Beartooth Pass Debris Flows
Red Lodge, Montana
The Beartooth Highway is located south of Red Lodge, Montana and connects the City of Red Lodge to Cooke City, Wyoming. The highway is an important tourist route connecting eastern Montana to the northeastern entrance to Yellowstone National Park. The highway climbs a northwest-facing mountain range via several switchbacks to reach a broad plateau pass near elevation 11,000 feet.
Early spring rains on an abnormally deep snow pack resulted in extremely high volumes of surface water runoff. The runoff overwhelmed the drainage system and excess water sheet-flowed across the roadway and down the mountain in two natural drainages.
The water flow initiated debris flows that caused major damage at 13 locations along the highway. Damage generally consisted of large deposits of debris flow material on and upslope of the roadway and severe erosion and undermining down slope of the road. In many cases, debris flow chutes were scoured down to bedrock leaving a deep channel for the roadway to span.
Landslide Technology (LT) was retained by Montana Department of Transportation (MDT) to complete an emergency reconnaissance of the site. Teams of geologists and engineers performed an air reconnaissance of each site with a helicopter and completed detailed reconnaissances on foot. Conceptual design recommendations were prepared for each site assuming that MDT and LT would work together to prepare construction drawings and specifications in a joint effort. Conceptual mitigation options included a large rock cut to realign a portion of the road, rockfill embankments in some damage areas, MSE walls in other damage areas, and debris flow and rockfall fences to mitigate upslope hazards. To speed construction delivery, MDT management elected to let the project to a design-build contractor. LT's concepts report was provided to prospective design-build contractors to serve as a basis of design.
LT mobilized an engineer to work alongside design-build engineers reviewing design development and providing feedback to speed the design review process. Our onsite engineer observed geotechnical portions of the construction to verify that geotechnical concerns were adequately addressed during construction. The engineer provided regular updates to MDT and LT engineers in the home office to promote timely responses to contractor submittals. The project was completed ahead of MDT's target schedule.