Strength increase of a marine clay-steel interface - Implications for Offshore Skirted Structure Recovery

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4. Strength increase of a marine clay-steel interface - Implications for Offshore Skirted Structure Recovery

In offshore geotechnics, besides the shear behaviour of soil the soil-structure interface behaviour has a large impact on the performance of offshore structures. For example, the resistance of suction buckets or piles during installation, loading or recovery is ruled by the contact shear strength between the structure and the soil. Challenges still exist in predicting the appropriate shear strength after rest periods, as experiences during the recovery of suction buckets have shown. A practical example of a suction bucket recovery after 6 years in low plasticity clays is shown here. Between 2 cm and 11 cm of clay sticking onto the skirt have been measured after recovery. This significantly influences the break-out load and weight of the structure to be lifted. As a hypothesis, the undrained shear strength is estimated to be locally higher towards the skirt than the intact strength. To investigate this, strength gain of a marine clay and a marine clay-steel interface is further examined in this work. A sandy and gravelly marine clay is homogenized with considering the pore water composition (mainly the salt content) to ensure the similarity of in-situ properties. The shear strength of the soil and the contact shear strength of a clay-steel interface are determined through laboratory vane tests and interface ring shear tests with rest periods.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

11 - Suction installed foundations and anchors