TagMechanically Stabilized Earth(5)

This engineering cross-section diagram from Sea-Tac International Airport illustrates the dramatic 179-foot elevation drop adjacent to the proposed Third Runway, showing how a massive retaining wall and new embankment would be constructed alongside Miller Creek. The exhibit depicts key infrastructure features including a permanent chain-link security fence, rock underdrain, silt fence, inner collection swale, and a minimum 50-foot creek buffer zone designed to protect the existing waterway. The drawing is part of the Miller Creek Instream and Buffer Enhancements project documentation associated with the Third Runway expansion.

This engineering study describes the design and construction of a 46-meter (150-foot) tall mechanically stabilized earth (MSE) retaining wall built along the western edge of Seattle-Tacoma International Airport's third runway embankment, believed to be the tallest such wall in the western hemisphere at the time. The wall was necessary to raise the ground level by up to 50 meters while avoiding encroachment into nearby wetlands and creeks. Monitoring of the wall during and after construction confirmed it performed safely and largely as predicted.

In February 2001, engineering firm GeoSyntec Consultants submitted a technical review letter on behalf of the Airport Communities Coalition, raising serious concerns about the proposed Third Runway expansion at Seattle-Tacoma International Airport. The review identified significant deficiencies in the geotechnical investigation and analysis supporting construction of the embankment fill and West MSE Wall, including insufficient soil strength data and inadequate seismic safety assessments. GeoSyntec warned that the proposed design — which would result in the world's tallest MSE wall built over weak, potentially unstable soils in a seismically active region — could fail under earthquake conditions, threatening both airport operations and nearby natural resources.