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Dunelm carried out the drilling of thirty-four boreholes on a large landslip in County Durham over three phases, to a maximum depth of 47.00mbgl. Drilling was advanced using cable percussion boring through superficial deposits and wireline and conventional rotary core drilling through the rock. Drill bit selection was key to obtain the specified core recovery and several different bit types were used depending on the rock type being penetrated. The client required high quality, full core recovery throughout the potentially disturbed mudstone layers as this was thought to be of the main courses of the slope failure.
The site comprised a 400m section of the B6344, and the surrounding land immediately east of the town of Rothbury. The surrounding land comprised sloping woodland and grazing land, which had been set aside for wet pasture and was classified as a SSSI. As such, access to the site was challenging and required roadways to be constructed into all areas.
Artesian groundwater conditions were anticipated across the site of up to 2.00m and suitable equipment was mobilised to deal with this. However, during drilling artesian conditions often exceeded 7.00m head. Further equipment to deal with the strong artesian pressures was mobilised including the provision of heavy recirculated drilling muds. This on occasion was still not sufficient to manage the flow of the groundwater and we constructed a scaffold platform, up to 7.0m high, around the rigs to balance the groundwater pressures. This enabled the controlled installation of inclinometers and multilevel grouted in vibrating wire piezometers.