Case study Peterborough

The Problem
Optera were instructed by Insurers to structurally lift a chalet bungalow in Peterborough that had suffered long term progressive downward movement of the foundations over a ten year period. Despite numerous attempts at mitigation including drainage repairs and vegetation removal, the right hand side of the property continued to drop. A conservatory to the rear of the property had also rotated way from the bungalow. Ground conditions indicated a shallow band of peat over a clay soil.

The Optera Solution
We designed a scheme of bottom driven steel case piles driven across the front, right hand and rear elevations with needles under the existing footings. Using 500kN rated hydraulic lifting equipment, we jacked the right hand side of the bungalow back into level. In doing this, we effectively closed cracks on the front and rear elevations as well as rectifying the visual distortion on the front elevation to the roof line. The front lounge window was so distorted that the welds had broken and there was no lintel above the external frame. We took the decision to deglaze the window but retain the frame during lifting. The building is now straight. Given the length of time that this claim had been ongoing, Insurers were considering demolition and rebuilding the right hand side of the bungalow at a cost of £300,000.00 with additional alternative accommodation costs on top of this.

By opting to lift the building Insurers have saved 75% of their projected spend as well as minimising the inconvenience to the policyholder. Optera are experts in building re-alignment and provide advice and guidance on proposed schemes.

Not every situation is suitable but Optera review existing information and can make an honest assessment of the likely success. In this case, the bungalow had been constructed on an un-reinforced raft which had split down the middle of the building. The shallow nature of the footing made lifting easier. Using laser operated monitoring equipment, we were able to lift the building without creating additional distortions and the result has been a success.

Root barrier
For years, the insurance industry has taken a formulaic approach to clay shrinkage subsidence claims; mitigate, monitor, repair. It’s a philosophy that has served the industry well and notwithstanding the environmental impact of tree removal has provided the correct technical solution to countless subsidence claims throughout the country.

But how many times do we visit a policyholder where the claim has been ongoing for many years, the trees are third party owned, protected and no resolution has been found. Insurers spend on average, £6-8,000 on collating sufficient evidence, site investigations, monitoring and expert reports, not to mention the time spent in placating the policyholder who gradually grows increasingly frustrated with the situation and frequently goes to the ombudsman and is awarded compensation for delays.

So what if there was a different way? Optera are able to offer early intervention in cases where tree removal is perceived as a drawn out process. When third parties or local authorities refuse to remove the trees we know to be the root cause of the problem, why not sever the roots? Early intervention offers the opportunity to mitigate as soon as the site investigation is complete. Using the latest technology in root barrier membrane, we are able to install root barriers in areas previously thought impossible. Our narrow access excavation equipment needs 1.5m working width to excavate and install barriers down to 4m in depth. The barrier is a hybrid copper impregnated membrane which acts both to physically contain the roots but also to chemically repel them. The barrier trench is typically 300mm wide and is back filled with a free draining stone back fill, compacted and allows the surface to be reinstated to its original condition.

Optera have recently completed a 20m root barrier to protect a pair of semi detached garages in South Hampshire from root induced clay shrinkage. The original proposal was to take down the rear of both garages, install 24 open bored piles to 8m and associated needle beams and to rebuild the brickwork.The site investigations indicated clay to 4.2m with a band of alluvium to 4.6m with water and collapsed investigation holes at this depth. Open boring was never possible. Roots were only noted to 2.2m below ground and we consequently were able to install a root barrier around the rear of both garages, continuing up both sides to provide complete protection.

The barrier was completed and the ground reinstated within 5 days. Both policyholders and their respective insurers were delighted with the solution which gives immediate protection from the tree roots and natural rehydration of the ground will now occur during periods of precipitation. Brickwork was taken down and rebuilt owing to the significant distortions which had occurred. In total, the project was completed within 3 weeks with minimal disruption and the home owners continue to enjoy the mature trees.

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The case studies presented below show just a few of the recent projects Optera have worked on.

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