Alameda Corridor-East Construction Authority
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Civil Engineering magazine/American Society of Civil Engineers
By Catherine A. Cardno, Ph.D.
September 4th, 2012

Railroad Trench to Ease Traffic, Prevent Collisions

A 1.4 mi long stretch of Union Pacific railroad track in San Gabriel, California, will be moved into an open trench 65 ft wide and 30 ft deep in an effort to eliminate grade crossings and improve safety and sight lines. Bridges will carry vehicular traffic over the trench. © Alameda Corridor-East Construction Authority

A new railroad trench is being built in California as part of the Alameda Corridor-East project to prevent crossing collisions and ease congestion.

September 4, 2012?Work will soon begin on moving a 1.4 mi long stretch of Union Pacific railroad track in San Gabriel, California, to a position 30 ft below the surface. The 65 ft wide open railroad trench will extend through the city, decreasing traffic delays and congestion and eliminating the potential for crossing collisions while avoiding any untoward effects on the historic San Gabriel mission (formally, Mission San Gabriel Arcángel). The plan is part of a larger, 2.2 mi long grade separation project that includes four new street bridges spanning the trench that will carry a total of nearly 90,000 vehicles a day.

A concrete floor slab at the bottom of the trench will be wide enough to hold two sets of main line track as well as a service road, according to Phillip Balmeo, P.E., LEED AP, the senior project manager for the Alameda Corridor-East Construction Authority.

?The use of struts across the top to brace the walls was not permitted by Union Pacific Railroad,? Balmeo wrote in response to written questions submitted by Civil Engineering online. ?Instead, the walls will be secured with lengthy tiebacks extending into the soil on the exterior of the trench walls.? Cast-in-drilled-hole piles will be used with the tiebacks to create the walls of the trench, which will rise at 90-degree angles to the concrete floor.

Top-down construction is being used for the project. Once the piles and tiebacks are installed for the wall system, precast-concrete beams with cast-in-place concrete decks will be placed for the decks of the four bridges that will carry traffic across the trench, Balmeo explained. Excavation of the trench will then be completed, the walls will be finished, and the bottom slab will be placed.

The rail line?s proximity to the San Gabriel mission (formally, Mission San Gabriel Arcángel), together with a requirement that views of the structure be preserved, influenced the decision to place the rail line in a trench. © Alameda Corridor-East Construction Authority

The use of an open trench for routing trains through a city is not typical, Balmeo said. However, one of the deciding factors was the ?proximity of the historic San Gabriel mission, which was founded in 1771 and which marks the first non?Native American settlement in the region,? he said. ?The National Historic Preservation Act of 1966 requires that view corridors be maintained for historically significant areas, which precluded the use of an elevated or flyover structure to grade separate the railroad main line [from the] streets.? Lowering or elevating the roadways was also ruled out by a desire to ensure that construction would not adversely affect the mission itself or the city?s Mission District.

The area?s Tongva Indian history and the architectural style of the Mission District will be reflected in project enhancements, according to Balmeo, including short concrete barrier walls at the two crossings located near the mission.

The railroad trench project is expected to create the equivalent of 8,964 full-time jobs and is a necessary portion of the Alameda Corridor-East project, according to Paul Hubler, the director of government and community relations for the Alameda Corridor-East Construction Authority.

?The project will reduce locomotive horn and crossing bell noise, congestion, air pollution estimated at 213 tons/year of air toxins, and greenhouse emissions by 2030,? said Hubler, who also replied to written questions submitted by Civil Engineering online. Emissions will be lowered because the rail trench will eliminate an estimated 1,744 hours of vehicle delays that are currently experienced at the four crossings each day. What is more, placing the rail line below the surface will eliminate the potential for crossing collisions, projected to occur approximately once every four years, and eliminate delays experienced by emergency vehicles.

The San Gabriel trench project is the Alameda Corridor-East Construction Authority?s largest single undertaking, according to a press release issued by the authority. The entire Alameda Corridor-East project encompasses 70 mi of freight rail main lines east of the original 20 mi Alameda Corridor, which was completed in 2002 (see ?The Train Line,? Civil Engineering, September 2002). The aim is to ensure that cargo containers can be safely and quickly moved from the busy cargo container ports in Los Angeles and Long Beach to points eastward by train rather than by truck.

A contract for $172.6 million was awarded to a heavy construction unit of Chicago-based Walsh Construction Company last month, and work on the San Gabriel trench is anticipated to begin this fall and take five years to complete. The overall cost of the San Gabriel trench project is estimated at $498.5 million, according to the project's fact sheet.