Pipe ramming contractor HURK Underground Technologies overcomes various obstacles to complete culvert project.
As an underground trenchless technique for installing and replacing culverts, pipe ramming is often the most efficient and economical. At times it may be the only feasible option. Such was the case in a southern Illinois railroad culvert installation in flooded ground conditions.
CN Rail Line contracted HURK Underground Technologies of Grinnell, Iowa, to install two 180-foot-long, 60-inch-diameter culverts using pipe ramming beneath the railway in Cairo, Illinois. The culverts were designed to relieve an existing, partially collapsed, 48-inch steel culvert with reduced capacity.
Work began in November 2013. From the start HURK was faced with daunting obstacles. For one, the job site was in extremely wet ground conditions far from the access road.
“This was the most difficult ram the company has performed,” says Jason Pollock, HURK’s director of ramming operations on the project. The project was difficult because of the size and length of the ram and also from complications from subzero temperatures, inundated ground conditions and unexpected obstacles inside the railway substructure.
EQUIPMENT AND CASING
In addition to a 350-series excavator used to create the working pit, HURK brought to the job site a mini excavator, track loader, horizontal drilling machine with 48-inch-diameter posthole auger, 1,300 cfm air compressor, adjustable pipe stands, and 24-inch pipe ramming hammer from HammerHead and appropriate tooling for 60-inch pipe.
The new casing consisted of 30-foot lengths of 0.875-inch smooth wall steel pipe for new culverts set 2 feet apart from each other at an elevation 40 feet below the rail bed.
Staging the equipment and setting up the access pits was the first problem to overcome. Both sides of the roadbed were wetland areas. Only a mile-long drive across cropland Pollock described as “soupy” could be used to get to the installation site. To get to and from the site, HURK used its tracked equipment to pull the company’s trucks across the field most days.
The surface of the railroad bed was about 40 feet above the culvert insertion point. This job site scenario, known as “high fill” or “deep cut,” is difficult to survey. The spot chosen for the installation allowed HURK to stage its equipment just above water. The soggy ground conditions, however, presented another problem. The HURK crew tried to dig a 60-foot-long, 30-foot-wide working pit to a vertical depth of 10 feet at the toe of the railway berm. With each attempt, the pit’s sides repeatedly collapsed, filling the excavation with mud and frustrating the crew.
Pollock and his crew hit upon the strategy of digging just half of the working pit 3 feet lower than the intended working grade. They immediately filled the excavation with 3-inch rock, setting sump baskets in the backfill. Then they quickly excavated the other half. The trick worked. With diesel-powered pumps in the sump baskets dewatering the first half of the pit, they were able to finish the pit to full size.
Once pumping operations started, all six 190 gph pumps ran continuously for four months through project completion, including weekends and Thanksgiving and Christmas work breaks.
Overcoming these complications at this location had taken the crew a week longer than usual to complete the working pit.
The excavation’s size allowed HURK to install both culverts from a single working pit. Each section of casing required the crew to attach the hammer to it, ram the pipe into the berm at about a 2 percent grade, detach the hammer, weld on the next section of pipe, reattach the hammer and continue ramming.
Two welders could complete the root weld and fill passes on the large-diameter pipe to industry specification usually in less than five hours.
Ramming progressed at about 6 inches per minute while the hammer was operating.
MORE OBSTACLES: TREE STUMP AND PIERS
Pollock says that whenever pipe ramming progress drops to less than 1 inch per minute, he believes the pipe is cutting through tree roots or rock, or is pushing an obstacle out of the way.
“So when the progress stopped at the 90-foot mark ramming the fourth length of pipe and would budge no further, even after 30 minutes of hammering, we suspected the pipe had met an immovable obstacle,” Pollock says. “Continued ramming could have damaged the pipe or hammer.”
The crew stopped pipe ramming operations to detach the hammer and auger out the spoils in the pipe.
The pipe diameter permitted the crew to physically enter it to inspect the obstacle, and they discovered a 5-foot-wide tree stump perfectly aligned to block their 5-foot-wide pipe.
“You couldn’t have hit that tree that precisely if you had been trying to,” Pollock says.
Pollock figured the tree must have been felled to make way for the original berm construction, but rather than removing it, it must have been simply covered over. Burial in the wet conditions had preserved the wood remarkably well. The crew cleared the stump away from the pipe path piece by piece using small, electric chain saws. Pipe ramming then continued.
Shortly after they had resumed pipe ramming operations, progress was once again halted. The hammer was removed, the pipe was augered out and the crew crawled inside to see what the new obstacle might be.
“This time it was a wooden pier, the first of many we discovered every 10 to 20 feet from that point on,” Pollock says. “The piers were remnants of a bridge or train trestle that predated the berm. Piers were encountered on both of the pipe runs.”
Except for these two obstacles and the harsh working conditions, there were no other complications. Undaunted, HURK completed both culverts to their 180-foot length.
LUBRICATION NOT REQUIRED
Pipe ramming on this job was repeatedly interrupted, not only to deal with complications such as cutting away obstacles by hand, but to give the crew time off for rest and to take weekend and holiday breaks. One concern was that the ground would seize the pipe after a period of inactivity. Yet each time HURK resumed operations after a brief period, the pipe moved without any hesitation.
Pollock rigged up the lubrication system lines and had a lubrication mix ready to use on the first pipe, but he never had to inject the mix. “The wet conditions were sufficiently lubricating the pipe,” he says. So after the first length was installed, he did not rig up a lubrication system on the others.
After installing the two culverts, the HURK crew back-grouted the failed 48-inch culvert, and restored the working pit and tracks from vehicle and equipment transportation. The project was completed in February 2014.
SAVINGS, PRESENT AND FUTURE
Although the obstacles HURK encountered doubled the time it took to complete the installation project, Pollock says an open-cut installation would still have cost the project owner many times over what the pipe ramming operation entailed. Additionally, open cutting would have required closing this section of the line to rail traffic, adding the expense of rerouting cargo and preventing revenue from this line for an extended period.
Further, railbed restoration after an open-cut operation is vulnerable to settling and consequent subsidence over time, requiring future maintenance and additional cost to repair the berm and railbed at a later date.
In contrast, Pollock says, using the pipe ramming method permitted rail service to continue unimpeded throughout the entire four-month project. The ground conditions of the berm and the integrity of the overlying roadbed were never disturbed. They are not subject to further settling.