House and flat building for a new residential estate in Dudley required cutting into a slope to maximise the development's footprint but something had beaten client Taylor Wimpey to the site and taken up residence,

Phi Group Regional Director Julian Fletcher says it all comes down to timing when working around the urban badgers that had moved into the made ground embankment running along the edge of the site. "You can't disturb them between November and June when they are breeding" he says. "What Taylor Wimpey said to us in September was your price is good as long as you can finish part of it in October."

Phi Group came up with a combination of techniques for the project but decided on its timber product Permacrib for two areas, including the part where the back and white burrowers had made a home.

This comprises 1m deep timber cribs built on top of one another and filled with graded granular infill speed was of the essence to beat the clock and get a retaining solution installed before the badgers turned their minds to more amorous thoughts.

A good thing about Permacrib is the procurement times that can be just two weeks" says Fletcher. "So we were able to start on the first week in October and finish this first phase two weeks later."

Fortunately, considering the time available, this first section of the timber crib retaining wall is relatively low, at just 3.5m high, and runs for about 100m.
Phase two is a taller prospect and includes wall sections rising to 9m in places. Typically, for such heights, site workers would install the timber retaining wall at multiple depths - placing layers of cribs one in front of the other along the face. But although it often acts as a gravity wall leaning at up to 1:4, at this site it is a single depth.

Fletcher explains that the problem is not that a multi-depth wall would not support the slope. It is that contractors could not cut the slope back to install it without suffering a potential collapse.

This meant it was necessary to install soil nails up to 9m into the face of the cut (typically 6m) as site workers re-profiled the slope from the top down.  Over 5000 linear metres of these nails were planned, but more ended up being used as the slope was cut back further than Phi Group had expected. This has seen extra long nails with an additional 3m being installed in places to account for the space between the 76º crib wall and the cut face of the slope. The nails are at 1.2m vertically, with the longest being 12m in the area where the slope was overcut.

Phi Group installed soil panels on the third area of the cut with a 60º face. Along with the phase two Permacrib work this has created a 1200m² wall. The choice of a different face using soil panels was intended to offer a green vegetated finish. But this has changed following the client's decision to have 150mm deep wire mesh panels filled with crushed rock for cost-saving reasons, as well as it being maintenance free compared with a heavily planted face.