Houston The Importance of Soil damping for Dynamic Offshore Geotechnical Problems with Special Consideration of Pipe-Soil Interaction

In dynamic soil-structure interaction problems soil damping is an important consideration for assessing both limit state and fatigue conditions as well as ground response for earthquake conditions. It is also, relative to the strength and stiffness characterization of the soil, less clearly understood by geotechnical engineers. Part of the challenge is that for soils the damping is derived from two sources. Radiation or geometric damping is frequency dependent as well as dependent on the geometry of the soil-structure system. The greater the likelihood of transmitting energy away from the foundation (or pipeline) the greater the damping. The second source of damping is material damping which depends on the soil non-linearity and is therefore dependent on the amplitude of the displacements. How these two sources of damping are combined is also challenging.

The webinar will present several examples demonstrating how damping levels are often underestimated. The examples will focus on field data, model test results and numerical simulations to evaluate damping levels. Observed field response of building under earthquakes, model test results of conductors and offshore steel jackets, and the ground response for a thick clay deposit will be presented. Finally results of numerical simulations of a pipe embedded at the seafloor and subjected to vertical excitation will be discussed. In this case the radiation and material damping components are independently identified and a combination rule proposed. The damping levels in these simulations were found to be much greater than damping values recommended in existing codes. These higher damping values can have a significant impact when evaluating fatigue life for pipelines subjected to slugging or for evaluating acceptable span lengths.

About the Presenter
Edward C. Clukey, Ph.D., P.E., F.ASCE, earned his masters and bachelors degrees from Worcester Polytechnic Institute and his doctorate from Cornell University. He is a registered professional engineer in California and Texas, a member of the Society of Underwater Technology and a Diplomate in ASCE for both Geotechnical and Ocean Engineering. For the past 45 years, Dr. Clukey has focused on offshore geotechnical engineering for the development of oil and gas reserves. His research at Cornell and in the early part of his professional career addressed problems on wave-seafloor interaction. He was Geotechnical Advisor at BP America (1998-2015) and worked on deepwater foundation, geotechnical aspects of pipelines and risers, as well as geotechnical aspects of earthquake and arctic engineering. Previously, he helped initiate the marine geotechnical program for the U. S. Geological Survey in California (1976-78) and prior to his BP experience worked for McClelland Engineers (1983-1985) and Exxon Production Research (1985-1998)). Since1991 he has been actively involved with the development of suction caisson technology for deepwater applications. This work resulted in over ten publications on the topic and the installation of over 100 suction caissons throughout the world for BP. He chairs the API task group which has developed industry guidelines for geotechnical aspects of conductors, risers and pipelines, now currently in both in API and ISO design documents. Throughout his career he has championed the use of centrifuge model testing and advanced numerical models to address complex offshore geotechnical technical issues, managing ten centrifuge programs for problems related to ice gouging of the seafloor, suction caisson technology, piles capacity in Angolan soils, conductor and SCR fatigue, and the seismic response of steel jacket structures and subsea manifolds. Since his retirement from BP he has become an active committee member in COPRI developing a standard practice for renewable energy as well as a member of the ASCE Geo-Institute developing guidelines for the risk and reliability of geotechnical structures and foundations. He is now a yearly lecturer at MIT and Cornell University and has a working relationship with the multi-disciplinary company, The Jukes Group. Dr. Clukey is the author of 55 technical publications and his experience covers many regions throughout the world.

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