CASPER, Wyo. — A slope failure along Interstate 90 west of Sheridan is set to be repaired the week of Aug. 19. The work will require the right lane for eastbound traffic to be closed near mile marker 6.9 with speeds reduced to 45 mph.
The repair will come at a cost of $341,137, according to the Wyoming Department of Transportation. The contractor in charge of the project is GSI.
In early July, the WYDOT Commission approved emergency funding for $341,137 to District Four to mitigate a potential road-closing slope failure that has been moving for several years, a news release states. The mitigation effort was needed to ensure the safety of drivers on I-90 until the State Transportation Improvement Program construction project scheduled for this section can be completed.
A common occurrence in Sheridan County, slope failures happen when the soils, commonly clay, become overly saturated and lose their “sticky” factor, giving way to gravitational pull. Most of these clays are sitting on a shale base, offering little to no resistance to adhere to. The soils become too heavy and follow the path of least resistance, falling away from the slope, WYDOT said.
The slope failure was first noticed in May 2017 by Sheridan maintenance staff and reported to WYDOT geologists, who have been monitoring it since. Moisture and gravity have aided in the embankment’s movement over the past few years, to the point that the temporary guardrail installed in 2019 had succumbed to the erosion process which eliminated the right shoulder and now threatens to undermine the travel way.
Due to the aggressive new movement of this slope failure, the lack of road embankment shoulder and compromised temporary guardrail installation, district maintenance staff determined the slide needed to be mitigated before the right lane of travel was compromised.
GSI, will use a soil nailing technique to secure the slope. Soil nailing is a remedial construction measure to treat unstable natural soil slopes. It involves drilling holes for steel bars to be inserted into a slope face and then grouting them in place. Mesh is attached to the bar ends to hold the slope face in position, WYDOT said.
Before the emergency funding request, construction plans were finalized to mill, level and overlay I-90 from the Montana state lane between mile markers 0 and 8. This project is scheduled to be let and awarded in October 2024, with an anticipated start date of spring 2025. The scope of the project also includes shifting both lanes of eastbound travel toward the median in order to avoid this and other potentially compromising landslides between mile markers 3.88 and 8. The project also includes major repairs on two bridge structures and replacement of four bridge structures with box culverts.
This project has been in the State Transportation Improvement Program since 2018 and is estimated to cost $36 million.
CORRECTION, Aug. 12, 2024: This story originally cited an incorrect cost for just the slope repair work. The story has been corrected.
