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Metadata: Hornsea Project Three Offshore Wind Farm: Stage 2 Geoarchaeological Assessment of boreholes collected for Kittiwake Compensation Scheme at the Lowestoft and Minsmere sites.

Abstract:

Boreholes were collected by Fugro Geoservices Ltd between the 18th May and 12th June 2022. Seven boreholes including one bump-over were drilled from two moonpools from the JUB Aran 250 (Fugro 2022). Three boreholes were performed from moonpool 1 which was dedicated to cone penetration testing (CPT). Where the CPT equipment had reached its limitation due to ground conditions, open hole drilling and spot sampling were utilised to advance the borehole to target depth. Four boreholes, including one bump-over, were performed from moonpool 2 which was dedicated to sonic drilling and core liner sampling for archaeological preservation (Table 6.1). Sonic drilling was performed using the CRS XL170 Max duo rig. Dynamic sampling and rotary open hole operations were performed using a Fraste Multidrill. Dynamic sampling was performed using steel casing of 150 mm diameter to stabilise the borehole. Open hole and sonic drilling were performed using the Geobor-S wireline triple barrel rotary coring system with a polycrystalline diamond (PCD) compact coring bit to recover core samples of 102 mm diameter and up to 1.5 m in length. Twenty-four samples were taken for archaeological assessment using downhole coring operations performed with the Geobor-S wireline triple barrel coring system. Core samples of 102 mm in diameter and up to 1.5 m in length were recovered within clear plastic liners. The core catcher at the bottom of the inner core barrel was selected according to the expected ground conditions. Catchers with longer fingers were used to increase the recovery in coarse grained soils, but the number and length of fingers were reduced where this was considered likely to cause disturbance to the in situ soil. After recovery of the core liner samples to deck, the samples were preserved for archaeological testing. The ends of the liner were logged in accordance with BS EN ISO 14688:2018 (BSI, 2018b) and BS 5930:2015 (BSI, 2015), and were then capped, sealed and clearly labelled with top and base indications and depths for photographing. Archaeological samples were taken at the instruction of the onboard client representative and stored separately from the geotechnical samples. All intact cores were transported to COARS at the University of Southampton for geoarchaeological sampling and assessment. Geoarchaeological recording was undertaken at the British Ocean Sediment Core Research Facility (BOSCORF), at the National Oceanography Centre Southampton. Cores were carefully split using a GeoTek Core Splitter. Cores were split longitudinally, with one half retained for archival purposes. This was carefully wrapped and stored in a light-controlled environment, should luminescence dating be deemed necessary. The other half of the core was cleaned and subject to high resolution line scanning using a GeoTek Multi-Sensor Core Logger - Core Imaging System (MSCL-CIS). The MSCL-CIS generates high-resolution, depth-registered images that can be magnified to show millimetric detail. RGB colour data was also collected prior to any colour changes that may occur within the samples (e.g. through oxidation). The results have been tabulated and a summary of the core sections supplied for the Stage 2 assessment were provided. Geoarchaeological descriptions of the samples from each of the cores are also provided.

Data holder:

Archaeology Data Service

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