PROBABILISTIC STABILITY ANALYSIS FOR DEEP-WATER FOUNDATION

A probabilistic model for stability analysis of a deep-water, gravity-based platform foundation on clay is defined, based on theory for wave loading in conjunction with conventional shear surface considerations. An advanced total stress analysis method is applied for representation of the undrained shear strength of the clay, and simple modifications to account for effects of strength degradation caused by cyclic loading are included. The probabilistic model accounts for uncertainties in loading as well as in soil properties, and model uncertainties also are considered. The practical application of the model is illustrated by presentation of calculations for a typical foundation, and the foundation of a concrete monotower at a Norwegian Trench location is considered as an example. This foundation consists of a base slab, resting on the sea floor, in combination with vertical skirts penetrated into the clay at the site. Probability calculations are performed by a first-order reliability method. A sensitivity study is included.