Case Studies - Diggle, Saddleworth: Access problems with drilled piles

In November 2006 we installed 14no. 165mm steel cased piles to an extension at the rear of a property in Diggle, Saddleworth near Oldham.

This on paper would not prove too difficult, however the site geography meant that this would be anything but the case.

The building to be extended was situated high on a hillside with difficult access to the property form the main road. The extension was to be built at 1st floor level behind the main building with access through an archway with restricted headroom, through a garage and up steel steps to the working area. The working area was on a level behind an old stone retaining wall approximately 4 metres high.

The decision was made to install the piles by grundomat due to the access problems. The use of the grundomat also overcame any vibration problems which may have occurred with the retaining wall. Very quickly it became obvious that the geology of the area created problems for the pile installation by the grundomat.

A natural moorland slope ran down across the site. At varying depths of between 2 to 4 metres the local bedrock was encountered onto which the grundomat driven piles were stopping immediately. The rock was fairly un-weathered and as a result the grundomat could not create a socket into the rock that would stabilise the end of the pile. The only option open to us was to drill a socket into the bedrock into which the pile could be driven. The obvious problem being – How do we get the drill rig to a site which can only be reached on foot?

The solution was to use a crane with low headroom to negotiate the low headroom of the archway that also could manage to drive around the tight lane to the building. The crane together with our drill rig and piling rigs were delivered to site and the machines lifted over the building onto the working platform.

The images below show the operation to crane the drill rig up and over to the working area.

The piles could now be pre-drilled into the bedrock in order to create the 500mm socket required to sit the pile into. The DTH hammer operated together with a compressor drilled easily into rock and the images below show the operation of this.

Once drilled the piles were then driven into the socket using the drop weight rig. Following the installation of all the piles the main contractor excavated for the ground beams. Finally we returned to the site to place the reinforced steel prior to pouring concrete using a trailer mounted pump again due to the access problems.