Pipe jacking underneath railroad tracks was used on a short but challenging project in the City of Coralville, Iowa, in order to extend a pedestrian bike trail last winter.
The City of Coralville is a suburb of Iowa City, with a population of approximately 18,200. The City is also home to many pockets of student housing for the University of Iowa and the bike trails are a popular attraction for this group. Currently Coralville has more than 20 miles of recreational trails and overwide sidewalks that connect through the community and as Coralville grows, city leaders have identified approximately 40 additional miles of trail that could be a part of future development, the City of Coralville’s Web site said.
The Clear Creek Trail is a connection from the Clear Creek Bridge on Highway 6, running south to the Mormon Handcart Park parking lot, according to the Web site. The connection under Highway 6 from north to south at the Clear Creek Bridge by McGurk Meyers was completed in fall 2007, along with a boardwalk south of the Iowa Interstate Railroad tracks going to University student housing and over to the Mormon Handcart Park.
A tunnel was needed to allow pedestrian bike traffic to continue on to the boardwalk, which was in a protected wetland area. The 88-ft tunnel was to be constructed under railroad tracks. Though the tunnel itself wasn’t great in length, it presented the contractor, Iowa Trenchless, with several challenges from the amount of cover it had to work with, the weather to the wetlands, where the tunneling machine would punch out into.
The project was bid through the Iowa Department of Transportation. Metro Pavers was the general contractor. VJ Engineering was the project’s design engineering firm, deciding on the use of pipe jacking as the installation method.
“[Given the jobsite conditions,] pipe jacking was the only way this job could have been done,” said Jason Clark, president of Iowa Trenchless, Panora, Iowa.
The concrete tunnel was to have a 12-ft outside diameter, with a 10-ft inside diameter. The pipe was supplied by Cretex Concrete Products. Iowa Trenchless used an Akkerman 1200 Excavator Shield to construct the tunnel and an Akkerman 5000 Pipe Jacking Unit to jack the pipe into place.
The project site was located adjacent to the Iowa River and the tunnel would be constructed parallel to it. Work space was tight and Iowa Trenchless needed special permission from Peterson’s Iron & Metal (a scrap yard) to construct its 35-ft by 15-ft bore pit. In order to do so, the piles of scrap had to be moved. But before Iowa Trenchless could construct the pit, a high-pressure gas line buried underneath the river and project site had to be located.
“That high-pressure gas line was actually directly beneath our bore pit. So our first challenge was to locate that. It was put in a long time ago and we had a heck of time finding it,” Clark said. “Afterward, we had to drive metal sheeting into the pit to try to keep the ground from moving underneath the tracks and maintain the integrity of the railroad bed.”
“We had maybe 5 ft of clearance under the tracks to work with and that’s not much. There was potential of losing the railroad tracks, as there was little cover and the ground was loose,” Clark said, noting that consultation with Iowa Interstate Railroad was needed during the pre-planning phase. “
The Akkerman 1200 Excavator Shield was launched on a Thursday and moving 20 ft or so a day, the machine punched out on that Sunday. The Akkerman 5000 Pipe Jacking Unit followed behind, jacking the concrete pipe and pushing the tunneling machine through to the other side.
Because of the wetlands area on the punch out side of the tunnel, Iowa Trenchless had to find a way to keep the area undisturbed. Clark rented a 500-ton crane from Dawes Cranes Co. in order to pick up the tunneling machine from the exit side and swing it back over the tracks, setting it down on the scrap yard side of the tunnel. It was due to the wetlands that the boardwalk area was built.
“Getting the TBM out of the wetlands area was difficult. It was quite a ways to swing a tunneling machine like that, about 120 ft over the tracks, but that’s what we did,” Clark said.
While the pipe jacking aspect was routine, the weather conditions the crew worked in were adverse. The project was handled in December 2008, with temperatures dipping below zero at times during construction. Wind chills reached -20 F and there was some snow.
“The day we lifted the TBM with the crane was the nicest day we had on the job. It was really cold. The crew did a great job of working in these weather conditions,” Clark said. “Many companies may have shut down with it being that cold but we just kept going.”
Clark said everyone was pleased with the outcome of the job. “The job went very well and [the city] was pretty happy with what we did.”
Sharon M. Bueno is managing editor of Trenchless Technology.