The response of suction caissons in normally consolidated clays to cyclic TLP loading conditions

Abstract

This paper describes a series of seven cyclic loading test performed in a centrifuge to evaluate the behavior of steel suction caissons under uplift loadings with soil conditions typical of deepwater Gulf of Mexico (GOM). Suction caissons are large cylindrical foundation units installed with active suction after partial penetration by deadweight. They derive most of their uplift resistance from passive suction. The tests were performed to simulate a prototype caisson with a 50-ft diameter and about a 100-ft penetration below the mudline. A primary objective of the testing programs involved the application of cyclic loads representative of the actual loads predicted for a deepwater Tension Leg Platform (TLP) during a design storm. Tests were conducted for a range of inclinations from vertical including: (1) purely vertical, (2) at a 6 inclination, and (3) at an inclination angle that varied during the test. The results obtained from these tests established the combination of the cyclic load ratio (cyclic load divided by the static uplift resistance) and the number of applied cycles that cause failure of the foundation. For cyclic load ratios of 0.48, 0.34 and 0.27 with no fixed static load the number of cycles required to cause failure were approximatelymore » 100, 500, and 1,000 respectively. The tests where the inclination angle varied experienced the most reduction in capacity. Finally a 55-ft diameter by 110-ft long caisson in normally consolidated soils was shown to satisfy design criteria for a 100-year design storm in the Gulf of Mexico.« less