Underpinning from Inside a Building

Problem

The Customer has experienced subsidence of the property due to trees in the back garden and fluctuations in ground moisture levels, causing the walls to move and cracks to appear.

Access to the outside wall was not possible so underpinning needed to be carried out inside the building. In addition to the subsidence, the customer was also looking to redevelop the extension from single to two storeys.

Solution

Using the ABC 400H hand held torque and keeping the powerpack outside the house. The Piles were installed quickly and quietly, underpinning brackets were then fitted and pre-loaded to design load. This was then back filled around the piles and the floor reinstated. The building is now ready to be developed to a two storey.

Easter Glentore Wind Farm

Easter Glentore is a wind farm situated between Glasgow and Edinburgh. This project entailed the jacking of two substation transformer units back to their original level.

The very poor ground was a mixture of soft undisturbed peat along with 5.5m of infilled stone that had over a period settled and caused the substation units to subside on one side. The movement of these units, both weighing in at around 12t was putting the underground electricity cables which are fed from the wind turbine at risk of damage.

ABC Anchors were asked to install screw piles along the subsiding edge of both substation units and bring them back to level using underpinning jacking brackets.The project needed careful planning due to the potential damage to the underground cables during the pile installation and the cost of having the wind turbine shut down for longer than necessary.

As always with the underpinning process, careful excavation to expose the footings was the first operation. The units were both set on 300mm thick concrete slabs so once the underside of these had been exposed localised pockets could be cleared away under the edge of the slab to allow for the jacking plates. The piles could then be installed using the ABC 500X torque head mounted on a 5t excavator. 4 piles were used on the smaller unit and 7 and the larger one. All the piles needed to be installed to 4kNm of torque which meant they were 6m deep in order to penetrate the hard undisturbed layer which started at 5.5m.

Once all the piles were in place the jacking brackets could be fitted and the jacking up process could begin. Care is always taken during this process to ensure the structure is loaded equally and no damage is incurred.

40kN hydraulic jacks were used on each pile making the leveling of the units a simple operation. With the piles all preloaded equally and the units back to level the jacking brackets could be locked in place using the M16 threaded bars and the jacks removed.

Finally the excavated soil is replaced with a type 1 scalpings and compacted to ensure there is no movement between the piles and the foundation.

Customer Comments

This was our first time using a screw piling system and I would highly recommend it, I would give the guys a 10/10!

Darren Hendry

Conservatory Underpinning – Cooke Brothers

The conservatory had dropped approximately 60mm and opened up the brickwork. When I installed the Screw-Piles and used the underpinning bracket and jacks, I was able to lift the complete structure back to original height.

I used my own Micro Digger as a powerpack for the 400H driver head.

The gap in the brickwork was closed, windows and doors that were jammed out of alignment all now work perfectly.

I was very happy with the serviced provided by ABC Anchors, they were very accommodating with shipping the equipment over to me in northern Ireland. I would recommend the screw pile system to anyone with similar foundation issues. it worked very well.

Allistair Cooke

Underpinning – Conservatory

A conservatory which had been unsuccessfully underpinned using concrete, has now been restored to its original level using 60R helical screw piles.

Initial soil tests indicated that competent ground would be located at approx. 2m depth. However, inspection of the failed foundation and the local presence of trees shed some doubt on this information.

Pile installation was very quick with all equipment hand portable on site.

On this site conventional foundations looked OK but were in fact terminated just above a layer of poor ground.

A two man crew took 1½ days to complete the operation.

Piles were positioned to avoid a number of underground services/utilities.

 

Using the ABC 400H hand held driver, which has a continuous torque read out, our operators discovered that the competent ground overlay a 2m thick band of soft material. The piles shown were driven to depths of 5-6m before achieving satisfactory installation torques and standard underpinning brackets were then installed and carefully jacked using our 40KN/pile system.

The photos show the ground beam has now lifted from the conventional concrete underpinning and is restored to its original level.

Foundation Repairs

Foundation Repairs – Underpinning

Subsiding properties are becoming more common. This is due to new buildings and extensions being built on insufficient foundations or shallow footings on clay soil. We have developed a system which can stabilise the subsidence and in some cases lift the building back to its original level.

The process involves digging around the outside of the failed foundation to expose the base of the concrete foundation. Pockets are then dug under the foundation at 0.8m-1m ctrs. Where the pockets have been dug, screw piles are installed to torques in excess of 3kNm. Piles need to be installed into stable ground. Jacking plates can then be fitted to the piles and lifted using hydraulic jacks. Once all of the piles are preloaded equally, the process is complete with the building stabilised and in some cases lifted back to original levels. Trenches are then backfilled with soil or type 1 if extra support is required.

Key Features

Can be hand installed for sites with limited access
Minimal disruption to property and surrounding area
Noise and vibration free operation

We have worked with numerous window companies to support and lift subsiding extensions and conservatories.

Access all areas – Underpinning with Helical Piles

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.”