Slick-Boring Installation of 12-Inch Gas Line Under Railroad Tracks

November 11, 2019

120 Feet of Gas Line Installed Under Live Rail by Slick-Boring Despite Multiple Undocumented Obstacles Under the Tracks

To casual observers, modern railroad tracks appear to be nothing more than steel rails nailed to wooden crossties in the ground. However, below the rails and crossties lie carefully constructed systems providing stability and support for the massive loads of passing trains designed to efficiently disperse the forces into the subgrade.

Excavating through the formation completely stops all rail traffic on that section from project start to end. It also compromises the integrity of the formation, posing the threat of eventual, catastrophic failure causing train derailment.

That’s why railroad companies generally permit only trenchless installation methods, trusting the work to specialists like Kinnan Engineering, Inc. of Camas Valley, Oregon. Keith and Diana Kinnan founded Kinnan Engineering Inc. in 1995 as a separate contracting service from Kinnan Engineering’s Underground Technologies division, an underground technologies tooling manufacturer at that time. Utility installations are a Kinnan specialty they offer customers throughout their nine-state, West Coast service area, which includes Alaska.

A 2018 job for a Kinnan utilities customer required the installation of 120 feet of 12-inch-diameter gas line 6 to 7 feet beneath parallel tracks in the SODO district of Seattle. SODO is a unique mix of recreational areas, stores, restaurants and entertainment venues amid office and industrial complexes.

Don Carter, who heads up Kinnan Engineering’s jack-in-bore and pipe-ramming operations, said at first this job had seemed to be a routine installation. Kinnan has done hundreds of railroad crossings over the years, many of larger diameter and greater distances.

Kinnan engineering is expert in all trenchless technologies, and Carter said railway companies most often let Kinnan decide which trenchless method to use, so long as they meet the railway’s stringent job requirements. In ground conditions conducive to boring, Kinnan will auger in the lines. But when there are running sands, such as this one, they employ pipe ramming techniques. Once in a while a railway will even specify a job be done using only the pipe ramming method.

“We’ve been doing pipe ramming many, many years and own an array of equipment from the top manufacturers,” Carter said. “We even use a hammer now in combination with our auger-boring jobs. Right now, in fact, we have a 10-inch hammer on a drilling job, both hammering in and pulling with it.”

Carter said he especially likes the 10-inch ramming tool made by HammerHead Trenchless. “That thing hits hard,” he said. And he likes working with Cameron Zoucha of Ditch Witch West, his trenchless dealer, and with Jim Moore, HammerHead Regional Manager, Rehab and Replacement. “They’re all great to work with. We can call up Cameron or Jim anytime we need something. They respond right away.”

On this 12-inch-diameter Seattle installation, Kinnan used a 12-inch HammerHead ramming tool in a technique called “slick boring.” The technique consists of first ramming a dummy pipe the same diameter as the gas line product from one side to the other. They weld the gas line to the rammed pipe’s end. As they extract the dummy pipe from the hole, the new gas line simultaneously slides into its place. Throughout the process, the bore hole’s walls are held intact by pipe.

This job’s first complication was permitting. Carter said the project’s start had been delayed three times while waiting for the okay to begin, with all equipment and personnel on the site ready to go. 

Project foreman Israel Wafer said another complicating factor was the restricted daily work window due to particularly heavy railway traffic and vehicular congestion. Commuter traffic flows in downtown Seattle are particularly heavy in the morning and afternoon. Therefore, operations could not start before 9:00 a.m. and must cease for afternoon traffic by 3:00 p.m. each day. 

All locates had been done in advance. When permitting came through, with no apparent obstructions or utilities in the bore path, Kinnan dug a 30-foot-long, 8-foot-wide working pit at a depth of about 7 feet and set up standard certified 20-foot steel shoring boxes with standard certified 8-foot spreaders. It was all the room needed to accommodate the 8-foot-long, 12-inch HammerHead ramming tool and the 20-foot lengths of casing.

The first two sticks went in without a problem, Carter said. Each took just 8 to 10 minutes to drive. Time between the sticks to weld the second one on, reattach the hammer and continue driving casing took less than an hour.

