Slope Stability

Beartooth Pass Highway: Montana Dept. of Transportation

In May 2005, the famous Beartooth Highway, gateway from Montana to Yellowstone Park, was heavily damaged by debris flows. Within a few days, emergency repair was funded by Congress. WAI geologists and engineers were involved in all aspects of the project from initial description to construction monitoring. Specifically, we mapped bedrock characteristics in preparation for blasting; mapped the flows; supervised geotechnical exploration; and performed stability analyses for repairs. WAI prepared the quantitative risk assessment that helped justify installation of massive debris flow fences. The design-build team mobilized Kiewit and JTL for construction, HKM for civil design, and Shannon & Wilson and WAI for geotechnical services. The project was estimated at $20 million and built for $12 million. The reconstruction was completed ahead of schedule and the road was reopened in October 2005. The project has received three major national awards for projects in its class.

ASARCO Tacoma Superfund Restoration

The ASARCO Superfund site, located along the shoreline of Commencement Bay in Tacoma, Washington, is the former site of a copper and lead smelter. WAI has been involved in the project since 1987, working as a subcontractor to Hydrometrics and directly for ASARCO. The project involved extensive subsurface exploration, including drilling, shear wave measurements, and cone penetration tests. Seismicity and liquefaction assessments were prepared. The seismic assessment underwent a test run during the 2002 Olympia Earthquake, which triggered failure of loose hydraulic fills along the shoreline, in an area where liquefaction had been predicted. When the onsite containment facility was built, ground improvement was required, including dynamic deep compaction and vertical wick drains. WAI provided supervision and design services for installation of the double composite liner system, leak detection and collection systems, and final cap. We are currently the geotechnical engineers for post-reclamation development of prime residential and commercial real estate. Stack Hill, so called because a smoke stack almost 600 feet high stood at the site until recently, is bordered by steep gullies where landslides have destroyed homes. WAI provided stability analysis to determine setbacks and slope stabilization measures.

Grouse Creek Mine, Idaho

The tailings impoundment and waste rock repository were built on large landslides in the headwaters of the Yankee Fork of the Salmon River. The tailings dam embankment is nearly 400 feet tall and the waste rock repository comprises 50 million tons. As a subcontractor to Golder Associates, WAI used very deep test pits (up to 175 feet) and numerous borings and slope inclinometers to characterize the shear zones along the bottom of the slides. WAI supervised installation of shear keys to stabilize the slides.

Private Home on Bluff Above Snake River

This home is located adjacent to a steep bluff about 120 feet high that drops down to the Snake River in Jackson Hole. In order to take maximum advantage of the site’s aesthetics, the home was positioned within 30’ of the bluff. The Snake River has undercut the slope, causing slope failures that propagate upslope over time. WAI recommended helical piers to provide support for the foundation and micropile slope reinforcement

Dinosaur National Monument

Harper’s Corner Drive is the main access into Dinosaur National Monument. The road was built on a landslide that has moved about 20 feet since 1958 (about 5 inches/year). WAI’s field investigation consisted of piezometers to measure pore water pressure in the slip zone and slope inclinometers to measure landslide movement and locate the depth of the failure plane. The landslide is moving on weak bentonitic layers of the Mancos Shale, in response to elevated pore water pressures at the slip zone and undercutting by a stream below the toe. WAI recommended two options for remediation: a shear key to interrupt the failure surface or post-tensioned tiebacks.

Hirsch Project Birch Creek, Montana

This upscale home is situated on a recently active landslide. WAI analyzed the slide movement and supervised installation of large diameter drilled piers. The landslide has dammed the creek, creating a lake that was carefully enlarged after analysis of slope stability effects.