Rebuilding a Highway Destroyed by the Oso Landslide

This project was one of the fastest design-build deliveries in Washington state history, reopening approximately one mile of a critical highway exactly six months to the day after the catastrophic landslide near Oso, Washington, on March 22, 2014. The landslide flowed thousands of feet across the Stillaguamish River valley, obliterating dozens of homes and spreading 10 million cubic yards of mud, trees and debris over a half-mile area. The slide buried approximately one mile of Washington State Route (SR) 530—a critical highway that connects a string of rural communities—with up to 20 feet of debris, closing it for four months.

It was against this backdrop that GeoEngineers, as part of Atkinson Construction’s SR 530 Emergency Roadway Reconstruction design-build team, began working with the Washington State Department of Transportation and local stakeholders to rebuild the roadway and deliver much-needed resources and hope to the area.

Approach

The volume and scale of slide deposits—including material in the project area from previous slides—appeared to limit the options for rebuilding the roadway. GeoEngineers’ geotechnical design solutions, including using base reinforcement for slope stabilization, installing a drain system in the slide area and using pavement reinforcement to control settlement, enabled contractor to construct portions of the new road over soft, unstable landslide deposits.

In addition to destroying large portions of the roadway, the massive slide completely disrupted the Stillaguamish River and its tributaries in the project zone. Many of these tributaries cross SR 530 and provide critical salmon habitat—a key concern for county and tribal stakeholders during the rebuilding process. GeoEngineers’ river specialists worked closely with the design-build team to develop a design that used five aluminized-steel, fish-friendly culverts rather than concrete boxes, thereby reducing costs, increasing speed of delivery and minimizing the need for additional wing walls, support structures and excavation.

Results

The Washington State Department of Transportation faced the daunting task of rebuilding the roadway and reconnecting the affected communities under some of the most difficult conditions the agency had ever faced. GeoEngineers and the design-build team helped the agency manage these conditions, save more than $5 million over its projected cost and reopen the new roadway exactly six months to the day of the slide—one of the fastest design-build deliveries in state history.