Following a major landslide triggered by heavy rainfall, Skagit County closed a section of Prevedal Road and established a temporary bypass in Washington state. Terraphase was retained on an emergency basis and mobilized to the site the morning after the initial phone call. The project required immediate geotechnical evaluation and stabilization design to restore access before the next wet season. The repair effort was jointly funded by the City of Lyman and Washington State Department of Transportation.
Scope of Services
Terraphase provided geotechnical consulting throughout the 30-, 90-, and 100-percent design phases to characterize the landslide and site conditions, identified factors that likely contributed to the slide, and presented potential stabilization and road repair solutions. Our team mapped the slide area and identified the root causes of the slope failure, which were the steep native slope, prior placement of uncontrolled fill to build the roadway, and poor existing surface drainage.
Notable Accomplishments
- Rapid emergency response with next-day on-site mobilization
- Full geotechnical support through all design phases
- Designed a reinforced soil wall solution tailored to site constraints
- Delivered a cost-effective, constructible design that enabled timely road restoration
