Guanella Pass Project, Georgetown to Grant, Colorado

FHWA Central Federal Lands Highway Division and Carter Burgess

Yeh and Associates provided engineering services for a series of projects for the Federal Highway Administration. One of the projects assigned to Yeh and Associates involves the widening and realigning several miles of highway that meander through steep mountainous terrain on Guanella Pass (Colorado Forest Highway 80). Guanella Pass is located within the Pike and Arapaho National Forests, beginning at US 285 in Grant and ending in Georgetown near Interstate 70. The existing roadway is a two-lane thoroughfare of various widths and many sharp switchbacks and is primarily used for recreation purposes. The road passes through forest, shrub land, and alpine tundra habitats.

Reconstruction and rehabilitation of the 23-mile long Guanella Pass Road consists of modifying the roadway to create a consistent width of 25 feet. Roadway improvements utilizing combinations of asphalt with chip seal and gravel portions. Due to the topography of the study area, most of the new alignment was designed with both cut and fill earth retaining structures. The geology of the project area is complex with numerous fault features and complicated groundwater conditions. Environmental concerns were a major issue throughout this project due to the sensitive alpine ecosystem, numerous wetlands, and recreational use of the area. Yeh and Associates worked closely with the U.S. Forest Service to ensure that impacts during the geotechnical investigation drilling program were minimized.

Design elements included slope grading, retaining wall designs, rock slope stability recommendations, soil erosion mitigation alternatives, and pavement design. As part of our investigations for cut and fill slope stabilization, both conventional and difficult-access drilling were utilized. Difficult-access drilling was placed by crane in remote access areas. This was done to minimize impact on the Forest Service lands and disruption of the traveling public.