Case Studies - Centurion Point, Chester: Difficult access for bottom driven piles

In July 2006 we were asked to install 16no. 220mm piles at Centurion Point, Chester. The piles were required to support a cantilever slab and as a result 8no. piles had to be driven to achieve a compressional SWL of 240kN and the others 105kN in tension.

Two major problems existed on this site. Firstly, all work was inside the building and the only access to the working area was via a goods lift. Secondly, the ground conditions consisted of very loose fill material to a depth of 12 metres overlying local sandstone. These ground conditions would not allow the use of a DTH hammer to create a socket in the rock into which we could drive a pile.

Once delivered to site the piling rig had to be split from it's generator and moved using a pallet truck. The rig was wheeled into the goods lift and lowered to the basement level. The hydraulic hoses were then fed through a cored hole in the ground floor slab and reconnected to the rig.

The solution to the problem with the piles in requiring a socket into the rock was as follows. All 16no. piles were initially driven down to the sandstone with a penetration of approximately 300mm. The DTH hammer was then lowered into the empty pile casings of the 8no. piles requiring the rock socket. The DTH hammer drilled through the pile bottoms and into the sandstone creating a 1 metre socket. The casing of the driven pile eliminated the possibility of any loose fill material dropping down the pile. The piles were finished by inserting a single T25 bar down the entire length and concreted.