DFI Contribution to OTC 2012, OTC 2013 and Beyond… by liquefaction is clearly visible in the aftermath of earthquakes, and is also a signi- ficant concern for offshore design of pipe- lines and shallow foundations. Travasarou introduced a framework for identifying liquefaction hazards, quantifying the risk and the impact of the liquefaction and pro- posing mitigating solutions where necessary, and described an extensive case history. In another paper, Stevens described a Pictured left to right: Philippe Jeanjean – moderator, Bob Stevens, Gerry Houlahan, Dongdong Chang, Thaleia Travasarou, Paul Doherty The annual Offshore Technology Conference (OTC), held in Houston every May, is the premier event for practitioners in the offshore engineering and marine technology fields. One critical topic of interest for this community is the area of marine foundations and offshore soil- structure interaction. In light of this, DFI’s Marine Foundations Committee developed a technical session at OTC 2012, titled “Geotechnical Technology Transfer from Onshore and Near-Shore Practices.” The session was deemed a success, drawing about 150 people to hear the six technical speakers. The first was Paul Doherty from GDG Ltd., who presented a paper, co-authored by Gerry Houlahan (Moffatt & Nichol) and Robert Stevens (Fugro), about the technical challenges facing the marine foundation sector and the evolution of industry design tools. Existing uncertainties and limitations in the traditional standards for offshore pile design were discussed and suggestions given for further research. (See page 51 for a condensed version.) The second presen- tation was delivered by Dongdong Chang from Arup who addressed the seismic analysis of soil-pile-structure interaction for the foundation design of LNG tanks. Advantages of more recently developed design tools were demonstrated by com- paring (i) a simplified substructure method and (ii) a direct non-linear finite element solution for the dynamic analysis of the tank and soil support. The direct method was shown to provide more reasonable results across a range of conditions and was deemed preferential in cases where the soil response was highly non-linear and inertial effects were significant. The next presentation was delivered by the DFI Marine Foundations Committee Chair, Houlahan, who stood in for the authors (Mario Lenzi, ACMAR, and Paola Campana, Studio Campana of Italy), who could not attend. Houlahan eloquently introduced the subject of underwater ground anchors, covering the initial design of the anchoring system, the theoretical behavior, the field installation performance and the compari- son of experimental results with analytical models. Highlighted was the complex inter- actions between contractors, designers, engineers and fabricators that resulted in the anchoring system that stabilized the Quay wall at Ravenna Port, allowing the port to be dredged to accommodate larger vessels. The fourth presentation was by Thaleia Travasarou from Fugro, who described the impact of liquefaction on buried structures. This topic is prominent in onshore geotechnics where the devastation caused challenging pile design and installation at Escambia Bay in Florida. At this site, square precast, prestressed piles were installed using a Delmag single acting diesel hammer. The piles underwent significantly harder driving than anticipated and showed a particularly high rebound, with corresponding high quake in CAPWAP analysis. However under static load tests the piles demon- strated uncharacteristically low failure loads. This behavior was attributed to the angular nature of the sand grains. The final presen- tation by Dr. I Thusyanthan of Cape Group Pte Ltd. dealt with the behavioral classifi- cation of soils for design of subsea pipelines. Limitations of different standards and the implications for the practical design of seabed ploughing in various soil types were discussed. The session highlighted an extensive range of challenges, but also outlined the detailed set of tools now available to geo- technical engineers to analyse these complex problems. When combined with an appro- priate level of experience, we can signifi- cantly “de-risk” complex projects. A critical component for success is the accurate calibration of the more complex design tools, which insures the sophisticated tools are being wielded in the correct fashion. OTC 2013 – May 6-9 at Reliant Park, Houston, Texas: Call for Papers Considering the success of this year’s technical session and the general interest in offshore and marine foundations, the Marine Foundations Committee would like to continue the session on “Geotechnical Technology Transfer from Onshore and Near-Shore Practices” in 2013. We hope this technical session will become an annual OTC event and will become a focal point of the marine foundation calendar. With this in mind, the Marine Foundations Committee is currently soliciting expressions of interest from individuals in preparing a paper for the event and delivering a presentation. Interested parties should contact DFI head- quarters at [email protected] by July 15 with a brief proposal describing their area of interest and the subject of the proposed paper for review by the committee. The current OTC timeline for the submission process is August 20, 2012 for formal abstracts and January 8, 2013 for papers. DEEP FOUNDATIONS • JULY/AUG 2012• 27
