Section 10C, the northernmost portion of the Interstate MAX light-rail project, was completed under a design-build contract between FE Ward and TriMet. David Evans and Associates, Inc., was the design engineer of record, and GRI was the geotechnical engineer of record. The 1.5-mile-long alignment includes a 4,000-ft bridge to support the twin tracks. The alignment is typically underlain by soft, compressible floodplain soils that are up to more than 100 ft thick. GRI reviewed existing geotechnical information for the project, completed subsurface explorations and laboratory testing, and worked closely with the project team to address foundation support, abutments and fills, surcharge fill requirements, seismic design, liquefaction, downdrag considerations due to long-term secondary compression, retaining structures, railbed support, and pavement design. Foundation support for the two abutments and 27 bents for the bridge was provided by driven steel pipe piles and drilled piers. Three bents are supported by 7- and 8-ft-diameter drilled piers that range up to 90 ft deep. Most of the piles included measures to mitigate downdrag loads induced by the long-term settlement of existing and new fills. Construction of the project is complete. GRI personnel provided field engineering and construction observation services during foundation construction and rail bed and pavement subgrade preparation.
(Top photograph by Radcliffe Dacanay)