Contractor Barhale has put a piling hammer to unusual use, driving a 600mm diameter shaft to relieve ground water pressure. The shaft has been installed to drain off water building up inside a collapsed mine adit at the now disused Roman Gravels mine near Hope, Shropshire.
The access adit failed in 1999. Ensuing subsidence forced temporary closure of the nearby A488 trunk road, at the same time slowing migration of water through the mine.
Fearful of further damage through increasing water pressure, Shropshire County Council appointed tunnelling specialist Barhale to provide a permanent solution. Barhale used a Numa pneumatic piling hammer adapted by dealer Iseki to drive a steel pipe 53m at a rake of 1:26, into the adit from a neighbouring stream.
'As ground water rose in the mine, it could climb the pipe and discharge' says Barhale mechanised tunnelling manager Graeme Monteith.
The ground through which the drain was installed is heavily fissured mudstone, siltstone and sandstone.
Head of water in the stream was 3m.
'The ground was too hard for a conventional microtunnelling machine, ' adds Monteith. 'And the risk involved in hand-driving a timber heading into the adit from a new shaft was too high.
Iseki's converted pile hammer has been used successfully in Finland, so was a proven method.
INFOPLUS Iseki tel: (01789) 292227