PacWave South is the nation’s first grid-connected, pre-permitted wave energy test facility under development by Oregon State University and the U.S. Dept. of Energy. The $12-million PacWave South Underground Construction project will feature four subsea power cables for transmission of up to 5 MW of electric power from each of the test berths to the Utility Connection and Monitoring Facility (UCMF). Scope included installation of four one-mile-long,10-in.-dia offshore conduits located up to 120 ft below the seafloor. Placing these conduits required horizontal directional drilling (HDD) trenchless methods from Driftwood Beach State Recreation Site to the offshore exit on the seafloor. Next, crews built a large five-chamber concrete vault structure spanning 10 ft by 14 ft by 73 ft beneath the Driftwood parking lot to accommodate the splice and transition from offshore to onshore cables. Finally, the team built an approximately 0.5-mile-long intersect HDD bore from Driftwood to the UCMF that included a bundle of five HDPE conduits, crossing under sensitive coastal wetlands and Highway 101.

Photo by Dan Hellin

Design and construction took into account the Oregon coast’s harsh offshore environment, which includes significant corrosion potential and challenging environmental conditions. Strategies included a specialized epoxy coating, an active cathodic protection system, special joint construction, a wax joint sealant, desiccant drying and pressurized nitrogen packing of the conduits. A specialized “bullnose” on the offshore end of the conduits sealed them from seawater and sand intrusion.

Photo by Dan Hellin

To work around conflicting surf zones and sensitive wetlands, the team used geologic assessments and geophysical profiles coupled with select geotechnical borings outside of sensitive areas to better understand the geologic formations and their potential to interfere with the HDD.

Photo by Dan Hellin

To avoid using an offshore construction barge, the team pushed a high-strength steel conduit into the HDD borehole from land at Driftwood, using specialized conduit joints and end cap to keep the inside of the conduit dry and pressurized, but still allowing for future removal to install the cables. Crews installed 4.5 miles of HDD in 6 months, achieving an on-time and within budget completion in May 2022.