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EXH 384: Email Beaver to Bailey — 3R Embankment Subgrade Improvement Zones HC Rational

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Sea-Tac Airport
Third Runway
PCHB
Box 09

This internal engineering memo from Jamie Beaver to Mike Bailey, dated March 9, 2001, outlines the process used to determine subgrade improvement zones for a 3R embankment stability project. The analysis focused on liquefaction risks, using post-liquefaction undrained residual shear strength (PLURSS) values derived from seismic reanalysis, ultimately recommending improvement zone widths of 100–120 feet depending on location. The memo notes that factors of safety for the liquefaction and pseudo-static cases generally ranged from 1.0 to 1.2 across various zones.

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Notes

Exhibit 384 (AR 021697), dated 3/9/01, is an internal email from Jamie Beaver to Mike Bailey documenting the analytical process used to define embankment subgrade improvement zones for the Third Runway (3R) project at Sea-Tac Airport. The email details liquefaction triggering reanalysis using PSHA/ProShake PGA values, post-liquefaction undrained residual shear strength (PLURSS), composite shear strength approach, CPT input, NSA (North Satellite Area), factor-of-safety calculations (FS 1.1–1.2), subgrade improvement widths of 100–120 feet, pseudostatic and steady-state analyses, and discussions with Bob Maruska and HNTB. References west wall, station 156th, station 189+57, station 205+00, clay phi 30/32 degrees, and 1.8H:1V slope. Notation on document reads ‘REMOVE FROM FILE unless approved by Bailey.’

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