The Problem
A king post and rail retaining wall for a raised embankment to the rear of a timber-framed bungalow on a farm estate had failed following a period of sustained rainfall. The king posts had rotated within the ground, shearing the supporting soil and allowing the rails to rotate forward. In turn, the embankment had slumped and large stress cracks were noted. The embankment was left just 200mm from the rear wall of the bungalow and a large-diameter, high-pressure gas main was also noted to be 1m from the top of the slope.

The Optera Solution
Optera were initially requested to provide a quote to reinstate on a like-for-like basis. As the wall was taken down and the embankment graded to remove the risk of further failure, it became evident that the soil was predominantly alluvial and there was a high water table, only 200mm below ground level at the bottom of the embankment.

We therefore revised the scheme to include 270mm bottom driven, steel cased piles to a depth of 6m which the steel king posts were then cast into with reinforced concrete. The larger diameter of the piles, coupled with the depth of drive, mean that any future risk of groundwater-related shear failure has been removed.

We recycled the reinforced concrete rails which were part of the original structure as they were undamaged and these were placed behind the steel king posts and stacked to form the new wall. Behind this we placed a gravel drainage channel for the full height of the wall with a perforated land drain at the bottom of the wall, which was connected into an existing drain.

Project Conclusion
It is commonplace in claims of this nature for a comprehensive site investigation to be undertaken by structural or geotechnical specialists. We were not afforded this opportunity as any delay in responding to the site issues would almost certainly have led to significant structural damage to the property which had remained undamaged. Through Optera’s swift intervention, the wall was successfully reinstated within a four-week timeframe and within budget and we were also able to avoid damage to the gas main.

The customer forms an important part of our focus and in this instance we were able to accommodate their request to create an additional area to the rear of the property to allow for future expansion plans. The policyholder was delighted with the outcome as were the insurers.

“We revised the scheme to include 270mm bottom driven, steel cased piles to a depth of 6m which the steel king posts were then cast into with reinforced concrete.”

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