A New Angeles Crest Highway Bridge -- Rivers, Rocks and Debris Can Now Run Under It
Due to the nature of the terrain at the construction site, including a 75 percent mountain slope, a bridge was designed that would allow rain, snow run-off, and normal erosive debris to slide under the roadway, avoiding future erosion.
by Marlene Martinez, Caltrans District 7, Public Affairs
The re-opening of this scenic portion of Angeles Crest Highway, State Route 2, has been eagerly awaited by vacationers, sightseers, hikers, skiers, locals and emergency service providers. Earlier this year, District 7 awarded a contract for repair and construction that began in June.
A severe 2005 winter storm resulted in 17 extensive damage sites along a 10-mile section preventing re-opening of the of Angeles Crest Highway, a mountainous road that provides a direct route from Los Angeles County to Wrightwood, a small resort community. Repairs to these 17 sites were completed summer 2008 through funding by the Federal Highway Administration, Emergency Relief Program.
A set-back caused by a March 2006 storm compounded the difficult effort to complete repairs in this area. The storm caused a washout of a road section and its supporting fill slope in a remote area near the Los Angeles County and San Bernardino County lines.
Current construction activities, transporting materials, supplies and specialized heavy equipment have required additional time and care.
Caesar Resler, Caltrans Resident Engineer responsible for this project, points out that this construction project is complicated by the mountainous terrain and remoteness of the site, which is only accessible over a narrow, winding road.
Angeles Crest Highway is a 66-mile two-lane segment of State Route 2, between Foothill Boulevard, in La Canada Flintridge in Los Angeles County, and State Route 138 in San Bernardino County. The highway was originally intended as a fire access road when construction began in 1929. With the advent of World War II, construction stopped in 1941, and resumed in 1946. The highway opened in 1956. Most of the route is a scenic mountain highway through Angeles National Forest, federally protected land with little residential or commercial development. The road summits at a 7,903 foot altitude, making it one of the highest roadways in Southern California.
Due to the nature of the terrain at the construction site, including a 75 percent mountain slope, a bridge was designed that would allow rain, spring snow run-off, and normal erosive debris to slide under the roadway, avoiding future erosion.
Caltrans maintenance crews regularly remove rockslide debris from Angeles Crest Highway during spring, summer and fall months. In winter, the highway is routinely closed late in the year due to rain and snowstorms and resulting road wear and tear.
Caltrans determined that a concrete bridge, as compared to a metal structure, would minimize maintenance requirements, be more economical to construct and could more quickly be constructed. The final design is a simple span bridge whose only roadbed support is an abutment at either end.
Construction has been completed on two supporting abutments; each with four supporting piles, made of concrete and rebar. The abutments extend down 45 feet from the road into solid bedrock and painted with a protective epoxy coating, according to Andrew Ponzi, Caltrans Senior Structural Engineer on the project.
Girders to support the roadbed were formed of high strength concrete (9,000 PSI) with air entrainment, intentional creation of tiny air bubbles in concrete, that allows expansion without cracking. The weight and length of the girders spanning the abutments had to be adapted to Angeles Crest Highway weight restrictions and to the curving road.
Eighteen pre-cast concrete girders were delivered to the staging site then spliced, or assembled, into six larger girders by passing high strength cable though ducts in each girder, and stressing, or pulling, the cable. Each finished girder is eight feet tall, 208 feet in length, and weighs approximately 340,000 pounds.
The girders were transported nearly one mile using a specialized heavy transport system that can be adapted to transport up to1.5 million pounds. The system provides 51,000 pounds of counter weight and consists of a prime mover truck and two separate six-axle goldenhoffers, or dollies, which move in any direction and utilize self-leveling devices. Each girder can be safely transported over the curving road and maintained level over the 5 percent upgrade.
At the bridge construction site each girder is lifted and fitted into the two supporting abutments. Perhaps this month, weather permitting, the last of the six girders will be installed, then, construction of the roadbed and safety barrier will follow. Finally, the mountain will be graded to allow erosion debris to slide under the bridge.
Caltrans anticipates completion of the bridge by this winter, weather permitting, however, Angeles Crest Highway is scheduled to re-open summer of 2009. At that time, this portion of the Angeles Crest Highway will be returned to the eagerly awaiting vacationers, sightseers, hikers, skiers, and local residents to enjoy once again.