An Innovative Case Study on the Use of Launched Nails for Landslide Repair

A record snowfall throughout the Rocky Mountains during the winter of 2010/2011 combined with torrential spring rainfall led to infrastructure damage throughout Montana, Wyoming, and North Dakota. Many roadways were closed due to flooding and landslides. Interstate 90 - between Hardin, MT and Buffalo, WY - experienced multiple deep-seated landslides and several shallow slips. One of the landslides occurred at MM 16.3 on the westbound on-ramp, a critical access point to I-90 due to the vicinity of the Wyoming Port of Entry. A 3-m to 4-m (10-ft to 12-ft) scarp near the guardrail led the Wyoming Department of Transportation (WYDOT) to look for innovative techniques to quickly stabilize the ramp to permit safe traffic flow. Safety and right-of-way concerns also complicated the design and construction of any earthwork structures. WYDOT chose launched (ballistic) soil nails faced with reinforced shotcrete to provide temporary stabilization of the near-vertical scarp. The temporary stabilization allowed for stability of the roadway platform and also permitted construction of a large earthen buttress. Due to the time and safety constraints involved, as well as the innovative technology selected, unique approaches in the slope stability modeling, onsite design, and construction planning were required.