Ninth OTRC Honors Lecture: Geotechnical Contributions to Offshore Development

Abstract The paper makes a review of important contributions from the geotechnical profession to offshore development, from the early piled and gravity base foundations to the new lightweight skirted foundation concepts. Geotechnical breakthroughs have enabled new and daring constructions offshore and opened the way to cost-effective solutions. At the same time, the requirements and conditions imposed by the offshore industry also greatly contributed to an improved understanding of the behavior of soils under new loading conditions. The paper looks into the development of enhanced site investigations and soil characterization, model testing, improved design methods and new foundation solutions. Joint-industry sponsored research proves to be a necessary contributor for developing new, safer and more cost-effective solutions. The paper outlines the challenges facing the profession when entering the new millennium and the steps needed to meet these challenges. Introduction The OTRC Honors Lecture series covers a wide array of contributions from different fields of offshore engineering. Bramlette McClelland's overview in 1991 on the frontiers in geotechnical engineering, Ben Gerwick's research promises for concrete sturctures and Don Murff's position paper on the use of centrifuge were the predecessors of the present paper. Odd Faltinsen on sea loads on floating systems and Leon Borgman on directional wave polyspectra presented views from hydrodynamics. Patrick Dunne and Mamdouh Salama outlined the structural challenges and innovations associated with resource exploitation in deep water, and Allin Cornell reported on the contributions of structural reliability to offshore engineering. This paper gives a personal view of major geotechnical achievements that have contributed to the progress of the offshore industry. The ideas presented are favorably biased towards geotechnics. The author is of the opinion that geotechnical progress has enabled the offshore industry to move towards increasingly optimum solutions. Perhaps these contributions do not receive today the recognition they deserve. On the other hand, the needs and requirements of the offshore industry have contributed significantly to the advancement of geotechnical knowledge and this should also be recognized. Achievements and Challenges Over the past 25 years, geotechnical practice has greatly evolved and improved, at times with giant leaps, because of the needs of the offshore industry. The following takes a brief look at the progress made in site investigations, testing for soil characterization and evaluation of soil models, improved foundation design methods and the development of new foundation solutions. The OTRC session presents companion papers on specific achievements within seismics, skirted foundations, pile design and seafloor instability. This overview mentions the main areas where significant advances have been made, and where needs are judged to be the greatest. The reader should consult the other papers for specific recent advances. Site and Soil Investigations. For adequate design of foundations, soil parameters need to be determined through a combination of interpretation of the local geology, in situ testing and laboratory testing. The impetus of offshore work had led to rapid developments in both in situ and laboratory testing. Equipment, testing methods, methods of interpretation and parameter determination are some of the aspects that have greatly benefited from enhanced research and attention. In Situ Testing. In particular, the developments around the piezocone penetration test and new sampling devices to be used at increasingly greater depths have been noteworthy