level was approximately 2 metres below ground level.

The sheet piles were installed using a Bauer RG18T telescopic leader rig and 1000kN vibro hammer. The piles were backdriven to level using a BSP 357 hydraulic drop hammer.

The sheet pile clutches were temporarily sealed with Beltan sealant prior to installation, and were then fully welded during the two stage excavation to give a fully watertight basement.