The I-5 Corridor in northern San Diego County is a busy area with overlapping transportation modes designed to benefit travelers, consumers and residents.
SANDAG (San Diego Association of Governments), working with Caltrans, is seeking to enhance convenience and efficiency in the area by rebuilding a 308-ft. bridge over Batiquitos Lagoon. The bridge will be double-tracked as part of the 0.6-mi. expansion enabling both passengers and freight to travel quicker and more efficiently than the aging single-track bridge currently in place.
The contractors on the $166 million project are Flatiron, Skanska and Stacy and Witbeck.
Stephen Fordham, senior engineer, is supervising the project for SANDAG.
"The old bridge was built in the 1940s and consists of 22 spans each 14-feet apart supported by timber piers constructed of wooden piles," he said. "The piles, similar to a wooden telephone pole, support the existing rail bridge over the lagoon. "As a single-track bridge, trains sometimes have to wait for a train to pass by in the opposite direction before proceeding over the bridge. Now, when the new bridge is built, traffic will be able to move both northbound and southbound simultaneously."
Nearly 400,000 vehicles are shipped into the nearby Port of San Diego.
"When the bridge is finished, it will assist with reducing the creation of greenhouse gases," Fordham said. "Shipping the cars by freight is more cost-effective than by truck. The new double track, which will support more reliable service and could also draw more commuters to travel by rail rather than by car, potentially providing more environmental savings."
Temporary Trestle Constructed
The SANDAG team built a temporary work trestle across the lagoon to support the cranes and heavy equipment, which is a vital part in the construction of the new bridge. This temporary work trestle also allows train traffic to continue across the current bridge without interruption to train operations while the adjacent new bridge is constructed.
The new bridge will be 336 ft. in length and will be supported by five sets of six cast-in-steel-shell piles (CISS) and two new bridge abutments totaling six spans. Each span consists of four precast concrete girders 56 ft. in length.
The construction team used pile-driving rigs to drive the CISS piles into the lagoon bottom to support the bridge. Each of the 42 CISS piles is constructed of 1-in. thick rolled steel and is formed into 3-ft. diameter tubes. The piles were driven approximately 120-130 ft. into the lagoon bottom to support the new bridge.
The upper portion of each pile will hold epoxy-coated rebar and will be filled with concrete, followed by a concrete pier cap and the precast concrete girders. A total of 24 girders were placed, each 56 ft. in length 7 ft. in width and 4 ft. in depth. Once the bridge is in place, it will be covered with decking and railroad ballast rock; then, the railroad ties and rails will be set in place.
The project is under the permit guidance of both the United States and California departments of Fish and Wildlife. The lagoon is home to two productive least tern nesting sites, and SANDAG, in following the permit guidance, scheduled the construction activities to account for this annual breeding season by significantly limiting construction activities between April and September each year.
More importantly, the project is rehabilitating one of the two least tern nesting sites that was eroded by wave and tidal activity.
Refreshing Beaches
SANDAG also will be placing approximately 50,000 cu. yds. of large boulders around the two bridge abutments to protect the bridge from constant wave and tidal action. A portion of the existing rock slope protection used on the existing bridge will be reused for the new bridge.
In addition, with the placement of the new rock slope protection, some sand excavated from the lagoon will be used for beach sand replenishment.
The new bridge and related work at Batiquitos Lagoon will require some 365,000 lbs. of steel, 2,000 cu. yds. of concrete, 50,000 cu. yds. of rock and 50,000 cu. yds. of soil excavation.
Although Fordham described the construction equipment needs as "standard," it still means assembling an impressive array of iron, including long-reach excavators, off-highway dump trucks, vibratory hammers and cranes.
This project is part of the North Coast Corridor (NCC) program and represents an investment of more than $6 billion in the San Diego economy over the next few decades, including more than $250 million to preserve and enhance coastal habitats and access.
Key partners in the program include the North County Transit District (NCTD), the city of Encinitas, the city of Carlsbad, Caltrans, the California Department of Fish & Wildlife, California State Parks and the California Coastal Commission.
Not only will the bridge project be a boon to commerce, but it also will protect an important environmental area. The Batiquitos Lagoon is a vital nesting area for the California Least Tern. Although the 561-acre lagoon is off limits for boats and the public, it is sure to be embraced by outdoor enthusiasts who will appreciate its existence as a game sanctuary and bird estuary.
The project is funded by TransNet and Solutions for Congested Corridors Program grants from the California Transportation Commission. Work is about one-third complete for the new bridge.
SANDAG officials estimate that the bridge will be finished by 2028.
Fordham sees the Batiquitos Lagoon double-track project as an important link with other jobs in the Southern California transportation system.
"This project, together with the San Elijo Lagoon Bridge and Pedestrian project, is all part of the North Coast Corridor Program, which will improve highway, rail, and bike travel in the San Diego region along the coastal Interstate 5 corridor," he said. "The work will improve commuter rail transportation options and should further encourage ridership on Amtrak and COASTER trains." CEG
