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Sylvan stabilisation


SUBSIDENCE ON a housing estate in south London has been overcome with a combination of piles and ground anchors installed by Roger Bullivant.

Work at the Sylvan Road Estate in Norwood included a contiguous piled retaining wall next to a garden that was showing signs of failure. The garden is between two blocks of flats that were subsiding because of the instability of the slope they were built on.

A pedestrian access ramp from a road to the garden had also become unstable and had been closed.

Bullivant's initial contract was to underpin the two blocks of flats, an electricity substation and store structure for main contractor J Murphy & Sons. It installed 100 piles of 300mm diameter to depths up to 18m.

For the contiguous piled retaining wall Bullivant created 26 open bore concrete cast in situ piles - each measuring 600mm in diameter - to a depth of 12m. Each pile was formed at 750mm centres with an auger.

The works also allowed the pedestrian access ramp to be reconstructed. Ground was then excavated from one side of the wall before a series of ground anchors were installed about 3m from the top of the wall to provide a suitable restraining force of 413kN per anchor.

Each ground anchor was made up of 3m sections and measured 19m in length when complete. A Klemm 802 rig was used to install each anchor between pairs of piles at five degrees from horizontal down into London Clay.

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