Upper Bound Analysis of Bearing and Overturning Capacities of Shallow Foundations in Soft Clay

Abstract

This thesis presents a method to calculate the bearing and overturning capacity of a shallow foundation installed in soft clay using the upper bound method of plasticity. Mudmats are commonly used shallow foundations in offshore projects and are often eccentrically loaded. As economics and project requirements change, mudmats have evolved from simple circles and rectangles to more complex geometries. Computing the bearing and overturning capacities of such complex geometries using existing methods outlined in API procedures becomes difficult, as these procedures have been established for simple shapes. FEM is an alternative and established method for analysis, but these programs can be costly.

In this thesis, the procedures for analysis using the upper bound method of plasticity are outlined and used to compute the bearing and overturning interaction for several foundations of varying shapes and undrained shear strength profiles. These results are compared to output of the FEM analysis program ABAQUS for validation.

The conclusions of this case study are that the upper bound method of plasticity provides a reasonable prediction of the bearing and overturning capacity of an eccentrically loaded mudmat foundation, though considerations should be made when significant torsion or overturning moments in multiple directions are expected.