Utilising the jack-up platform 'Mytilus', the work has been carried out in two phases. In the first phase, over six weeks on behalf of Global Renewable Energy Partners (GREP), geotechnical data was obtained for use in the final foundation design for 21 of the turbine monopiles. At five of the locations, FES drilled boreholes to depths of around 50m using a Dando 2000 cable percussion rig.

On encountering London Clay, the boreholes were extended by Geobore S triple tube wireline rotary coring to the required depths. Samples were taken at 1m intervals during the CP boring and 1.5m cores recovered.

Soil and core samples were transported on completion of each borehole to Fugro's laboratories for physical and analytical tests.

To cover the remaining turbine locations and the extremities of the 7km by 3km development grid, in-situ tests were completed at 17 locations where CPT tests to depths of around 50m were recorded. Seismic cone tests were performed at two of the locations, plus conductivity profiles at two others. The CPTs were performed in a push, drill, push sequence to achieve the necessary depths.

In the second phase of the works, FES was commissioned by Danish contractor M T Hojgaard, acting on behalf of their client NEG Micon, to complete the investigations for the remaining turbines. This involved carrying out 11 CPTs to depths of 34m.

During each phase of the work, Mytilus was towed to position at each location by the tug Herman Senior , owned and operated by H&S Marine. Care had to be taken when jacking up the platform at some locations to avoid punching through and when raising the legs from the highly cohesive London Clay.

The work was carried out 24 hours per day, with crew changes made using either the tug or a RIB out of Whitstable.

MJ Information No: 19415