Photo: Brightline
The less disruption construction projects cause to surrounding areas, the more smoothly they tend to go. This can be accomplished in a number of ways, from timing deliveries or haul to never coincide with rush hour traffic, to reducing a project’s footprint outside of the immediate construction site. Minimizing disruption becomes a bigger challenge, however, when construction is being done underground, particularly underneath a roadway, which can cause traffic issues for months, or longer, as the roads must be shut down.
An innovative tunneling method known as box-jacking has been gathering steam, enabling crews to construct an underground tunnel much quicker than when using typical underpass construction. A major train tunnel project going on right now in central Florida just outside of Orlando International Airport is expected to take only two weeks, whereas the same project could take up to a year with traditional methods.
What is Box-Jacking?
Although it’s a relative newcomer to U.S. construction projects, box-jacking has actually been around since the 1960s. The method involves precast concrete boxes, which are either made on-site or prefabricated and transported to the jobsite. The boxes are positioned where they will be installed and slowly pushed into place by high-powered hydraulic jacks. At the same time, excavation equipment is used from within the box to remove the soil in its path. To help it slide into place, each box section is lubricated on the outside. In essence, the method forces the concrete box through the dirt, rather than requiring extensive excavation and demolition.
The box-jacking method has been used worldwide to great success when installing storm drains, pedestrian paths, crossings for wildlife, and roadways. Brightline Trains is leading the project outside Orlando in collaboration with Granite Construction, making it one of the first U.S. companies to apply the method. The finished project will connect Miami to Orlando via high-speed rail.
“This box-jacking method began as an idea that Granite Construction brought to Brightline as a way to use construction technology to build two underpasses along the busy corridor between Orlando and Cocoa that would minimize the impact to traffic,” said Michael Cegelis, Executive Vice President, Rail Infrastructure, Brightline. “We are constantly working with our contractors to implement the most innovative and advanced approach to construction, and Granite responded with this innovative technology that is proven in Europe but not widely utilized in the U.S. It will reduce the period of traffic detour from many months to weeks.”
Why is Box-Jacking Preferred to Standard Methods?
Box-jacking uses a trenchless method. This means no pre-dug trenches at either the surface or street level. It is, therefore, minimally invasive to the ground or roadway above where the concrete boxes are being installed, allowing such projects to be finished without causing a major disruption to traffic patterns or surrounding buildings.
Box-jacking is slow going, but it’s considerably less invasive than traditional Tunneling methods using explosive demolition or road closures.
Make no mistake: These boxes we’re talking about are enormous. For Brightline Trains’ Orlando project, each box weighs over 3,000 tons and is more than 30 feet tall. Forty workers doing 12-hour rotating shifts around the clock will be advancing around 3 feet per hour.
In traditional tunnel digging, huge volumes of displaced soil and other debris must be continually carted away from the jobsite. The trucks required for the task contribute to traffic snarls, pollution, and other disruptions at the surface, even though the work is being done underground.
Over the years, building crews have successfully completed some incredible underground construction projects to facilitate transportation, many of them true marvels of engineering and design. Tunneling has traditionally been time-consuming, dangerous work, so the introduction of the box-jacking method to construction projects in the U.S. will likely be a welcome addition, for the workers underground as well as the drivers and pedestrians above.
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