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January 23, 2017
Project: Hawthorne Avenue from Walnut to Crestview
Client: City of Colville
The city of Colville is the county seat of Stevens County in northeastern Washington. Its 4,700 residents work predominantly in agriculture, timber and mining. They also are committed to making their community safe, accessible and more livable.
Hawthorne Avenue crosses the city from east to west, connecting schools, churches, a city park and many residences, but the deteriorated street was very wide and difficult to cross. Its on-street parking was rarely used, and there were no pedestrian or bicycle facilities, nor was the street ADA-compatible due to uneven surfaces and connections with driveways.
In 2013, Welch Comer Engineers helped the city develop the Hawthorne Avenue Strategic Plan, which included utility coordination, conceptual roadway designs, estimated costs, public involvement and a strategy for funding. The plan recommended two new strategies: a road diet and the “complete streets” ethic.
The road diet modifies an existing public right-of-way from one that gives full priority to motor vehicles to one that is designed for all users, including pedestrians and bicyclists. The complete streets ethic is used to evaluate the best use of public space to balance the needs of all users.
After the first phase of renovations to Hawthorne Avenue in 2015, the city hired Welch Comer Engineers to help them with phase two of the redesign and reconstruction, this time between Walnut Street and Crestview Drive.
The project provided for the narrowing of the roadway, eliminating on-street parking, then reconfiguring the extra space for a shared-use pathway and a wider sidewalk separated from the street by a “hardscaped” buffer. The buffer was made primarily of colored and scored concrete punctuated with drought-resistant trees that would require little to no irrigation or maintenance.
This phase of the Hawthorne Avenue reconstruction faced challenging road profile grades of up to 13 percent, meaning driveways frequently didn’t match up with the road, a situation that would make travel by the disabled difficult to impossible. Also, the ground beneath the city is mostly clay and silt, which is not ideal for building heavily traveled roads.
Welch Comer worked with a geotechnical firm to design a cement-treated base to strengthen, or “bridge,” the weak material. Once the subgrade elevations were established, specific quantities of cement and water were mixed with the clay/silt soils to create a 10-inch layer of rigid foundation material over which sealing, leveling and asphalt were applied.
This construction innovation was even used under the pedestrian ramps to prevent seasonal differential frost heaving between the road and the ramps.
The ever-present groundwater obstacle was another challenge in this project. Groundwater was so prominent that it was actually seen flowing into open trenches. Waterline and storm sewer construction required excavating deep into saturated clay soils and flowing water. Any saturated material removed from these utility trenches was replaced with existing base rock and ballast material that was reclaimed from the existing road section.
According to Eric Durpos, municipal services administrator for Colville, “Welch Comer’s skill in helping the city prioritize, develop a vision, and construct community-inspired projects are some of the reasons our collaboration has resulted in successful projects like Hawthorne Avenue, Walnut to Crestview.”