2005 Poulos Lecture “Soft clay engineering: site characterisation and design of shallow foundations and anchoring systems”

Professor Mark Randolph, ARC Federation Fellow

The worldwide trend in the offshore industry is towards ever deeper water, where the seabed sediments mostly comprise normally or lightly overconsolidated soft, fine-grained sediments. This has brought particular challenges in characterising the soil, with much greater reliance on in situ testing, and designing seabed foundation and anchoring systems. The upper 0.5 to 1 m, where the shear strengths may be 5 to 10 kPa or lower, is particularly critical for pipelines in respect of embedment depth and resistance to buckling brought on by temperature changes. The lecture will focus on offshore applications, but address many issues that are very relevant for onshore design in soft clay, in particular site characterisation, including interpretation of ‘full-flow’ penetrometer data, and the effects of strength gradient and geometry on the bearing capacity of shallow foundations. Establishing an appropriate shear strength profile is critical for design, but this is complicated by secondary effects such as strength enhancement due to high strain rates and strain softening during penetration of objects into the seabed. Further applications including plate anchors, and dynamically penetrating torpedo anchors will be described briefly.

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