Case Study: Stublach Underground Gas Storage Temporary Sheet Pile Cofferdam

Stublach Underground Gas Storage Temporary Sheet Pile Cofferdam

Contract No:C841
Location:Northwich, Cheshire
Value:Approximately £912,000.00
Summary:Design and construction of a lime stabilised sheet piling platform capped with 6F2 material. Supply and erection of site perimeter fencing and gates. Sheet piling design, sheet pile supply, sheet pile installation and extraction of steel sheet piles to form a temporary earth retaining structure. The trench cofferdam facilitated the excavation and construction of the proposed Gas Compressor Station. The retaining structure consisted of 1066 lin.m (1546 no. piles). In addition a further 134nr 11 to 12m long piles were supplied and installed to form a rectangular four sided cofferdam to facilitate construction of a new methanol tank.

Sheet Piling UK Ltd were employed to complete the sheet pile design and construction of a temporary steel sheet pile trench cofferdam consisting 1066 Linear Metres of sheet piles ranging from 5.0 to 12.0m long. The trench piling is to facilitate the construction of a gas compressor station and excavation up to 4.5m in depth.

During the initial period on site Sheet Piling UK were employed to establish suitable office and welfare facilities, Erect perimeter site closure fencing and gates and to design and construct a suitable piling platform in accordance with BRE Digest 470 ‘Working Platforms for Tracked Plant’. After considering various options the platform was constructed using lime/cement stabilisation (see above) and capped with 6F2 imported aggregate.

The 1680 no. steel sheet piles of various sections were installed using ABI and Bauer Telescopic Leader Rigs mounted with a high frequency vibratory hammers all serviced by a crawler crane. At peak 3nr gangs were employed for the pile installation in addition to a full time attendant gang.

The general soil profile consisted of firm clay over loose to dense Sands and Gravels over weathered Mudstone. As a safety initiative all deliveries were pre-slung in order to control the hazards involved in unloading/loading operations. The sheet piling installation was completed ahead of programme, within budget and without incident. Sheet pile extraction is programmed for December 2011.