This paper describes a range of techniques for estimating the capacity of offshore foundations, which has always been a main issue in foundation design and remains so today. The paper, however, takes a tack that is slightly out of the mainstream - by emphasising methods of plastic limit analysis rather than more traditional approaches. It begins with a brief history of offshore geotechnical developments, describing how design methods have evolved for shallow foundations and pile foundations, and the types of loads, site conditions and foundation geometries encountered. A number of simple solutions are provided with detailed example problems. This paper proposes that plastic limit analysis methods have the potential to supplement and enhance more traditional methods.

1. Introduction

I am sincerely honoured to be invited to give the inaugural McClelland Lecture. I am humbled by the task before me as I sincerely wish to produce something that Bram McClelland would have appreciated. At first I leaned toward a subject that more characterised his expertise and interest - engineering geology, site investigation and foundation design. On further reflection however I concluded that Bram delighted in developing engineers who followed their own interests, not in his image, but in their own unique ways. That is the kind of leader he was. This epiphany led me to select a topic that has long been a passion of mine - bridging the gap, sometimes chasm, between theory and practice. I believe this is what he would have wanted from me. Estimating foundation capacity has always been a central issue in foundation analysis and design. Various different methods are employed in this practice, many of which involve ad hoc assumptions and empirical models. This paper focuses on one such advancement, plastic limit analysis (PLA), a methodology that is theoretically sound, internally consistent and surprisingly simple to apply.

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