Landslide Segment on Highway 26

US-26/287 is the most direct route for accessing the Grand Teton National Park from central and southeastern Wyoming. Locally it is referred to as the Togwotee Trail, named after the Togwotee Pass, which is at an approximate elevation of 9,700 feet, and is part of the Centennial Scenic Byway. The highway was originally built between 1955 and 1967 by the U.S. Bureau of Public Roads with various repairs and upgrades occurring periodically since that time.

In 2005 Wyoming Department of Transportation (WYDOT) identified a 21-mile segment along the roadway between Moran Junction and Dubois that was in need of major roadway improvements. Approximately 20 landslides were also observed within the outlined segment. WYDOT conducted subsurface investigations and designed roadway improvement measures that were to be constructed from 2006 through 2010.

Landslide Technology (LT) was retained to assist with geologic reconnaissance and interpretations, evaluate landslide features, review potential slope instability, and develop conceptual-level landslide mitigation measures. Recommendations were provided for additional field explorations, geotechnical instrumentation, and monitoring at selected sites along the alignment. The additional explorations and instrumentation allowed LT and WYDOT to refine the geologic interpretations for slope stability modeling input. LT completed initial stability analyses to evaluate potential mitigation measures that included: toe berms, shear keys, rock inlays, trench drains, retaining wall structures, lightweight fills, and horizontal drain arrays. Preliminary cost estimates were prepared for construction of each alternative.

Once WYDOT selected landslide mitigation measures for each slide, LT prepared recommendations for final designs, technical specifications, and engineer’s estimates. LT has also been retained to train WYDOT inspectors and provide part-time construction observation of landslide repairs including horizontal drains, shear keys, buttresses, EPS (Geofoam) fills, and post-tensioned ground anchors.