All Foundations completed a contiguous bored pile wall and load bearing piles using two Soilmec CM50 CFA Rigs as part of the expansion of Unilever's production facility at Port Sunlight on The Wirral.
Due to the fast track nature of the project All Foundations were appointed on the basis of preliminary drawings with a view to developing construction designs as the work progressed. The limited Ground Investigation data for the site extended to only 14 metres depth and showed firm to stiff clays across the site.
One of All Foundation's early recommendations was to carry out further Site Investigation Boreholes which resulted in the identification of the presence of sandstone bedrock at a depth of 20 metres. This discovery allowed All Foundations to pass on considerable savings in terms of pile lengths and provided certainty in the overall cost for the project and timeframes.
This element of the project consisted of approximately 200No 750 mm diameter piles in an enabling package to reduce the existing site levels whilst providing support to internal service roads. The piles were 11 metres long, extending to 20 metres where necessary to support column loads.
Retained wall heights of up to 5 metres were designed in cantilever using the basement slab of the final structure to act as a low level prop in the permanent long term condition. For heights up to 7 metres the wall was propped at capping beam to limit deflections to acceptable levels. In locations where the structure was unable to provide this support, buttress piles were installed at the front of the wall to provide the necessary restraint.
Once the contiguous wall was sufficiently advanced a second CM50 CFA rig was brought on site to commence 500No load bearing piles from the reduced level platform.
All Foundations proposed 450mm and 600mm piles for working loads of 950KN and 1700Kn respectively taking advantage of the underlying sandstone.
As the programme did not allow for preliminary pile tests to be carried out in advance, All Foundations carried out pile settlement calculations to show predicted values of less than 5mm at SWL. These low values were critical to the performance of the building due to the cyclic nature of the loads imposed throughout the design life of the facility. These predictions were successfully verified by a number of static load tests, performed by All Foundations, on installed piles.
In order to accelerate the bearing pile programme, a seven day working schedule was implemented to make use of both CM50 CFA rigs once the contiguous wall was complete. The package of work was then extended to include a further 150No piles for a tank farm and 50No piles for pipe racks.
The total overall subcontract duration was 20 weeks, with a final value of £0.8 million. The key to the successful delivery of this project was early piling contractor involvement and flexible and collaborative working arrangements between all involved parties.