Model Tests of Gravity Platforms. II: Interpretation

Abstract

The paper presents the interpretation of five model tests on soft clay performed to qualify the concept of a monobase gravity platform for the Troll field in the North Sea. The test program contained one static, one static after cyclic, and three cyclic model tests. The cyclic tests were run with different moment arms and with widely different cyclic load history compositions. In general, the interpretation supported the calculation procedures that are presently used in foundation design of offshore deep-water gravity platforms on soft clay. The calculated bearing capacities, failure surface locations and failure modes (large cyclic rotations) agreed well with the measurements for all the model tests. The calculated static and cyclic displacements also agreed reasonably well with the measurements. The deviations that did occur indicated smaller calculated displacements than measured. This should be kept in mind in design since it implies that the calculations may underestimate the displacements. However, the deviations primarily occurred at small and moderate loads and may be explained by small imperfections in the model tests (false deformations). Both the calculated and measured cyclically induced settlements were small for the vertical static load applied in these model tests.