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8th October 2009
SP.UK Take To The 'AER'!
Sheet Piling (UK) Ltd have recently completed the design, supply and installation of sheet piles to form a permanent underground Aeration Tank at Chelmsford STW. The works were carried out for Principal Contractor Skanska Aker Solutions on behalf of their client, Anglian Water.
The 55.0m x 15.0m x 3.6m deep tank was originally designed as a conventional reinforced concrete structure requiring sheet piles as temporary earthworks support only. However, SP.UK provided an innovative and alternative permanent sheet pile wall scheme including welded interlocks to give an equivalent of a Grade 2 to 4 structure to BS8102:1990 ie. 100% watertight. This alternative sheet piled tank offered both cost and programme savings. Although this has always been a priority, additional focus on cost has recently been required following OFWAT's recent ruling that Water Company's charges are to be capped. Therefore, all future capital works are now being scrutinised and further savings demanded. SP.UK work closely with clients to ensure the most cost effective and innovative solutions are proposed. Anglian Water requested evidence of previous similar schemes and SP.UK provided details of two such schemes where sheet piles had previously been used as permanent water storage tanks.
The 236 no. NSP.3W x 11.00m long sheet piles were installed using a Bauer Telescopic Leader Rig mounted with a 100te High Frequency Vibrohammer, serviced by a 35te capacity crane. Although 'back-driving' with an impact hammer to gain the required penetration into the dense Gravels and stiff Clays was envisaged, the efficient and powerful vibrohammer proved to be more than capable by itself!
As previously noted, the tank was made watertight using a horizontal steel 'puddle flange' water bar and hydrophilic strip at the mid slab height in conjunction with plated and welded pile interlocks from the base soffit level to the pile head level within the RC capping beam. Due to the client's stringent welding criteria and testing requirements, SP.UK had to produce specific welding procedures which are Lloyd's accredited in order to carry out the works. Welder qualifications, acceptance criteria and testing regimes were also formulated.
The 60 year design life was achieved using sacrificial steel thickness to mitigate the calculated corrosion rates of 0.044mm/yr and 0.012mm/yr for the water and soil faces respectively.
In conclusion, cost and programme savings can be gained by utilising steel sheet piles for permanent underground tanks such as Storm Water Overflows, Aeration Tanks etc.
SP.UK can provide a full design and installation service, and can liaise closely with the client's technical consultant to provide the most cost effective and value engineered solutions.
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Contact
Sheet Piling (UK) Ltd.
John Hull (Managing Director) - 01772 794141
NOTES TO EDITORS
Sheet Piling (UK) Limited is one of the UK's leading piling contractors. Owning and operating a comprehensive range of specialist piling equipment Sheet Piling (UK) Ltd also carry extensive stocks of new and used piles enabling rapid reaction to any urgent requirements or emergency situations.
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