Seabed movements and their effect on offshore structures

The seabed in many parts of the world consists of very soft clays. These are marginally stable and underwater mudslides have known to be triggered easily by the action of a storm wave or an earthquake. If such a mudslide encounters a fixed offshore structure, the foundation piles will be subject to additional load caused by the moving soil. Consequently an assessment of the seabed movements is important for the design of such structures. An analysis method is described using the finite element program DWAVE. The method is illustrated by a case study. Predictions of the soil movements during a 100 year storm were made. The soil-pile interaction was analysed and revised lateral load-deflection curves for the piles were derived. The effects of deep jack-up spudcan penetrations adjacent to platforms were also analysed. Soil remoulding occurs near the foundation piles. This causes increased soil movements and reduced soil resistance for pile support.