CASPER, Wyoming – A landslide along Interstate 90 west of Sheridan is scheduled to be repaired the week of Aug. 19. The work will require closing the right lane to eastbound traffic at mile marker 6.9 and reducing speeds to 45 mph.

According to the Wyoming Department of Transportation, the repair costs are estimated at $36 million. The contractor responsible for the project is GSI.

In early July, the WYDOT Commission approved $341,137 in emergency funding for District 4 to prevent a multi-year landslide that would potentially close a road, according to a news release. The mitigation measures were necessary to ensure the safety of drivers on I-90 until the State Transportation Improvement Program construction project planned for that section can be completed.

Landslides are common in Sheridan County when soils, usually clay soils, become oversaturated and lose their “stickiness” and give in to gravity. Most of these clay soils sit on a shale base and offer little to no resistance to which they can adhere. The soils become too heavy and follow the path of least resistance by falling off the slope, WYDOT said.

The landslide was first noticed by Sheridan maintenance personnel in May 2017 and reported to WYDOT geologists, who have been monitoring it ever since. Moisture and gravity have contributed to the dam’s movement in recent years, so the temporary railing installed in 2019 had succumbed to the erosion process, eliminating the right shoulder and now threatening to undermine the roadway.

Due to the violent new movement of this landslide, the lack of a road embankment, and the compromised temporary guardrail installation, county maintenance personnel determined that the landslide needed to be mitigated before the right lane was impacted.

GSI will use a soil nailing technique to secure the slope. Soil nailing is a structural remediation technique used to treat unstable natural earth slopes. It involves drilling holes into which steel rods are inserted into a slope face and then grouted in place. A mesh will be attached to the ends of the rods to hold the slope face in place, WYDOT said.

Prior to applying for emergency funding, construction plans were completed to mill, grade, and rebuild I-90 from the Montana state lane between mile markers 0 and 8. This project is scheduled to be bid and awarded in October 2024, with anticipated construction to begin in spring 2025. The project scope also includes relocating both eastbound lanes toward the median to avoid this and other potentially hazardous landslides between mile markers 3.88 and 8. The project also includes major repairs to two bridge structures and replacing four bridge structures with box culverts.

This project has been part of the State Transportation Improvement Program since 2018 and is estimated to cost $36 million.

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