The M3 motorway will run through a cutting in Barton Sand at Camberley. It is proposed to install sub-soil drainage to lower the water-table, with the object of reducing the moisture content of the sand and ensuring the stability of the earthworks. This report describes laboratory soil moisture suction tests carried out to estimate the reduction in moisture content likely to be achieved. It is concluded that the moisture content will be reduced from 24 to 18 per cent for sand lying more than 2m (7ft) above the lowered watertable. Sand at the completed formation level will remain near its natural moisture content of about 24 per cent unless exposed to dry weather. The time-lag between lowering the water-table and the reduction in moisture content is estimated to be 1-4 weeks but field measurements should be made during construction to obtain a more reliable value for controlling the rate of excavation. (A)

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