Beaverton, Ore.— DBM Contactors Inc. provided a value-engineered design-build solution that saved the Oregon Department of Transportation in excess of $150,000 on its $1.15-million portion of a $34-million highway improvement project. Seattle-based DBM utilized a non-reticulated micropile wall instead of traditional drilled shafts for the 617-lineal-foot retaining wall on U.S. 26, Cornell Road in Beaverton.

The permanent earth retention wall was directly adjacent to the westbound lanes on a busy four-lane highway. Lane closures were not permitted during the project requiring DBM and the general contractor, Mowat Construction Co., to provide traffic maintenance facilities in order to utilize the existing shoulder for construction staging. Despite winter weather conditions and heavy traffic the job was completed on schedule.

DBM crews drilled 23 micropiles at approximately 2 feet to 4 feet on center. The micropiles consisted of roughly 7.5-inch-diameter steel casing with a 1.75-inch central reinforcing steel bar, and extended to 30 feet deep. Ninety-eight permanent tieback anchors were installed at a steeply inclined angle from horizontal in order to remain within the existing right-of-way. The anchors and micropiles were tied together with a reinforced concrete grade beam to complete the retaining wall structure.