Suction Caisson Response under Tensile and Compressional Vertical Cyclic Loading in Layered Soils-Paper

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The study investigates suction caissons embedded in clay over sand and subjected to vertical cyclic loading, a relevant condition for offshore wind turbine foundations. Centrifuge tests at 100g examined two loading cases with the same tensile minimum load but different average compressive loads. Two-phase finite-element simulations were also conducted to assess the caisson response and pore-pressure behaviour.<br /><br />The experiments showed that average compressive load strongly influences the overall response. With the lower average load, cyclic loading produced substantial net uplift, particularly when tensile cycles exceeded the drained frictional capacity. The higher average load instead generally led to net settlement, despite similar excursions into tension. Tensile resistance involved skirt friction and suction pressure associated with clay-plug uplift and pressure transfer into the underlying sand. In compression, resistance was carried mainly by the skirt and tip.<br /><br />The findings highlight the role of drainage, soil layering, and the interaction between tension and compression. A sufficiently compressive average load, or limited tensile excursions, may help prevent net uplift.<br /><br />The numerical model captured the response reasonably well for the more compressive loading case but was less accurate when tensile loading caused significant plug uplift and soil movement around the skirt tip. Modelling limitations in representing tip resistance led to errors in predicted compressive response and overall displacement. The results provide experimental evidence to support improved numerical modelling and design of suction caissons in layered soils.

Keywords

suction caisson

clay over sand

vertical cyclic loading

offshore wind turbine foundations

centrifuge tests

pore pressure

net uplift

skirt friction

finite-element simulations

layered soils