Emergency slide repair work to be completed on Interstate 90 east of the state line

Sheridan, WYO -  The Wyoming Department of Transportation and its contractor GSI will begin collaborative work on an emergency slide repair west of Sheridan.

In early July, The Wyoming Department of Transportation 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. This mitigation effort was needed to ensure mobility on Interstate 90 remains intact until the STIP construction project scheduled for this section can be completed.

A common occurrence in Sheridan County, a slope failure happens when the soils, commonly clay, become overly saturated and lose their ‘sticky’ factor, and give way to gravitational pull. Most of these clays are sitting on a shale base, offering little to no resistance for the clay to adhere to. The soils become too heavy and follow the path of least resistance and fall away from the slope.

This particular slope failure is located on the eastbound lane of I-90 near mile marker 6.9.  This slope failure was first noticed in May of 2017 by Sheridan maintenance staff and reported to WYDOT Geologists who have been monitoring it since. Moisture and gravity have aided in the embankments 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 roadway 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.

WYDOT’s contractor, GSI will utilize 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 which are then grouted in place. Mesh is attached to the bar ends to hold the slope face in position.

GSI is scheduled to begin work the week of August 19 and will require WYDOT to temporarily close the right travel lane to motorists. Traffic control will include the closure of the eastbound, right travel lane near mile marker 6.9, and the speed limit will be reduced to 45 mph.

Before the emergency funding request, construction plans were finalized to mill, level, and overlay I-90 from the Montana State lane from mile marker 0 to 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 from mile marker 3.88 to 8.00.  The project also includes major repairs on two bridge structures and replacing four bridge structures with box culverts.

This project has been in the State Transportation Improvement Program (STIP) since 2018 and is estimated to cost $36 million.