Only the fourth concrete arch bridge to be built in California during the past 50 years, the 627-ft. (191.1 m) long Spanish Creek Bridge is currently under construction in Plumas County.
Featuring a 300-ft. (91.4 m) arch span — one of the largest spans in the state —the $12.7 million Spanish Creek Bridge is the 11,000 job funded by President Obama’s American Recovery and Reinvestment Act of 2009.
“There aren’t that many concrete arch bridges in California, [so] the bridge could be an icon for the area,” said Michael Mayor, public information officer for Caltrans District 2, explaining the open-spandrel, concrete arch bridge design was selected because of its relatively low cost and maintenance.
Located along State Route 70 in Plumas County — a county with roughly 20,000 residents — the new bridge will replace the existing, steel truss Spanish Creek Bridge, which was constructed in 1932 and has exceeded its expected service life.
“The [existing] bridge exhibits signs of significant structural fatigue, does not meet modern seismic standards, does not have standard shoulder width, and cannot accommodate some extra large truckloads,” according to a Caltrans fact sheet.
Being built approximately 40 ft. (12.2 m) west of the existing bridge, the new structure will be capable of supporting up to 15-axle oversized loads and features a 75-year design life.
General contractor C.C. Myers began construction of the new bridge on June 14.
Rising 160 ft. (48.8 m) above Spanish Creek, the bridge will feature solid concrete arches that are roughly 8 sq. ft. (0.7 sq m) each and taper towards the bridge’s peak — giving the structure a slender arch profile, Mayor said.
Micro-piles, rather than standard piles, will be used for the bridge’s foundations — with 6,000 cu. yds. (4,587 cu m) of concrete and 1.3 million pounds of reinforcement used to construct the entire bridge.
Adopted from the states of Wyoming and Alaska, the new bridge will feature a see-thru barrier railing that is ideal for snow removal and modified to be bicycle friendly.
As part of the project, a 60-ft. (18.3 m)-tall retaining wall with a natural rock appearance also will be constructed.
Before actual bridge construction can begin, several construction staging areas —one at each corner of the bridge at highway elevation, and one beneath the bridge at stream elevation — will be built. The main construction staging area utilized by cranes, excavators and concrete trucks will be situated beneath the bridge.
“Given the depth and required span of the highway crossing, construction from the highway elevation only, without a staging area below the bridge, is not an option,” according to a Caltrans project report. “Cranes typically used in bridge construction would not have the reach and lifting capability needed to construct the bridge from above.”
Since Spanish Creek is relatively shallow at the project location, a culvert(s) will be placed in the creek channel for the length of the existing and proposed bridges. Clean cobbles, construction fabric, and a layer of gravel will be placed over the culvert(s) to create a level work pad for the main staging area below the bridge.
The project is expected to be reach completion by late 2012. At that time the existing steel truss bridge will be demolished and the Spanish Creek Campground — which lies beneath the bridge — will be reopened.
The construction cost of this project ($12.7 million) is 36.5 percent lower than Caltrans’ original estimate. The $7.5 million in project savings will be redirected to fund additional highway projects.
A Second Significant Bridge Project
To the Northwest of the Spanish Creek Bridge project — in neighboring Shasta County — the construction of the $125 million Antlers Bridge is currently under way.
Located along a portion of Interstate 5, the five-span concrete bridge will be 1,942 ft. (592 m) long and 104 ft. (31.6 m) wide once completed.
As of July 1, earthwork operations were under way with work continuing on one of the new bridge’s abutments. During the second week of July, Tutor Perini — the project’s general contractor — continued to place steel reinforcement and forms, with the pouring of one abutment scheduled for the week of July 19, according to a Caltrans project update.
The $125 million bridge will replace the existing 1,330-ft. (405.3 m) -long Sacramento River (Antlers) Bridge, which was built in 1941 and spans the Sacramento River arm of Shasta Lake.
In addition to new bridge construction, a 0.4-mi. (0.6 km) long section of highway south of the bridge will be realigned and the existing steel truss bridge will be demolished and removed.
Currently that 0.4-mi. stretch of highway includes a series of curves on a six percent grade, which makes the accident rate on that section significantly higher than the statewide average for similar highway segments.
Preliminary construction for the new Antlers Bridge began in November 2009, with actual construction commencing in January 2010. The new bridge will reach completion sometime in 2014.
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