Landslide Mitigation Measures Fail To Save Plan To Build Bypass Bridges in Oregon
After millions of dollars in costs and years of delays, the Oregon Dept. of Transportation has labeled as a failure the landslide mitigation on an unfinished four-mile stretch of U.S. 20 between Pioneer Mountain and Eddyville.
In an attempt to bypass a windy 10-mile roadway prone to landslide damage, Yaquina River Constructors—whose parent company is Watsonville, Calif.-based Granite Construction Co.—planned to build a total of 11 bridges for its design-build contract. Seven are now complete. The remaining four bridges were to range from 600 ft to 1,100 ft, with heights between 100 ft and 210 ft.
In 2007, Granite tried to end its contract after finding evidence of ancient landslides (ENR 7/30/07 p. 11). A $61-million agreement settled the dispute and pushed the finish to December 2011 from October 2009. Work resumed in 2009.
The landslide mitigation work added to the contract has failed, however, says ODOT, now in a dispute with Yaquina over responsibility for the costs and delays of the additional engineering and construction. In July 2011, the two parties presented the contract to a dispute review board. The board stated that Yaquina remains responsible for a successful design, but that differing site conditions did exist. Both parties can file a claim.
The project originally was budgeted at $140 million but grew to $217 million in 2008, with $194 million spent without a finished roadway or a workable design. The new coastal alignment slices through forested land, sometimes on 40° slopes in a mountain range drenched with as much as 100 in. of rain annually.
In 2010, lateral loads from adjacent fill and subsurface ground pressure from the landslides caused bents erected for one of the four bridges to shift as much as 2 in.—a scary outcome considering the 75-year expected life span, says Joe Squire, ODOT project manager. Since then, construction has stopped on the bridges. The contractor continues to collect data. Citing "too much force," ODOT announced the failure this fall and sent Yaquina back to the engineering table, says ODOT spokesman Richard Little.
With columns up to 120 ft tall, one inch of movement at a column's bottom can translate to three feet at the top. "We have a very classic bent," Squire says, with drilled shafts supporting columns and bent caps. The 8- to 10-ft-dia, reinforced-concrete shafts are drilled 55 to 95 ft below the original soil surface.
Some 3.1 million cu yd of earth has been moved, with large buttresses and shear keys installed at the slope bottoms in hopes of holding back four slides at the Eddy C, Eddy B, Crystal Creek and Cougar Creek bridge locations. The $7.4-million Eddy C bridge has been compromised by continued landslide activity and its future remains unknown, according to ODOT. The bridge columns for Eddy B were demolished in March 2010, and Yaquina wants to remove an out-of-plumb bent at Cougar Creek. The five sets of columns and two end bents at Crystal Creek appear unmoved, Little says.