Shape effects on undrained capacity of mudmat foundations under multi-directional loading

Abstract

The results presented in this paper systematically quantify shape effects on undrained capacity of rectangular mudmat foundations under multi-directional loading for a practical range of soil shear strength heterogeneity. Mudmat foundations are extensively deployed to support infrastructure for subsea production systems, are typically rectangular in plan, ranging from square to a width-to-length aspect ratio of 0.2, and are subject to multi-directional loading from the attached pipelines and jumpers. The load-carrying capacity of rectangular mudmats on deposits with undrained shear strength linearly increasing with depth is analysed by the finite-element method, and presented in the form of ‘failure envelopes’. The results show that shape effects are significant and are dependent on the degree of soil strength heterogeneity and loading direction (relative to the orthogonal axes of the mudmat). General algebraic expressions are established that systematically define the coupled effects of width-to-length aspect ratio of the mudmats and the degree of strength heterogeneity of the subsoil. Expressions describing the uniaxial ultimate limit states and the normalised failure envelopes under multi-directional loading can be programmed into a calculation tool for automating optimised mudmat sizing for a range of foundation geometry and soil strength heterogeneity.