PROPEX Armormax HPTRM installed along the steep roadside slope adjacent to Highway 93.
Vegetation growing through the PROPEX Armormax system on the stabilized slope.
Vegetation established across the stabilized slope, with PROPEX Armormax anchor components visible at the surface.
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The City of Hampton used PROPEX® Armormax® to stabilize the Big Bethel Blueway drainage channel. The system showed no erosion after floodwater reached four to six feet during installation while supporting a vegetated approach to erosion control.
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Lost Trail Pass is located along the Idaho-Montana border, approximately 0.5 mi. (0.8 km.) west of the Continental Divide. Highway 93 provides a primary route through the mountainous area and to the summit.
A slope adjacent to the roadway was experiencing instability despite previously installed geogrid reinforcement. The Western Federal Lands Highway Division (WFLHD) needed a long-term stabilization solution that could reinforce the slope while supporting vegetation and complementing the surrounding environment. Due to the site’s remote location, the system also needed to be practical to transport and install.
The failing slope presented a potential risk to the structural stability of the adjacent roadway. The slope reached a maximum height of approximately 85 ft. (25.9 m.) and, at its steepest point, had a gradient of 0.75H:1V. Heavy winter snowfall added another design consideration, requiring the stabilization system to account for significant surface loading.
Solmax analyzed the slope conditions to determine an appropriate approach for surficial stabilization. The analysis included a snow load of 450 psf (21.5 kPa) to account for the winter conditions experienced at Lost Trail Pass. In addition to meeting the required stabilization performance, the selected system needed to accommodate the site’s limited access and allow construction to proceed without closing Highway 93.
Based on the geotechnical analysis, PROPEX® Armormax® Engineered Earth armoring System with B3 earth anchors was selected for the project. The system combines Engineered Earth Anchors™ with a High-Performance Turf Reinforcement Mat (HPTRM) to provide erosion control, surficial slope stabilization, and vegetated reinforcement. The system is designed to improve slope stability while providing long-term erosion protection for up to 75 years.
Approximately 600 ft. (183 m.) of slope, ranging from 35 ft. to 85 ft. (10.7 m to 25.9 m) in height, was stabilized with PROPEX Armormax. Installation took approximately one month, and Highway 93 remained open throughout construction. The system’s lightweight components also helped address constraints associated with transportation and installation in the remote mountain location.
Following installation, vegetation began establishing across the stabilized slope. At the time of the post-installation assessment, no instability or erosion was observed, providing the vegetated stabilization solution sought by WFLHD while maintaining roadway access throughout construction.