Scour prediction in non-uniform soils: undrained shear strength and erodibility

Scour development in non-uniform soils is still an area of great uncertainty and remains a challenge for designing structurally efficient and effective foundations in the marine environment. Scour risk in cohesive soils is made more uncertain by effects such as weathering and time-scale to scour. For large volume installation of foundations such as those related to offshore wind farm developments there is a limit to the amount of detailed geotechnical information that can be collected as part of the project. Therefore, reliance in data such as undrained shear strength, derived from cone penetration tests, supplemented with borehole data collected at a limited number of sites across the wind farm and laboratory analysis of soil samples becomes the principal source of geotechnical information. Hence, the question arises as to whether the undrained shear strength be used as a proxy for the erodibility of a soil as proposed in the approach of Annandale (1995). This paper will present evidence from both field and laboratory measurements of undrained shear strength and scour potential to test the hypothesis of undrained shear strength as a proxy for scour.