GRI provided geotechnical services for the US 26 Glencoe Road project. Goals included replacing Glencoe Road bridge over US 26 with a new five-lane, two-span bridge; lengthening and widening the US 26 westbound exit ramp; replacing the culvert on Glencoe Road north of the interchange with a bridge structure; improving pedestrian and bicycle connections on the new bridge over US 26; constructing a path beneath the new bridge on Glencoe Road; and improving intersection components, such as traffic signals, signage, striping, drainage, and water quality. The new bridge over US 26 is approximately 260 feet long and 95 feet wide and supported by driven steel piles resistant to liquefaction. The east approximately half of the bridge was constructed in the location of the existing bridge. The exit and on-ramps and Glencoe Road north and south of US 26 were realigned, widened, and raised. Retaining walls with a maximum exposed height of up to 20 feet were constructed to retain new embankment fill and minimize encroachment into adjacent wetlands. Widening along the WB entrance ramp was made without retaining walls by steepening the slope to 1.5H:1V with an angular stone embankment. The retaining walls along the WB exit ramp and west side of Glencoe Road north of US 26 consist of mechanically stabilized earth (MSE) walls. The culvert beneath Glencoe Road was replaced with a new pile-supported bridge structure about 40 feet long and 85 feet wide that will allow for a pedestrian/bike path. The embankment beneath the bridge at each abutment is supported by a soil-nail wall with an exposed height of up to 20 feet below the pile caps. The field investigation included 29 drilled borings, nine hand-augers, and infiltration testing. Extensive analyses were conducted to identify and quantify the site-seismic response and related hazards, particularly the liquefaction potential and estimated settlements, slope instability risk, and pile downdrag loads as they related to the design of the project elements. GRI provided design and construction criteria for bridge pile foundations, MSE and soil-nail retaining walls, new embankments, excavation, shoring, dewatering, and subgrade stabilization. GRI personnel provided construction-phase engineering consultation and observation services to ODOT.

Location: North Plains, Oregon

Owner: Oregon Department of Transportation (ODOT)

Market Sector: Transportation 

Services: Geotechnical Engineering, Geologic Hazards, Seismic Engineering, Construction Services