Federal Way Link Extension - Deep Soil Liquefaction-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the design and construction of Structure C, a transit bridge on Sound Transit’s Federal Way Link Extension in Washington. The 7.8-mile, design-build project extends light rail from Angle Lake toward downtown Federal Way and includes three new stations.<br /><br />Structure C occupies a constrained site beside southbound I-5, with difficult access, wetlands, limited right of way, and an unstable slope. New geotechnical information revealed liquefiable soils and a lateral flow zone, raising permitting and construction risks. The reference-design piers could not adequately resist landslide forces, so the team assessed 11 alternatives, including ground improvement, soil replacement, stronger foundations, and longer spans.<br /><br />The selected solution uses strong piers with bearings that allow them to move independently of the superstructure, together with post-tensioned, spliced girders. A three-span, cast-in-place segmental balanced-cantilever bridge (300-foot back spans and a 500-foot main span) clears the flow zone and future fish passage. Top-down construction helped avoid disturbing the slope.<br /><br />Construction required close integration of design and field teams. Detailed erection planning, integrated 3D models and shop drawings, and extensive temporary works supported segment-by-segment construction. The team also managed access and shoring, precise geometry through 248 survey phases, concrete mix trials, thermal control, post-tensioning, and closure operations. The project illustrates how geotechnical discoveries and construction constraints can drive major design changes and demand coordinated planning.

Keywords

Structure C

Federal Way Link Extension

Sound Transit

transit bridge

design-build project

geotechnical risks

liquefiable soils

balanced-cantilever bridge

post-tensioned girders

top-down construction