Identifying Some Knowledge Gaps in Marine Foundation Practice - A Design and Construction Perspective
Authors: Houlahan Gerry T. , Doherty Paul , Stevens Robert 
Published: April 2012

The Marine Foundations Committee of the Deep Foundations Institute in theUnited States (DFI) has been actively advancing the state of the art in marineapplications of deep foundation design and construction for the past 8 years. The scope of these efforts has ranged from driven pile foundations similar tothose used in offshore applications to those used only in traditional onshoreand near shore marine structures. There is now a significant overlap betweenthese two distinct reference sectors of technology. This paper presents theopinions of the committee in identifying the major recent advancements, specifically in the sector more similar to offshore driven pile technology. Furthermore, remaining areas of uncertainty are identified and possiblesolutions are suggested in order to fill these knowledge gaps.

Applications of driven piles as diverse as offshore oil & gas platforms, large bridges, ports and harbours, and the offshore wind industry are oftenseen to share similar design and construction issues. However, in many aspectsthese sectors suffer from unique and specific design and constructionchallenges that are not addressed individually. This paper explores the need toinvestigate some of these recent issues that have arisen in practice. Theauthors discuss challenges such as (i) the conservatism of traditional piledesign methods, (ii) the difficulties in sizing hammers for large diameter(&gt;4 m) monopiles and predicting pile driveability, (iii) the difficulty inpredicting set-up effects and the long term capacity of offshore platforms,(iv) the impact of cyclic loading on foundation resistance, and considerationsfor short grouted connections on high diameter/thickness ratio piles. Considering the array of issues facing the industry, this paper also identifiespossible areas of future research that could lead to improved industry practiceand better efficiency.

Introduction

Designing marine and offshore structures is a complex process with manyinterfaces between different engineering processes from structural designissues to fabrication and installation details. However, one of the greatestsources of uncertainty can be attributed to the geotechnical design of thesupporting foundations. Determining an appropriate soil reaction (both ultimatecapacity and stiffness) is complicated by the fact that soil is a naturallyoccurring, non-linear, anisotropic, non-homogenous material, which is bothnon-linear and viscous when loaded. As a result, offshore foundations are oftendesigned using a series of simplifying assumptions, which are based on pastexperience and empirical observations. The accuracy of these simplifyingempirical approaches varies in different foundation designs and can impact theconstructability as well as the underlying factors of safety and the accuracyof predicted stiffness and dynamic responses of the supported structures. It isclear that there is significant room for improvements in marine foundationdesign to ensure that there is a consistent reference for factors of safety andreliability across every offshore or marine structure, while adopting efficientengineering designs.