Case study Sevens Oaks

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

The Solution
Optera were initially requested to provide a quote to reinstate on a like for like basis. Whilst the wall was initially 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 revised the scheme to include 270mm case driven piles to 6 metres 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 ground water 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 steels 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. The wall was successfully reinstated within a 4-week program and to budget.

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 accommodate future expansion plans.

By acting swiftly, we were also able to avoid damage to the gas main.The policyholder was delighted with the outcome as were insurers.

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