When a rockslide slammed 20 yd.3 of cliffside onto the Kamehameha Highway in March 2000, it cut off access to homes, businesses, and tourist destinations on Waimea Bay’s North Shore on the Hawaiian island of Oahu. The state geologist determined the cliff above was unstable, resulting in closure of the highway for an indefinite period. Closing the highway forced 12,000 commuters to circle the island to reach Honolulu and other destinations. As short trips turned into multihour expeditions, tempers flared and business profits began to suffer. A few days after the slide, Governor Ben Cayetano declared a state of emergency, and opening the road became a top priority.
Front view of the wall system
Back view of the wall system
Kamehameha Highway workers lay the geogrid behind the wall panels.
An attractive facing is added to the wall, allowing it to blend in with the environment.Realigning the highway proved to be the quickest and most affordable option. The presence of ancient burial caves in the cliff ruled out cutting back the cliff face. The Hawaii Department of Transportation planned to move the highway’s centerline out 25 ft. away from the cliffside and create 1,400 ft. of new roadway with two 11-ft.-wide lanes and a grassy rock catchment area next to the cliff. A 12-ft. rock protection fence would safeguard vehicles, and the road’s bayside would be retained by 850 lin. ft. of retaining wall. As reported in a Project Profile in the July/August 2000 issue of Erosion Control, an emergency bypass road was constructed along the beach using the Presto Geoweb cellular confinement system; it opened on March 18, 12 days after the initial slide, to handle traffic while the new highway section was completed.On April 10, the state awarded a $7.4 million contract to Goodfellow Brothers Inc., with the project targeted for completion in only 60 days. “It normally takes eight months or more to do this type of job,” says Tom Hoen, Goodfellow Brothers’s chief engineer. “We couldn’t make it if there were any weak links in our team.” The team included Healy-Tibbitts Builders, the installation subcontractor; Earth Tech Corporation, consulting engineers; Rocky Mountain Prestress for precasting and fabrication of the wall panels; and Tensar Earth Technologies, makers of the ARES Full-Height Panel retaining wall system that was to be used on the road’s seaward side. Because the wall was in the tidal zone, using steel strips or grids for reinforcement of the wall was ruled out. Tensar air-expressed nonmetallic reinforcing geogrid to Oahu. Rocky Mountain Prestress was responsible for casting the full-height and base panels for the wall and transporting them to the job site. Each panel included embedded tab connections for full load transfer to the geogrid. “It was our first time using geogrid, but it meshed with our existing knowledge,” points out Mike Caron, project general manager. “That helped us finish production early-even with modifications and adjustments to the panels.”Unexpected outcrops meant that some of the base panels had to be reengineered, a process that usually takes one to two weeks. Tensar engineers worked to turn the requests around in less than a day. Along with rock, the installation contractor had to contend with marshy soil and groundwater. On some projects, such conditions would be a prescription for pumping and construction foundations, but here the lower wall panels were installed directly on the subgrade, even in areas with 2-6 ft. of standing water. This saved time by eliminating not only the pumping but also the need for special environmental permits, according to Earth Tech Senior Project Manager Ardalon Nikou. Because the full-height wall panels averaged 17 ft. tall by 9 ft. wide, the entire retaining wall required only 100 units. With traditional articulated panels, about 700 units would have had to be formed and installed. The larger panels cut installation time by about one-third. Much to the relief of the North Shore, the close cooperation and hard work of the project participants paid off. Just 59 days after work began, the community, state officials, and crews celebrated the completion of the project with a party at nearby Waimea State Park. “It wasn’t a normal job by any stretch,” says Goodfellow’s Hoen. “But with a good team and by working ’round the clock, we made it happen a day early and under budget. Everybody should be proud of the way things turned out.”
