Innovative Construction Helps Caltrans Replace Pfeiffer Canyon Bridge in Record Time
With the October opening of the new Pfeiffer Canyon Bridge on State Route 1, and the restoration of a vital link between Big Sur and the communities beyond it, Caltrans (California Department of Transportation) has completed a massive undertaking, using innovative methods, in a remarkably short time frame.
The new $24 million single-span steel bridge replaces a 49-year-old concrete bridge which was demolished in March. It had been damaged in one of many landslides caused by severe winter weather in the region. The opening of the new bridge brings an additional 35 miles of access along Route 1, and has reconnected the southern section of Big Sur - which has been effectively isolated since the landslides - with the rest of the community. Because of one of the other landslide-affected areas, to travel south along the complete Big Sur route will require taking the Nacimiento-Fergusson Road detour until late in 2018.
The old bridge was closed to pedestrian and vehicular traffic February 15, 2017, after heavy rains caused a landslide under the structure, damaging one of its main support columns. The new, single-span, composite welded steel girder structure was built without the columns that made the previous configuration vulnerable to landslides. Golden State Bridge, Inc. of Benicia, California, served as the primary contractor on the bridge replacement project.
A man walking underneath the bridge in February first noticed the base of one of the pillars was moving, and cracks had appeared in the cement at the top of the pillar; he alerted State Park rangers, and Caltrans closed the bridge shortly thereafter. The bridge, which was built in 1968, was demolished over the span of a week beginning in early March.
Cooperation and Coordination Helped Accelerate Emergency Project
While the bridge itself and the construction method employed are certainly impressive, perhaps most impressive is the speed with which the entire project was designed and built, and the high level of coordination and cooperation between various agencies which made the swift completion feasible. As Caltrans' David Silberberger, who served as the Project Manager, points out, "This would normally have been something like an 8-year process - if all the normal environmental, design, ROW, and construction processes had been required. But we completed the construction in seven months.
"This bridge was recognized as an Accelerated Bridge Construction project. Since this was designated as an emergency contract, we were able to use unique solutions with the approval of the Federal Highway Administration, and could select a contractor without going through the standard bid process, which itself would have taken a long period of time. We had worked with Golden State Bridge before on several major Highway 1 projects, so we were able to work seamlessly with them, basically as a team, right from the beginning."
Silberberger held his first formal Caltrans internal meeting only 17 days after the damage was discovered. Simultaneously, local public officials, politicians and Caltrans management established a "unified command". This group scheduled regular weekly meetings, as did Silberberger's own project team. "We developed an incredible momentum, with a congressman and state legislators, among others, following the progress," he comments. "Everyone on the Caltrans project team recognized that this was a true emergency, and had their game face on. They came ready to rock and roll."
Caltrans Bridge Construction Engineer Neil Weller adds, "Caltrans is a big organization. It was great to see how the various functional units worked so well together, and showed what can be done when so much is on the line. And due to the location, there were multiple agencies involved. To get all the permits required would itself usually take several years."
Multiple Landslides Virtually Isolated Big Sur Region
Big Sur is situated on a rugged stretch of California's central coast between Carmel and San Simeon. Bordered to the east by the Santa Lucia Mountains and the west by the Pacific Ocean, it's traversed by the narrow, two-lane SR-1, which is known for its winding turns, seaside cliffs and coastline views.
The slide at Pfeiffer Canyon was one of three large landslides that impacted SR-1 in Monterey County due to record rainfall this past winter. Paul's Slide, located 24 miles south of Pfeiffer Canyon, remains active with public access provided by a temporary traffic signal. Closer to the San Luis Obispo/Monterey County line is the Mud Creek slide, which totaled over 5 million cubic yards of material.
"Highway 1 is a global destination," Silberberger comments. "The Big Sur drive has been called one of the top five coastal drives on the planet. It's spectacular to drive, but very hard to maintain.
"A large business community has built up around it, and it spreads out beyond the coast itself. And then there are all the local residents who live along the route and travel and commute. After the bridge failure, they were all cut off, isolated in what was essentially an island, and could not get daily necessities. The only alternative route to most of this area was a steep, narrow country road.
"When the bridge first started to fail, we initially wondered if it could be saved. But it quickly became apparent that the continuing slide would take out the support column."
Weller relates that once it was determined that the bridge was traversable, with restrictions, a schedule was established whereby one vehicle at a time could cross the bridge on two occasions only before fully closing to both vehicular and pedestrian traffic. The highway was closed 17 miles to the south, making the Big Sur area landlocked; the bridge opening was necessary to evacuate locals and visitors south of the bridge.
"˜Launching' Construction Method New to California
Caltrans immediately began careful consideration of the available options for replacing the bridge quickly. "We usually build concrete bridges, but steel lent itself to this need," Silberberger comments. "And we did not want to use columns again."
Weller adds, "The slope was unstable, and we did not know when it would stabilize. The column had been displaced by the slide. We decided quickly that the best thing to do was to span the canyon, to go over the problem."
Within three weeks of the closing of the old bridge, a preliminary design was ready, according to Silberberger. Getting girder fabrication underway quickly was a critical factor in accelerated completion of the bridge, and the preliminary design allowed the Caltrans team to initiate a nationwide search for the specified Grade 50 steel and begin shipments of it to the fabrication plant before the design was even completed.
The signature feature of the new structure - 15 steel girders, weighing 62 tons each, which span the rugged, deep canyon - were fabricated at the XKT Engineering Plant in the nearby city of Vallejo, then painted by R&B Protective Coatings in the city of Linden. They were delivered to the north side of Pfeiffer Canyon in groups of three and assembled using splice plates and approximately 15,000 bolts to connect them all together.
The structure's design includes no support columns, eliminating structural vulnerability from future slide activity. The new bridge, with 12-foot lanes and 6-foot outside shoulders, has a 315-foot-long span, about 100 feet above the canyon floor.
Once the girders were in position, they were slowly moved across the canyon utilizing a technique called "launching". Contractor Golden State Bridge suggested this innovative process, utilized for the first time on a state highway system project in California, to Caltrans.
To facilitate the launching process piles were installed in the bottom of the canyon, followed by a slab to support a temporary tower. This heavy-duty tower was used to support the weight of the bridge as it was pulled out across the canyon.
The assembled girders were then pulled across the canyon simultaneously with the use of high strength steel strands and hydraulic pistons. As each piston cycled, the assembly was pulled in 12- to 18- inch increments. After each pull, measurements were taken to check for deflection and alignment, ensuring the process was proceeding correctly. This process was repeated again and again, and it took four days to pull the full 315 feet and reach the south abutment. Once across, the girders were 15 to 17 feet above the roadway surface and needed to be raised to remove the temporary support tower, then lowered down onto their supports at the abutments.
After the girders crossed the expanse and the supporting rollers and guides were removed, more conventional methods of construction were completed so that the road could be opened to the public. Rebar was installed, the bridge deck was completed, and the final roadway surface applied and striped.
Final work will continue for several weeks, perhaps until late January 2018, but Pfeiffer Canyon Bridge is already providing access to both residents and travelers. There may be some weekday work which will require a lane closure consisting of one-way reversing traffic control, but no full closures are expected.
Highway 1 remains closed from south of Gorda to north of Salmon Creek, due to the massive landslide at Mud Creek, which occurred in May. A realignment project has begun at that location with completion of a new roadway expected by late 2018.