The Lynn and Inner Dowsing sites cover areas of approximately 2.5km by 4km and 2km by 5km respectively, with water depths between 6m and 13m below LAT.

Soils encountered included Holocene sediments above Boulders Bank Formation sands and sandy clay, overlying cretaceous chalk.

The investigation involved several phases. From the survey vessels Voe Venture and Telco Baltic , Alluvial Mining deployed an 8 ton thrust seabed mounted CPT and a 6m vibracorer to obtain geotechnical data at 16 locations on the Inner Dowsing site, 25 locations on the Lynn site and 20 locations along the cable routes. The Voe Venture was used for the cable routes while Telco Baltic did the remainder.

Two jack-ups were used. The FES1 is a C-5 series Combifloat charted from Combifloat in the Netherlands while Mytilus is owned and operated by Alluvial Mining.

From these, FES constructed 29 boreholes to maximum depths of around 50m. Cable percussion techniques were employed in the upper cohesive soils, supplemented by rotary coring with a wire-line Geobore S system in the underlying chalk. In the upper cohesive soils a number of Standard Penetrometer Tests (SPTs) were completed and open-tube 100mm samples recovered and sealed to preserve their natural moisture content.

In the rotary part of the boreholes, FES conducted further SPTs within the weathered chalk to correlate with the core descriptions.

High pressure dilatometer tests were also carried out in six boreholes to measure the in-situ strength properties of the chalk.

As the sites were too far from the mainland for the convenient short time rotation of the crews, the accommodation barge Sirius B was chartered for the duration of the fieldwork. This provided offshore accommodation for up to 22 persons, sufficient for both jack-up crews and client's representatives. Both jack-ups were serviced by a tug in full time attendance on site. On occasions when weather conditions deteriorated the tug moved the jack-ups to a sheltered location.

FES subsequently completed a series of geotechnical soils tests in their UKAS accredited laboratories, which were supplemented by chemical analyses at an independent specialist laboratory.

MJ Information No: 20771