Building Sorrento to Miramar
Flatiron, as managing partner of a joint venture, was responsible for the $24.7 million bid-build contract on the first phase of the Sorrento to Miramar Double Track project that comprised of 1.5 miles of new track, including crossovers and turnouts, parallel to the existing line from south of Sorrento Valley Boulevard to east of Interstate 805. The project was the first of two construction phases that helps speed passenger and freight rail services by straightening the slowest, steepest, and highest curve territories of any segment on the Los Angeles-San Diego-San Luis Obispo (LOSSAN) rail corridor. This stretch of single track between Sorrento Valley and Miramar Road caused a significant bottleneck to rail traffic. Due to the sharp curves and steep grade, train speed was restricted to 25 miles per hour. The project improved schedule reliability by increasing train speeds and allowing passenger and freight trains traveling in opposite directions to pass each other.
Flatiron demolished and replaced a 1940s era wooden trestle with a new 140-foot long double track bridge. This steel bridge was built on cast-in-place abutments and founded on driven steel pipe. To straighten the curvature of the current track alignment, crews constructed ten retaining walls—five different types due to varying geologic conditions—and embankments. This required working closely with SANDAG and their designer to construct the walls and new embankments while maintaining existing rail traffic and minimizing encroachment on neighboring properties. Special track work and signaling was also installed along the route.
140-foot long double-track steel bridge
1.5 miles of new track, crossovers, and turnouts
Work adjacent to and within active railroad corridor
Straighten curvature of current track alignment
Ten retaining walls of five different types
Saving both time and money, Flatiron proposed using innovative permanent soldier pile tieback walls on a portion of the project to SANDAG as a value engineering alternative to conventional reinforced concrete walls. This alternative wall design consisted of drilled-in soldier piles with temporary treated timber lagging between, and a permanent rock sculpted shotcrete architectural facing. Lateral support of the wall was provided by permanent tiebacks at taller wall heights.
Crews faced challenges working adjacent to and within the active railroad corridor. More than 50 trains a day operate on the Sorrento Valley segment of the LOSSAN corridor and pass through the construction site. Crews scheduled work around the train schedule for increased efficiency. The team also put special safety procedures in place to protect workers and the public.
The project also included environmental considerations. The new double-track bridge crosses over Carmel Creek, home to an endangered species of shrimp. Crews conducted environmental compliance monitoring and a project biologist monitored construction over the creek. In addition, one end of the project was adjacent to an ancient Native American village. Paleontological and archeological monitoring was conducted, and nearby excavation was screened for artifacts.