Soil Failure Mechanism and Capacity of Stiffened Caisson Anchors in Calcareous Silt-Paper

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The study used centrifuge tests to investigate the installation, failure mechanisms, and loading capacity of stiffened suction caisson anchors in calcareous silt. A half-model caisson was observed through a transparent window at 100g, with particle image velocimetry (PIV) tracking soil movement during suction installation and 45° pullout. Two full-scale models were tested at 150g under 20° monotonic or combined monotonic–cyclic loading.<br /><br />During suction installation, soil inside the caisson moved upward, causing heave of the inner soil plug. End bearing was mobilised beneath the skirt tip and bottom stiffener, while little movement occurred outside the caisson. During inclined pullout, PIV revealed a downward-moving wedge on the trailing side, upward soil movement on the leading side, and shear at the skirt tip. This mechanism differs from the combined wedge-and-flow and general end-bearing mechanisms commonly assumed in design guidance.<br /><br />The monotonic holding capacity was about four times the caisson’s dry weight. In the cyclic test, the anchor underwent 500 cycles at a mean load of 50% and amplitude of 15% of the monotonic capacity. It did not fail during cycling, and its subsequent monotonic capacity was 23% higher than the purely monotonic capacity. The authors suggest reconsolidation or changes in soil fabric may explain the increase, but further investigation is needed. The findings provide new evidence to improve understanding and analysis of caisson anchors in calcareous silt.

Keywords

centrifuge tests

suction caisson anchors

calcareous silt

installation mechanisms

failure mechanisms

particle image velocimetry

soil movement

pullout capacity

cyclic loading

end bearing