On behalf of E.On UK, the definitive geotechnical site investigation project for the offshore wind farm Humber Gateway was completed off the East coast of the United Kingdom, near the Humber Estuary.
The client required 100mm diameter high quality samples from the boulder clays and the cretaceous chalks allowing the engineer to complete the design of the mono-pile foundations. The works included a cable route survey, an UXO detection campaign and the delivery of an interpretive geotechnical report
The campaign incorporated 60 CPT’s as well as a dedicated soil sampling and an in-situ borehole testing campaign, 20 boreholes were sampled, and 9 had in-situ tests executed. The in-situ testing consisted of HPD and PS Suspension logging tests. CPTU testing was executed from the self-elevating platform “Vagant”, using a hydraulic penetrometer pusher with a maximum nominal thrust capacity of 300kN and a cone tip capacity of 150kN. Utilization of a 300kN thrust capacity enabled a reduction in the number of over-drills per borehole location from 2-3 over-drills to 0-1 over-drills.
In stiff cohesive clays and chalk GeoborS triple wireline core drilling was used as sampling method, providing 102mm diameter samples. The sonic sampling method was used as sampling technique in non-cohesive materials (e.g.gravel and loose sand) providing high sample recovery rates.