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500-kV Transmission Line

500-kV Transmission Line
Southern Oregon

This 500-kV transmission line is approximately 60 miles long and extends from the Spencer Switching Station near Eugene to the Dixonville substation near Roseburg. Support for the new line is provided by nearly 300 settlement-sensitive steel-lattice towers on 3-, 4-, and 5-ft-diameter drilled piers ranging from 12 to 30 ft in length. The alignment is served by over 100 miles of temporary and permanent access roads. The first phase of the geotechnical investigation included a detailed reconnaissance to describe near-surface soil/rock and delineate areas of potential geologic hazards that could affect the design, construction, or performance of the transmission line. The field reconnaissance was followed by a detailed subsurface investigation along the alignment. A comprehensive laboratory testing program included routine classification tests and more-sophisticated testing to determine the engineering characteristics of the soils. GRI provided recommendations for road construction and foundation design, including spread footings and drilled piers, and conducted a full-scale pier load test. GRI developed construction drawings and specifications for five different foundation types. GRI also provided preliminary guidelines for earthwork and grading at the Dixonville substation. GRI personnel observed the construction of tower foundations on a full-time basis during the summer of 1991 and provided field engineering services during the 1992 construction season.

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