Geotechnical Challenges in Reconstruction of Cottonwood Pass Road, Colorado: Fid-Bau Portal

Geotechnical Challenges in Reconstruction of Cottonwood Pass Road, Colorado

Arthurs, James M.

Cottonwood Pass Road in Gunnison and Chaffee Counties, Colorado, is a high elevation (summit at approximately 12,110 feet) mountain pass between Buena Vista on the east and Crested Butte on the west. It provides access to numerous recreation areas, and camping and picnic areas of the Gunnison and San Isabel National Forests. Due to insufficient roadway geometry, safety, and drainage, and heavy use by oversized recreational vehicles, a roadway improvement project was developed. Previous studies identified the potential for large-scale, deep-seated landslides west of the pass, and led to consideration of either an alternate major realignment of the road substantially impacting the environment; or use of several, relatively large fill-side retaining structures escalating the total project cost. However, the previous studies do not have consensus on the locations and extents of active moving landslides, and subsequent investigations determined no evidence of active deep-seated landslides impacting the roadway prism. Smaller scale slumps and shallow translational slides were identified and evaluated along high elevation sections of the route. This paper discusses the field evaluation and investigation, analysis, and mitigation methods employed for construction of the Cottonwood Pass Road. It also presents observations and insight from the reconstruction project.