EMERGENCY RESPONSE AT KING COUNTY INTERNATIONAL AIRPORT/BOEING FIELD FOLLOWING NISQUALLY EARTHQUAKE

The magnitude 6.8 Nisqually earthquake shook the Puget Sound region on February 28, 2001. One of the locations with the greatest recorded ground acceleration was the Duwamish River valley in south Seattle near King County International Airport (Boeing Field). Facilities in the Duwamish River valley, including the airport, were constructed on fill soil placed on the estuary tide flats, and meander channels during the late nineteenth and early twentieth century. King County closed the Airport due to earthquake-related damage (caused by ground shaking and liquefaction of the underlying fill/native soil) to runways, taxiways, access ways, and concourses. The Airport closure resulted in a regional business revenue loss estimated at $4 million per day. Accordingly, repairing the runways to return airport to operation were given high priority. Earthquake-related effects at the airport included pavement cracking, vertical and horizontal offset between pavement panels, sand boils, ejection of large debris, and areas of soil loss in the vicinity of storm drain systems. Investigations using ground penetrating radar (GPR) showed no significant voids beneath the runway pavement and taxiways in areas where sand boils formed. Investigations also indicated local subsidence of the runway pavements, a general relationship between sand boil activity and former river meanders, and the presence of an older, undocumented concrete runway below portions of the existing main runway. The geotechnical engineering response included temporary subgrade stabilization using compaction grouting to support heavy wheel loads associated with landing of large, commercial jet aircraft. Geotechnical engineering recommendations were used by the Airport’s team of engineers and construction contractors to implement a repair program, returning the Airport to full operation by March 15, 2001, 15 days after the earthquake occurred.