Box-Jacking Operation Moves Rail Underpass in a Weekend
When the Long Island Rail Road considered its options for moving multiple rail crossings below grade, it was anticipating weeks-long service disruptions. But an innovative method developed by an Italian engineer, never before used in the U.S., allowed it to put each new underpass in place with only a weekend shutdown.
The box-jacking system from Italy-based Petrucco uses hydraulic jacks and spreaders to move a cast-in-place concrete box carrying the entire underpass and rail bridge into place in a matter of hours, with limited disruption to railway traffic.
LIRR is using the Petrucco box-jacking method on six grade-crossing eliminations, installing underpasses to keep car traffic off the tracks. It’s part of the $2.6-billion 3rd Track Program, which will extend service for the busy commuter line. The contractor is 3rd Track Constructors (3TC), a consortium of Dragados USA, John P. Picone, Halmar International and CCA Civil. Stantec is the designer for 3TC.
Union crews did the work, although many had never used the Petrucco system before. The first installation, at Urban Ave. in Westbury, N.Y., was performed July 20. The second installation, on Covert Ave. in New Hyde Park, N.Y., on Aug. 24, went even smoother as crews got accustomed to the method.
"We're ahead of schedule on this one," explained Nick Almeter, area manager with Halmar, as he walked inside the concrete box during the jacking operation. He says 3TC's selection of Petrucco's approach was driven by LIRR's need to minimize service interruptions. "This method will require only one double-track outage, basically taking the railroad out of service from 4am Saturday morning, and returning it to them by 9am Sunday morning," he says.
“It’s almost boring, which in construction doesn’t happen too often,” says Anthony Tufano, executive director of the mainline expansion project for LIRR. “It’s an amazing process. How have we not been doing this in the States for years?”
According to Tufano, it's a huge leap forward from how LIRR traditionally does grade-crossing eliminations. "So [with the Petrucco technology] we profiled our tracks beforehand and we excavate, push this bridge in, put the soil back and build a railroad," he says. "If we had done it with a conventional method, we would have had to build abutments while the tracks were there, taken a lot more outages to put those abutments in place, and we would have had to fly a bridge in or roll a bridge in, like when we do a bridge replacement. But this, it's just ingenious."
For comparison, Tufano says LIRR did a grade-crossing elimination further down the line several years ago that took almost three years to complete. "But Urban Ave. and Covert Ave., we will have cars flowing underneath the railroad in six months."
The Covert Avenue box consists of a 112-ft by 40-ft reinforced concrete slab, with 24-ft side walls and two spans on top bearing rail and a roadway. The 2,000-metric-ton concrete box was cast on site, and then slid 58 ft into its final place. Prep work included excavating the underpass and installing sheet piles to shore up the sides. While Petrucco’s method normally calls for sliding the box underneath existing rails, limited site access meant the rail had to be installed on the top of the box.
Staying on Target, Inch by Inch
The box is pushed off of a concrete launching slab, but that slab does not extend the full distance it will travel. At the Covert Ave. site, the box's final position will be half on the slab and half on soil. At the earlier Urban Ave. site, the box's final position was entirely on natural soil. Properly surveying soil characteristics and planning around the environment is critical to the success of the box-jacking method, according to Diego Rodriguez, project manager for Petrucco USA. "For this kind of job, we are talking about millimeters of accuracy," he says. "We have some really experienced guys who know how [the box-jacking system] behaves in all kinds of soils."
Keeping the box level and on-target is key during the move, so a total station set up at one end monitors prisms mounted to the box. If it begins to drift sideways, the hydraulic jacks are adjusted to steer it back on center. If it drifts up or down, the amount of soil packed under its leading edge is adjusted to get it level again. "Right now, I'm monitoring jacking rates and alignment—the horizontal and vertical alignment of this box," explains Almeter, pointing to a digital level and a set of prisms mounted to the corners of the box. The design allows for plus or minus 3 in. of accuracy for the final positioning.
On the Urban Ave. move, the team got within 0.6 in. of the target position, and finished three hours ahead of schedule. Almeter says they learned a few things from that move that they were applying on the Covert Ave. job. "One of the lessons learned was coming up with a better solution to remove the sheet piles quicker so we can start jacking earlier," he says. This shaved considerable time off of the startup during the rail outage, allowing the box-jacking operation to begin earlier in the day.
At Covert Ave., the box began moving at 8:45 a.m. and was in place by 5:00 p.m. All that remained was to link up tracks on Sunday so commuter trains could run on Monday morning. All of this was finished within the outage window that LIRR had allowed.
While the LIRR 3rd Track is the first usage of Petrucco’s box-jacking method in the U.S., it has been widely used in other parts of the world. According to Petrucco, the company has performed similar box-jackings over 1,500 times, in countries including Spain, Canada and Qatar, since the method was first introduced in 1978. “It is simple work, but it is not easy work,” says Alvise Petrucco, inventor of the technology. “From an [engineering perspective] it is very pure.”
N.Y. State's Embrace of Design-Build a Major Factor
New York state’s recent advocacy for design-build project delivery was a key factor in choosing to go with the Petrucco method, according to Phillip Eng, president of the LIRR. “We have 294 other grade crossings to go, and alternative delivery methods like design-build let us do it this way,” he told ENR while touring the Covert Ave. site on Aug. 24.
"Design-build is one of those things where we allow the private sector innovation to come in with concepts to help us accomplish a tremendous amount of work in a short period of time. We’re running the busiest commuter railroad in North America, and how do you replace the mainline tracks and still provide service? And that’s where the partnership between between our workforce and industry is crucial," says Eng. "I don’t know if you can find another commuter rail road that has this many grade crossings in such a short geographical footprint...I would absolutely recommend [the box-jacking method] to others. If it works for LIRR, it’s going to work for other railroads across America."
Eng says the minimum disruption to the rail schedule and the surrounding area was a key reason they went with the method. “This is transformative for LIRR, and we have Gov. Cuomo’s leadership to thank for letting us pursue alternate delivery methods,” he said.