Abstract

The increased cost and potential difficulty of pile driving in the deeper waters of the Gulf of Mexico (GoM) have been the impetus for exploring alternative foundation types. One viable option that presented itself to the petroleum industry was the suction caisson foundation. Floating offshore structures are subjected not only to static uplift loads due to buoyancy, but also to low frequency cyclic loads from environmental conditions. An experimental program was undertaken to investigate the behavior of model suction caissons under simulated location-specific geotechnical and environmental conditions of the GoM (E1-Gharbawy, 1998a). The effects of such parameters as the magnitude of the peak cyclic load, the inclination, and frequency of the applied load on the number of cycles undertaken by the caisson to undergo "excessive" displacement were examined. At peak cyclic loads greater than the long-term capacity of the caisson, caisson displacements occurred at rates proportional to the magnitude of the peak load. The static, long-term capacity (LTC) of the caisson was found to provide an upper limit on the peak cyclic load that could be withstood by the foundation before undergoing significant displacement. The effects of load inclination and oscillation frequency on the cyclic capacity were of particular interest when the peak cyclic load exceeded the long-term capacity of the caisson. The relationship between the number of cycles to a given displacement and the magnitude of the peak cyclic load was also a function of both the load inclination and oscillation frequency

INTRODUCTION

Before cyclic tests could be performed, the static pullout capacity of the model caissons under drained and undrained conditions had to be established (E1-Gharbawy and Olson, 1998a). Under fully drained conditions, shear failure occurred between the caisson wall and the soil; the caisson pulled out clean on both the inside and outside.

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