December 20, 2001August 2, 2026

EXH AR053223: Effect of Shear Modulus on Deformations and Reinforcing Stresses of MSE Walls — Third Runway Project

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Memorandum dated December 20, 2001 from Michael Bailey, P.E. and Reda A. Mikhail, P.E. of Hart Crowser, Inc. to Jim Thomson, P.E. of HNTB Corporation regarding AR053223, project 4798-40. Analyzes sensitivity of MSE (Mechanically Stabilized Earth) wall design to variations in soil shear modulus under dynamic/seismic loading for the Third Runway Project at Sea-Tac Airport, North Safety Area (NSA), Section 105+20. Uses FLAC finite difference analysis program with Mohr-Coulomb constitutive model; compares G/Gmax ratios of 0.55 (stiff, site-specific ProShake/QUAD4 response analysis) and 0.28 (large strain, pressuremeter data per Bellotti et al. 1986) for fill soils. Reports lateral deformations and tensile stresses of metal strip reinforcing elements relative to AASHTO allowable stress (0.55 of yield strength). CC to John Sankey, P.E., RECo.

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As the source for federal transportation grants, the Puget Sound Regional Council was charged with developing a system to meet the growing need for commercial aviation. When the search for a second airport failed, they authorized the Port of Seattle to build the Third Runway, with a mandate to develop a noise abatement and mitigation program. In their effort to stop the Third Runway, the ACC argued over every detail of the Port's efforts--including property buyouts and sound insulation. The dispute was meant to be settled by a three member Expert Arbitration Panel. This is their final report. It finds 2-1, that the Port's program was insufficient in several respects. Despite that, funding for the Third Runway was approved by the PSRC, and the 'Port Package' program, proceeded largely unchanged. Expert Arbitration Panel's final decision finding that the Port of Seattle had not shown sufficient reduction in real on-the-ground noise impacts to satisfy noise reduction conditions required for approval of a third runway at Sea-Tac International Airport. The majority decision concluded the Port's noise abatement programs were insufficient despite being impressive in scope.

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