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Session 4: Ground Movements and Construction Operations |
Integral Geotechnique Limited, Ove Arup & Partners, Bristol, 1 Woodford Close, Nailsea, Bristol BS19 2UH, UK
A conventional ground investigation for an elevated tank at Box Hill near Corsham in Wiltshire, proved 5 m of thinly bedded oolitic limestone, beneath a veneer of fill. Four weeks before the construction works were to be put out to tender in 1986, a plan of the Brewer’s Yard Mine came to light, which indicated that there were old stone mine workings beneath the tanks, at about 17 m depth. A geotechnical reassessment was therefore commissioned.
An examination of the workings revealed that three significant roof collapses had occurred within the mine, directly below the proposed tank. The largest fall had migrated about 3 m above original roof level. It was concluded that future falls were likely. However, an existing elevated tank was located over old workings and although it had been levelled regularly over its 50 year life, it had showed no signs of movement. Consequently a cost-benefit analysis of a number of options was undertaken.
