Long and detailed planning paid off on an intricate project to squeeze a four-storey building on to a 100m long by 10m wide site next to the Royal Festival Hall (RFH) on London's South Bank.
Housing RFH offi ces, storage space and retail outlets, the new steel frame building will be tucked between the hall and Hungerford Bridge, which carries trains across the Thames and into Charing Cross Station.
Main contractor Taylor Woodrow, working on the project on behalf of the South Bank Board, realised it should involve a piling contractor at a very early stage to cater for pile design and planning constraints. So in October 2003 it turned to its supply chain partner May Gurney Geotechnical.
The key issue for the entire process was the railway viaduct leading to the Hungerford Bridge, running along the western edge of the site.
May Gurney immediately involved Network Rail to determine the most appropriate plant and equipment for the job. This would dictate rig type and in turn the dia meter, length and configuration of the piles needed to provide the required foundation capacity.
May Gurney proposed using its Llamada P140TT rig. Network Rail approved this because, once modifi ed and using its telescopic mast capability, it could be set to the 22.4m maximum height at which it was permitted to work alongside the 9m high viaduct.
But Christmas, a busy time for the Royal Festival Hall, was fast approaching and concerns about its carol concerts meant crews had an additional factor to plan around. In the end they could only assemble the rig on one day, 22 December, without affecting the RFH's preChristmas season.
Ground conditions at the site consisted of made ground and alluvium for the fi rst 5m, followed by Thames Gravels from 5-10m and then London Clay to a depth of at least 25m.
Site workers installed 50, 900mm diameter CFA piles to 18.8m depth to support a safe working load of 1,500kN and 12, 600mm diameter CFA piles to the same depth for 900kN.
With the 12m long reinforcement cage consisting of 6T32mm main bars, the piles have a factor of safety of 2.5. Design was supported by a single maintained load test on a working pile.
Contingency plans for using two tripod piling rigs were put in place but in the event they were not required because May Gurney managed to manoeuvre the 4.5m wide and 11m long Llamada rig into a restricted access corner of the site.
Following assessment and testing, the access road for the RFH's kitchens was used as a piling platform, with a 300mm to 450mm layer of graded crushed concrete used where the surfacing was incomplete.
The subcontractors's £150,000 piling contract began on 10 January and was completed ahead of programme on 28 January. The team attribute this success to the detailed preparation.
'It's not often you spend 14 months planning a three-week project, ' says May Gurney Geotechnical general manager Steve Longdon.
Taylor Woodrow's project manager Mike Elks adds: 'Installation of the piles went very smoothly, refl cting the early planning and involvement that went into the project.'