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Dounreay restoration is well drilled operation

ENVIRONMENTAL GEOTECHNICS CONTRACTS

FOUNDATION AND Exploration Services recently completed a hydrogeological and geological study for part of the UK Atomic Energy Authority's £4bn restoration of Dounreay nuclear complex in Caithness, north east Scotland.

The two-phase contract aimed to provide an accurate model of groundwater flow around the D1225 intermediate level waste shaft, to enable a waste retrieval programme to be designed.

Work included refurbishment of boreholes, geological mapping and installation of groundwater pressure monitoring systems, followed by site investigation to establish the stratigraphy, fracture network and hydrogeology of the area around the shaft.

FES installed nine boreholes to between 25m and 220m. Openhole drilling with a 250mm tricone rock-roller was used down to bedrock and the hole lined with 200mm diameter steel casing cemented into place.

Continuous rock cores were recovered from below the superficial deposits and weathered bedrock in seven of the boreholes using triple-tube Geobore S wireline coring.

FES geologists carried out pH/sulphate, slake durability, moisture content and various strength tests on the cores.

Hydrogeological tests included production, discrete sector and pump testing. On completion, vibrating wire piezometers were installed in three boreholes.

Four types of rotary drilling rigs were used during the investigation - a truck-mounted Dando 250, a track-mounted CMV3000, a Comacchio MC1000 and a Comacchio MC405.

A polymer drilling mud was used for all rotary coring and open hole drilling, with the exception of down the hole hammer work.

Work also included thermal conductivity, natural gamma and flow logging measurements and installation of multi-zone Westbay piezometers.

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