DIP Landslide - MP 32.5, Chief Joseph Highway (WY 296)

The DIP Landslide is located at MP 32.5 on the Chief Joseph Highway (WY 296) and is approximately 30 miles northwest of Cody, Wyoming. This section of WY 296 is a two-lane road with narrow shoulders that was constructed in 1995 and provides the only year-round access to the Sunlight Basin. The slide is currently affecting the entire roadway width for 180 feet, with slide movement occurring at the projected depth of approximately 25 feet below the roadway centerline.


WYDOT Maintenance first noted minor pavement cracking and settlement at the site in 2015.  In the spring of 2017, arcuate cracks developed in the pavement out to the centerline and some minor downslope movement deformed the westbound lane. This prompted the initial geotechnical investigation of the DIP Slide in October 2017. The site remained quasi-stable and under observation during 2018. Further slide movement, in the spring of 2019, caused expansion of the pavement cracks and significant deformation of both lanes. The main scarp in the pavement measured 1.5 inches wide and displayed 3 inches of vertical movement in the influenced area. The accelerated damage from the spring of 2019, necessitated an expedited design to mitigate the DIP Slide, and Yeh & Associates Inc. from Denver, Colorado was contracted on July 3, 2019, to complete the mitigation design for this site.


The final design utilized Coupled Shear Piles (CSP) to stabilize the highway. The CSP design concept utilizes the frame action of drilled shafts that are connected with a rigid pile cap to more efficiently resist both shear and moment induced by lateral movements of the landslide. This design approach is similar to the design on previous WYDOT projects including the Narrows Landslide project (N212112), Hoback North Landslide project (N104087), and Bear River Landslide project (N104066).


The contractor started work on June 25, 2020, by constructing a one-lane detour, and the first of the 39-inch diameter, 70 foot deep drilled shafts were installed on July 15, 2020. The final drilled shaft (#120) was completed on September 11, 2020, while the final section of the cap, tying all the drilled shafts together, was poured on October 31, 2020. The highway was opened to two-way traffic on a temporary pavement on November 15, 2020.