Founded in 1971 as Lynchburg Baptist College in Lynchburg, Va., Liberty University is a thriving educational institution with more than 100,000 students on campus and online, including 12,000 on campus – a long way from the 154 students in its first year. The university, which was also known as Liberty Baptist College before adopting its current name in 1984, is a fully accredited university offering graduate, undergraduate and online learning in more than 350 study areas. Additionally, the Flames athletic teams compete in the NCAA’s Big South Conference in a variety of men’s and women’s sports.
Liberty University is in the midst of a $500 million, five-year campus renovation and construction program to position it for the future. Included in the ambitious plans are the construction of a new library and academic and residence halls. The goal of the campus improvement project is to accommodate 16,000 residential students by 2020. And, in order to improve traffic flow into and out of campus, Liberty also got into the tunnel construction business. Recently, the university completed the construction of twin 130-ft long jacked box tunnels as a means to improve motor vehicle accessibility.
At first glance 100-plus ft long tunnels don’t appear to be anything extraordinary, however, the Liberty University project is believed to be the first North American use of the jacked box construction method in which the box was actually pulled, rather than pushed, into place. The project was designed by Brierley Associates with tunnel construction by Southland Contracting of Ft. Worth, Texas.
The project involved the installation of twin boxes pulled into place underneath Norfolk Southern railroad lines. Utilizing the reaction wall constructed for the first tunnel, the jack system was reversed to install the second parallel box tunnel. Additional roadway work and follow-on work to remove the reaction wall, construct the roadway and reconfigure existing roads remains with final completion anticipated by mid-year.
Completion of the project will allow for two lanes of traffic in each direction to and from the heart of campus near the intersection of Wards Road and Harvard Street, a busy commercial district that is separated from campus by railroad lines. Currently, traffic must use an at-grade crossing to access campus – a crossing that is subject to frequent interruptions from railroad activities.
Elimination of the at-grade crossing will also improve safety and traffic flow. An additional benefit is that the tunnel leads into a new 1,400-space parking structure being constructed, which will help reduce vehicular traffic on the campus itself.
Constructing tunnels to eliminate the at-grade crossing to improve traffic and safety has been envisioned since 2006. “The university has been planning to do this for a number of years, but it had to coordinate with the railroad and the Virginia Department of Transportation,” said Steve Vinci, Senior Geologist with Brierley Associates. “With this connection, traffic on campus will be greatly improved.”
Jeremiah Jezerski, geotechnical engineer and Brierley Associates’ Project Manager, concurred. “Essentially there were two entrances to campus – the main one is at Richmond Highway; the secondary access was the at-grade crossing that would have you cut through a parking lot of a Sonic restaurant to access,” he said. “Leaving campus, you had to cut through the parking lot of an auto body shop. Additionally, anytime there was train activity, vehicular traffic would be shut down – and this happened multiple times per day.”
As a result, the university decided to fund the tunnel access project. Working in conjunction with railroad planners, a cut-and-cover solution was quickly dismissed as being too disruptive to the railroad. Sequential excavation was also considered, but concerns over potential settlement to the rail lines above led planners to another solution. Using digger shields to construct the tunnels was also looked into, but the diameter required to accommodate two lanes of traffic would have required lowering the tunnel depth and increased costs.
In late 2012, the university hired Brierley Associates to design the tunnel. The solution: a jacked box tunnel underneath the railroad embankment. “This solution alleviated some of the railroad’s concerns, but there was still concern about the entire embankment blowing out during the jacking process,” Jezerski said. “So, by building a reaction wall on the opposite side of the tunnel boxes and pulling into place, we were able to confine the whole embankment during the process and alleviate the concerns the railroad had.”
Brierley Associates finished the design in spring 2013 and the project went to bid and was awarded to Texas-based Southland Contracting for approximately $7 million. Southland has experience in the construction of jacked boxes, but nothing like this project, according to Southland Project Superintendent Clay Griffith. “We have jacked large storm drains and concrete pipe segments,” he said, “but this project is completely different because you are pulling the boxes through the ground. By pulling the boxes you are able to keep the compression on the other side of the wall to prevent pushing the entire hill over.”
Preparation work consisted of clearing the railroad embankment, installation of tendon cable casings through the embankment by horizontal directional drilling (HDD), placement of spiling above the alignment, construction of a reaction wall of the launch side using soldier piles and wood lagging, along with other roadway preparations. Following those activities, the launch pit was excavated to grade, a launch slab was poured and a soil nail wall was constructed on the face of the railroad embankment to support the excavation.
Building the Tunnels
When Southland Contracting arrived on site they got to work building the 4.2 million-lb tunnel boxes, which measured 20-ft high by 32-ft wide by 130-ft long. The boxes were cast in place, first the floor, then the walls and roof. Steel plates were cast into the floor, along with ports for Bentonite slurry, to help reduce friction as the boxes were pulled. Additionally, a cutting shield was cast into the front of the box to help dig into the ground.
Southland used six DSI post-tensioning jacks, with a capacity of 765 tons each, to pull the steel tendons through the casings installed by HDD. Once the boxes were constructed and all other preparations were in place, it took Southland 14 days, working around the clock, to pull the first box into place. Crews used two mini excavators at the face in conjunction with a conveyor belt to remove muck from the tunnel as it was advanced into place. The boxes were pulled to within 30 ft of the face, leaving sufficient soil to develop the passive resistance required to counteract pulling forces.
The first pull was completed before Thanksgiving, but crews had to wait till after the New Year to complete the second installation so as to not potentially interfere with railroad operations during the busy Christmas shipping season. Upon returning on Jan. 6, crews made some adjustments, placing the jacks at the rear of the box to reduce buckling of the HDPE tendon casings, and completed the second installation in just under 84 hours.
“Due to obstructions in the top of the alignment, primarily rock that was used as fill when the railroad was built, the tendon casings weren’t as straight as we would have liked,” Griffith said. “As a result, sometimes the tendon casings would buckle instead of collapsing on themselves. By pulling from the back of the box on the second pull, we didn’t have that issue.”
Southland’s portion of the project has been completed. A follow-on contract will be awarded to remove the retaining wall and finish construction of the roadway. It is expected to be online by mid-year.
According to sources, this is the first use of a jacked box tunnel in the United States in which the boxes were pulled into place. “There have been some uses of this method that we found in Australia and Europe, but this is the first pulled jacking application in the country as far as we know,” said John Marcantoni, Project Manager for Southland.
Also involved in the project were TGS Engineering, Norfolk Southern’s consultant, and Elwyn and Palmer Consulting Engineers, the structural engineering consultant for Brierley Associates.