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Firm Foundations for the Isle of Grain
01 Feb 2005
Land and marine geotechnical investigations for a proposed LNG terminal, including an unloading jetty and pipeline at Horseshoe Point on the Isle of Grain in Kent UK, has been completed by Fugro Engineering Services (FES) for Skanska Whessoe .
Skanska wished to establish the elevation of the London Clay and the thickness of river alluvium over a 200m by 400m grid to confirm their pile design. From the self propelled jack-up Coastal Explorer , FES obtained continuous soil profiles to depths between 7m and 32m using a core penetrometer (CPT) and drilled eight cable percussion boreholes to maximum depths of 45m.
On land, FES employed a Dando 2000 cable percussion rig for two 40m boreholes, supplemented by four piezocone CPTs to a depth of 35m.
Standpipe piezometers were installed in the boreholes within the gravel strata overlaying the clay to perform rising and falling head tests.
During both land and marine stages, SPTs were taken in the soft, cohesive granular soils and London Clay. Vane tests were carried out in the soft alluvium and undisturbed U100 samples recovered for subsequent analysis in Fugro's laboratories.
The site runs alongside the former BP Grain Terminal and close to a Site of Special Scientific Interest. The investigation had to be completed to a strict timescale to avoid winter breeding season for migratory birds and there were tight controls on the discharge of any borehole arisings in the estuary.
The London Clay foundation was encountered across the site at elevations of between 19m and 27m below chart datum, overlain by mainly soft river clays, loose silts and sands.
MJ Information No: 20330
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