Soil Reaction Stresses on Offshore Gravity Platforms

Abstract

The paper summarizes the results of analyses of soil reaction stresses on offshore gravity platforms. Three aspects are considered herein: (1) Stress distribution on individual foundation skirts; (2) horizontal load sharing between skirts and platform base; and (3) contact stresses on platform base. Results of analyses illustrate the effects of skirt geometry, skirt flexibility, and soil parameters on the reaction stresses against the skirts and the platform base. Comparative analyses were done with elastic linear and nonlinear soil formulations, and with plane strain, axisymmetric, and three‐dimensional models. Guidelines for design are proposed for the evaluation of the stress distribution with depth for short and long skirts and the evaluation of contact stresses on the platform base. The three‐dimensional finite element analyses showed that a plane strain model through the center of the platform gives a good approximation of the normal and shear stresses against the skirts predicted by a three‐dimensional calculation. Based on two‐dimensional analyses with a nonlinear soil model, it is believed that the assumptions of skirt flexibility/rigidity are much more significant for the soil stress distribution on the skirts than the assumptions of a linear or nonlinear soil model.