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In order to improve the safety of ships navigating the Savannah River along Elba Island and increase storage capacity of liquefied natural gas, Southern LNG designed an expansion of their facility that involved a one million barrel liquefied natural gas storage tank and containment dikes, process facilities, and a new slip dock. WPC was selected to perform the Geotechnical Engineering for the project.
WPC’s geotechnical and seismic study set new records for geotechnical work in the Savannah area in terms of boring depth, use of new technologies in field exploration, and laboratory testing and intensity of foundation and ground improvement evaluation. The field exploration program was comprised of soil test borings to 380 feet, cone penetration test (CPT) soundings and dilatometer test (DMT) soundings, in-situ pore pressure dissipation tests, and downhole seismic soundings to measure shear wave velocities. The laboratory testing included conventional soil index and classification tests, consolidation and triaxial strength tests, and advanced resonant column tests and dynamic triaxial tests to characterize soil properties under dynamic loading. WPC evaluated various foundation and ground improvement alternatives for the proposed tank, process facilities, and slip dock and developed construction recommendations for the dikes. Driven prestressed concrete piles were recommended for the tank and dock and preconsolidation with wick drains were recommended for the containment dikes.
The seismic hazard study involved identification and characterization of regional seismic sources, analysis of historical seismicity and development of site specific ground motions. The liquefaction analysis was performed in great detail using data from the standard penetration test borings, cone penetration test soundings and shear wave velocities. WPC evaluated various liquefaction mitigation techniques and the effect of liquefaction to pile foundations and slope stability.
WPC performed a design-stage pile test program for the Southern LNG Elba Island Terminal Expansion project. The purposes of the pile test program were to study the densification effect of the pile driving and to re-evaluate the liquefaction potential after pile driving; to test the axial pile capacity for the determination of the design pile length; and to test the lateral behavior of the piles, particularly the pile behavior under cyclic lateral loads.
The new design based on the pile test program saved the owner over $1 million in foundation construction costs. WPC developed detailed pile installation recommendations to help the bidding and construction of pile foundations. WPC began pile load testing on the next phase of the Elba Island LNG in the fall of 2006. This expansion will include two tanks that are larger than one million barrel tank installed in the earlier phase.
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