Contracting - Case Study
Heathrow Airport Terminal 5, London
Main contractor Laing O’Rourke used the Dawson Construction Plant, Liebherr LRB255 rig and four-cylinder Push-Pull on a variety of sub-contracts at Heathrow Terminal 5. Shown left is the installation of 160 No Larssen LX32 sheets between 12 & 13m long. They were driven 11m into very stiff London clay (cohesion in excess of 200kN/m2). The temporary sheets were required to form an excavation for the construction of the Southern baggage tunnel. The sheets had to be installed quietly and without vibration because of their close proximity to the main site offices. The alternative use of an impact hammer would have limited working to just the weekends.
The sheets were fully driven within two working weeks without pre-augering or water jetting. Installation accuracy far exceeded “standard” piling tolerances using only a string line.
Shown below is a subcontract to extract and then re-drive 48No x 11m long LX32 sheets, which were forming a retaining wall against an aircraft holding area. These sheets had been installed 12-months earlier, using a percussive piling hammer. Subsequently, sensitive services had been installed and the sheet pile retaining wall had to be re-positioned. It was not permitted to use vibrators for extraction so the four-cylinder Push-Pull was selected (as shown below). Initially, all four-cylinders were used for the extraction but the final part of the process was completed by the two central cylinders. The rig was then able to track with the two sheets and reposition them. Once all the sheets had been threaded into their new position back driving was carried out using all four cylinders. Including the rig operator, two men carried out the entire process.
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