While driving the third length of pipe, the casing stopped advancing. It was recoiling with each impact. The abrupt change in sound indicated the pipe was hitting something other than the soils they had been ramming through.

The crew stopped operations to investigate the obstacle. They removed the ramming tool and gear, set their boring machine on the ramming tool’s guide rails and augered spoil from the pipe. When they sent a camera to the other end, they discovered they had struck a wooden pier dead center. They determined it to be the buried remnant of a trestle.

Kinnan met with the general contractor, the railway and the utility owner, their customer, to discuss the three ways they could proceed. They could offset the bore path and begin with the 12-inch casing again 6 to 8 inches to the side. Or they could swallow the 12-inch casing with a 36-inch pipe, which would be able to punch right through the wooden pier. Another option would be to fabricate a tool to cut the wooden pier out of the casing’s path, then continue ramming operations.

Future construction plans required the line’s path to remain as specified. The owner and general contractor favored cutting away the pier to continue on as planned. Carter and Wafer modified a standard rock-cutting head to make it an efficient wood-cutting tool for their augering machine. The tool’s design included the ability to expand once it exited the 12-inch casing and retract again to facilitate its retrieval. It worked perfectly, cutting a hole wide-enough to permit the casing to easily pass through. They backed the tool out of the casing and resumed pipe ramming operations.

Not long after they had started, they ran into a second pier. Once again, they pulled the ramming tool away and repeated the cutting process.   

When they resumed pipe ramming operations for the third time, advancing the pipe to 80 feet, they were stopped again. This time the sounds coming from pipe were different than before. They backed away the ramming tool and collet once again to set their auger on the rails, remove spoil from the casing and send a video camera down to inspect the obstacle. This time the hole was blocked by a discarded man hole cover. Not far from it, they learned, was an abandoned, reinforced-cement manhole.

If they were to stay on the specified bore path, the only option left to them was to dig the manhole out. They had advanced the pipe clear of the track above it by 15 inches, but the railway would not permit them to excavate through the bed’s formation.

That left just one alternative. Kinnan must offset the bore path and begin again, staying as close as possible to the original specification. They left the 12-inch casing in place, filled it with grout, and moved ramming operations two feet to the side to miss the steel obstruction and the wooden piers. As an extra precaution to avoid a submerged pipe associated with the abandoned manhole, they modified their pit, giving it a downward grade of 3 percent.

Kinnan crews sent the dummy pipe across this time without any issues. They pulled the pipe back using their auger-boring machine, completing the gas line installation for their customer in spite of the repeated complications, entirely within the daily work window and without ever interrupting railway or commuter traffic.  

It isn’t the first time Kinnan has found hidden surprises beneath the tracks, many posing daunting obstacles for those less familiar with railroad applications. Trenchless pipe installers around the country have found everything from discarded appliances to entire buried boxcars. “You just never know what you’ll find beneath tracks,” Carter said.

Mike Walk, a pipe-ramming application expert with HammerHead Trenchless, said even the use of ground-penetrating radar (GPR) cannot adequately identify whether an object in the pipe path would stop a pipe-ramming operation. Nor is it a common practice to employ GPR in railway crossing jobs. Walk said, “There really is only one way,” Walk said. “You do exactly what this contractor did. You clean out the pipe and then send a camera, or in larger diameter installations, a person, to visually identify the object.”

Regardless of the preliminary documentation they receive and their own routine exploration of a planned bore path, trenchless pipe installers around the country have found everything from discarded appliances to entire buried boxcars. While these may pose daunting obstacles for those less familiar with railroad applications, in over 20 years of trenchless installation, the obstacles that Kinnan crews have encountered have never resulted in failure to complete an installation.

Carter said that Kinnan may indeed one day encounter subsurface obstacles that may prove impossible to overcome. However, he is confident that any pipe-installation contractor competent in a wide variety of trenchless methods and using quality equipment matched to the specific job will find a way to complete almost any pipe- ramming project in spite of surprises hidden in the formation. Experience and capability of on-the-spot innovation boost expectations of success.