Piled Basement in Banbury, Oxfordshire
To provide 81 number 300mm dia hollow stem piles to 9.0m to form a Contiguous Piled Retaining Wall, allowing for the patio area to be enlarged, by excavating the bank at the rear of the house. The Contiguous Piled wall also forms the steps to lead from the drive down to the patio. The bank is made up of clay, with layers of ironstone, and in most areas is very soft with running water, which is why the chosen piling system is Hollow stem.
The Hollow stem Piles were grouted (a concrete substance made up of sharp sand and cement at a very strong ratio) onsite with a pump and batched by hand. The cages were pre fabricated and consisted of two sections to gain 9.0m, which are bolted together using high strength wire rope clips, which are then plunged through the newly formed pile that has been grouted as the augers have been removed.
Photo of drawing, with the black dots showing the Contiguous Piles, forming the retaining walls and steps.
Pile positions clearly set out and numbered, by client ready to commence piling.
The PPS Unwin Kitten rig being used with 300mm dia Hollow stem flights, a very powerful yet compact Piling Rig, with grout hose to rotary head.
As we are pumping grout to the bottom of the pile, the water in the pile is forced to surface, making the site very wet, so a good piling mat is needed, to maintain a stable platform for safe manoeuvrability and consistent verticality of the piles.
Continuing the Contiguous Piled wall through restricted areas is no problem, even with delicate masonry and protected trees undamaged.
Although the clay looks very good from this photo, in some areas of the Contiguous Piled wall, we came across large boulders of Ironstone (Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron compound from which iron either can be or once was smelted commercially). Which is extremely hard and very common for this area of Oxfordshire; we were unable to auger through these obstructions which were located around 4.0m from ground level, so excavation was not viable. With discussions and transparency from us at Advanced Mini Piling Systems with the client, we were able to agree a solution for the obstructed piles numbering 7 in total. Ours and the clients engineers omitted the 7 number piles and redesigned the R/C works.