Seismic Site Response for an LNG Facility—Analyses and Lessons Learned

A permitting-level design was conducted for a liquefied natural gas (LNG) facility, proposed on the northwest Oregon coast. The permitting-level design required the structure to operate safely during the design level ground shaking from an earthquake on the underlying Cascadia Subduction Zone interface fault. The site is underlain by 350 feet (107 meters) of predominantly soft non-plastic silt and medium-dense to dense sand layers. The design of the LNG facility, as well as the foundation system, required an estimation of the liquefaction potential and cyclic performance of the silt and sand soil layers, however, there is limited published information for evaluating the cyclic behavior of deep soil deposits. This paper summarizes the results of (a) an extensive site investigation and cyclic soil laboratory testing conducted to develop cyclic parameters and (b) nonlinear effective-stress site-response analyses using the computer program D-MOD2000. The analyses were conducted to evaluate the cyclic performance of the soil layers for use in designing the foundation system. The results of the cyclic testing and lessons learned during the numerical modeling are presented.