Notes
GeoSyntec Consultants letter dated 2 March 2001 to U.S. Army Corps of Engineers (Jonathan Freedman) and Washington State Department of Ecology (Ann Kenny) correcting an error in Comment #7 of their 16 February 2001 technical review letter submitted on behalf of the Airport Communities Coalition (ACC) regarding the Third Runway project at Seattle-Tacoma International Airport. The correction changes ‘underestimate’ to ‘overestimate’: the Hart Crowser methodology, which calculated yield acceleration only for the failure surface with the lowest static factor of safety rather than systematically searching for the failure surface with the lowest yield acceleration, may seriously overestimate the seismic resistance of the wall. The attached revised Comment #7 argues that proper pseudo-static slope stability analysis must independently search for the critical seismic failure surface, examine sliding block failure surfaces along weak peat layers and liquefied sand deposits, and that the area of ground improvement may need to extend further back into the embankment. Signed by Patrick C. Lucia and Edward Kavazanjian Jr., Ph.D., P.E., G.E. AR021820–AR021822.