PILING SERVICES LONDON
Mini SFA Open Bore Piling, Mini SFA Hollow Stem Piling and Steel Cased Bottom Driven Piling
We offer the following Piling Services across London and the South East
- Mini segmental flight auger(SFA) open bore piling
- Mini SFA Hollow Stem Piling
- Steel Cased bottom driven Piling
What are they?
1.Mini SFA Open Bore Piling
Commonly used in areas with good, dry, stable ground conditions.
Open bore or open hole as it’s commonly known as basically means that the pile stays open and intact after drilling.
How does it work?
The piling rig is tracked onto and set up over each pile position.
The pile is drilled (bored) using 1m long screw shaped sections of cylindrical auger, of varying diameters depending on the design.
1 metre at a time, the ground is drilled, adding on the following 1 metre sections of auger as the pile gets deeper.
Each auger then “screws” into the ground, which brings up the muck/spoil with it, gradually forming your pile.
This procedure continues until the required depth (as per the design) is reached, all augers retracted and dismantled, eventually forming an “open hole”.
Reinforcement is added, and each pile is then filled with concrete from ground level, at the end of each day.
Mini Open Auger Piling tends to be our most common and cost effective piling method, due to our ability to achieve the required higher loads at depth for each foundation, especially in harder grounds in and around London.
2.Mini SFA Hollow Stem Piling
Commonly used in areas with unstable ground conditions, where a dry open pile cannot be constructed.
How does it work?
The piling rig is set up over each position as in open bore piling, and the method of drilling is essentially the same. However, in Hollow Stem piling the difference is in the augers.
The centre of the Augers, i.e. the Stem, is hollow.
What happens is in this instance, when the required depth is reached, a cementitious grout, which is sand, cement and water mixed up by hand on site in a Grout Pump, is “injected” by pumping the grout down through the core of the hollow stem Augers.
As we retract the augers, in 1m sections, the grout fills up the void created by the drilling, stopping the weak sides to cave in, therefore creating an integral pile.
Whilst the grout is still wet, the reinforcement is immediately added.
This is a much slower process, as only a section of pile can be pumped and formed each time, with the pump mix needing to be carefully mixed and consistency maintained.
This is also a costlier process, as extra material is required, with an element of wastage allowed for as well.
Extra equipment is required, i.e. the Grout pump as well as a jet wash to wash down at the end of each; as well as extra labour to man the pump, and also an extra man on the rig, those augers are heavy!
Finally, it’s not a pretty sight, hollow stem piling, is a hard and messy job – so be prepared for this. However, you can be assured that we leave your site clean and tidy once finished.
3.Steel Cased Driven Piling
Commonly used in areas of bad, loose, wet soil conditions, and in areas with a high water table.
How does it work
Steel cased piles are exactly as they sound. Piles constructed using steel casings.
Each type of casing is of variable diameter, depending again on the pile design.
Steel cased piles are predominantly designed to give you a good end bearing on the pile, meaning transferring the load required for your foundation down onto and into a firmer strata or soil type.
A steel cased pile can be driven into the ground using a Drop Hammer rig, which is a heavy weight on a tracked rig, or from an A Frame with a winch on it, dropped from a height, banging the case into the ground.
It can also be driven by percussion, using an air compressed weight, known as a Grundomat.
Steel casings are commonly 2m in length.
The first casing; the ‘leader’, comes pointed and sealed at one end.
About 500mm of ballast and cement known as the “pug” is mixed dry by hand and poured into the leader, in order to stop the weight getting stuck in the point, or more importantly, breaking through and splitting the point when dropped from a height, and it getting stuck in the ground.
This is then driven into the ground.
The second section of casing, known as the “follower”, is open at both ends.
One end slots into the top of the follower, and a continuous weld around the joint forms a watertight seal.
The weight is lifted back into position, and the two sealed casings are now driven deeper into the ground together.
This process is continued in 2m sections, until a “set” is reached.
The set is part of the pile design and determines when the pile has been driven into the ground enough.
As always, reinforcement is added next, and the pile is concreted from the top at the end of each day.
Steel Cased Driven Piling tends to be the cheapest method of piling that we offer.
Generally used for smaller extensions, which require lightly loaded foundations.
To summarise
Unfortunately, it’s not you (or us, to some extent) who can decide on the right method of piling for your project. It’s all down to the ground and soil conditions of where you are building. What type of soil you have and where you live which will determine the best pile for your project.
However, at Brandon Groundworks, we can assure you we will endeavour to find the most cost effective and efficient way to get your project set up, on its feet and out of the ground. Choosing the right type of piling is critical – as it will have a long term effect on your building and this must be chosen correctly (and not be decided by price.)