Using helical screwpiles to underpin buildings suffering subsidence offers an alternative solution to concreting.
The practice of underpinning buildings with pumped concrete can, in some circumstances, disturb the ground and, in extreme circumstances, make the original problem of subsidence worse.
Using steel screw piles to overcome subsidence is a popular solution, since they can sit in good competent soil at depths of 2m-3m or deeper.
Director of screw pile supplier ABC Anchors Richard Robinson explains: “Subsidence generally occurs in soils that are ideal for screw piling. If the ground is so hard that a screw pile won’t go in, it is unlikely that subsidence will occur. A simple handheld soil probe will determine soil classification data allowing the most economical pile for the job to be designed.
“Where contaminated soils are overlaid with good soil, screw piles can also provide an excellent solution without arisings. In areas sub· ject to flooding, the screw pile will also resist multi-directional loads.”
One of the biggest issues surrounding underpinning projects is that of access. There is often limited room for equipment, and for home owners there is understandable concern if the work must be carried out from within the building. For these jobs, work has been made easier through the introduction of handheld drivers for the installation of screw piles.
Robinson, who has 25 years’ experience of designing handheld drivers coupled with eight years’ experience of manufacturing screw piles, has developed a handheld screwpile driver that uses a hydraulic drive system to overcome installation problems.
“Existing drivers use a heavy motor/gearbox unit at the top of the pile,” he says. “This means that not only do operators have to lift the heavy pile into a near vertical position, but the drive and torque reaction arm has to be lifted 2m in the air as well. This procedure is potentially hazardous and usually taxes the strength of operators to the limit.
“As the pile travels further into the ground, and especially when an extension has been added, the increasing torque reaction tends to force the head of the pile towards the operators. This is a further hazard and exacerbates the problem of using foot controls in muddy, slippery and uneven sites.”
Electric handheld 110 volt mains or lower voltage battery-powered units can provide lighter and more convenient solutions, Robinson says, but they can lack the oomph needed to construct deep foundations.
Robinson’s new ABC 400H Hydraulic Driver uses a standard 301 140Bar power pack with a hydraulic drive system. Having a separate hydraulic power pack with long hoses allows the operator to still work in confined spaces.
“While the 400H Hydraulic Driver still isn’t super light, it’s much easier to operate,” says Robinson. The handheld controls permit logical operation and offer immediate control, making for safer and more accurate installation rather than chasing foot controls in muddy trenches, which can be dangerous.
The new driver permits the installation of 3m or even longer piles in one piece without the use of extensions, saving money and time.
Robinson adds: “Because the handheld hydraulic control is so sensitive too, piles can be installed within +/-1.5mm of correct depth. This makes the formation of precision foundations much easier.”