Public Works Infrastructure

Dumas Road improvement project

Location: Mill Creek
Owner/developer: City of Mill Creek
Project team: Marshbank Construction, general contractor; Mowat Construction, concrete contractor; KPG, architect; CivilTech, structural engineer; Rinker Materials Northwest, ready-mix supplier

Dumas Road, between state Routes 527 and 96 in Mill Creek, consisted of two narrow lanes with a winding alignment, no shoulders and trees close to the travel lanes. To correct the unsafe condition, the road was widened and precast barrier walls and cast-in-place retaining walls were built.

One of the goals of the project was to protect the natural environment of the corridor by preserving as many trees as possible while conforming to the city’s vision of a national park look.

The project included major earthwork, with excavations to 25 feet. The project’s two largest retaining wall sections were 950 feet long and up to 18 feet tall. The retaining wall was cast in place and covered with formliner texture on the back. Stone facing was installed on the front side and the entire length of each column on the back. A continuous custom-designed railing was installed on top of the wall.

The 3-foot-tall barrier wall provides separation between motorists and multipurpose trail users. It also was clad in stone facing.

The project included installation of underground precast detention and water quality vaults, along with about 4,000 square yards of 4-inch-thick concrete sidewalks.