Engineering properties of stiff Bolders Bank glacial clay till from Cowden

• Main Authors: Ushev, Emil R., Liu, Tingfa, Jardine, Richard J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Society for Underwater Technology 2023
• Subjects: Norwegian Sea
• Online Access: https://hdl.handle.net/1983/70065be5-1e7c-4f2d-aed4-12ae1a163dc0; https://research-information.bris.ac.uk/en/publications/70065be5-1e7c-4f2d-aed4-12ae1a163dc0; https://research-information.bris.ac.uk/ws/files/381794314/Ushev_et_al._OSIG_2023.pdf; https://sut.org/books-and-conference-proceedings/offshore-site-investigation-and-geotechnics-2023-conference-proceedings/

Many Baltic, North, and Norwegian Sea oil, gas and offshore wind structures are founded on glacial tills, as are some US developments. This paper presents an overview of coordinated programmes of monotonic and cyclic laboratory testing on natural low-to-medium plasticity, high OCR, stiff Bolders Bank clay till. Profiles with depth of index properties, undrained shear strength and non-linear stiffness are compared with in-situ measure-ments and their effective pressure level dependency reported. The till’s stiffness anisotropy was investigated by high-resolution small-strain stress probing tests and through hollow cylinder apparatus (HCA) tests which also established its shear strength anisotropy, which is quite different to that of low OCR clays. The till’s cyclic re-sponse was characterised over a wide range of mean and cyclic shear stress combinations, identifying stable, metastable and unstable styles of strain accumulation and stiffness response that reflect the cyclic stress paths’ engagement with the till’s Kinematic Yield Surfaces (KYS) and proximity to its monotonic failure envelope. The experiments highlight new insights, including the till’s relatively stiff and strong response to horizontal loading, that have important practical implications and provide a basis for developing and calibrating more representative constitutive models for offshore analyses and designs at till sites.