Trenchless Technology

Feb 1998

Feature

Cable Contractor Tests
Duct Alternative

by Bob Green

Jim Chamberlin was interested when one of his suppliers told him about a "stick pipe" for boring applications that one of their manufacturers was developing. Jim, or "Jimmy" as his crewmembers call him, has been involved in directional boring with Miller Cable since 1979. Miller Cable, based out of Green Springs, Ohio, is the largest heavy highway electrical contractor in Ohio with jobs ranging across the nation. For horizontal boring projects they have two machines. The small machine has an 8000lbs pull back capacity and the larger unit has 20,000 lbs capacity. Jimmy has overseen hundreds of horizontal drilling projects over the years. Duct on a reel is the standard product used, but there have been many situations where site limitations or bad terrain leave little room for the boring machine and a large reel trailer is out of the question. In those applications he has been forced to use a Sch. 80 conduit and uses what he refers to as the "glue and screw" method. They will pre-treat and then heavily glue the PVC to insure a good bond, and then use a cordless drill and screw in several set screws. This method also takes several hours for the glue to cure before the pull can be attempted and there has to be enough area to lay out the assembled pipe. It's obviously not a failsafe method and pull aparts do occur.

Reel duct installation would have been very difficult on this steep slope of an interstate highway intersection. Hasselbach & Associates is based out of Cincinnatti, Ohio and they have the supply contract with the Ohio D.O.T.

Their rep was discussing with Mr. Chamberlin how one of the manufacturers they represented was currently experimenting with a new joint system that would hold pull apart forces much greater than the "glue and screw" method. The manufacturer, Carlon (CTS), is continually looking for ways to improve their products. For several months their engineers have been experimenting with a new joint concept that promises a significant enhancement in pull apart resistance on their "Bore-Gard" product. Armed with only a few details, Jimmy's interest was piqued enough to seek out and call the CTS technical center in Cleveland. He got through to one of the engineers involved in the project and became convinced through their brief conversation that the new concept would work. A short time later he mentioned the product to his contact at the D.O.T. and expressed his feelings about it. Trusting Mr. Chamberlin's judgement, the D.O.T. gave Miller Cable the green light to field trial it.

In November 1997, Miller Cable got the opportunity to join with CTS engineers in field-trialing the Bore-Gard in real world conditions. The installation was in Northeast Ohio at the intersection of routes 271 and 480. There were dual lanes and heavy traffic. It would have been extremely difficult to use duct on a reel due to the fact that there was a very steep slope on the far side. This would definitely have been a "glue and screw" application for Miller Cable. The length of the bore was moderate and the soil conditions were good for the most part. There were large chunks of concrete that had to be worked around and through. After the bore head exited the ground 220' from the machine, the backreamer and swivel were attached to the rod and the first piece of pipe. With the rest of the crew looking on, two men started assembling the first joint. The concept was very simple. From a short distance, the casual observer wouldn't be able to distinguish the "Bore-Gard" from any bell and spigot Schedule 40 PVC. The most obvious difference is a shallow groove cut into the spigot end of the pipe and a matching groove cut into the inside of the bell. Looking inside the bell, the observer will also notice a rubber seal at the end of the bell that reportedly holds up to 75 psi. This feature will enable the blowing of missiles for the subsequent pulling of innerducts. It also seals out any groundwater, protecting the copper or fiber optic cable inside the Bore Gard pipe. Another curious difference is a slanted hole that is cut into the bell where the groove is.

Here's the concept, slide the two pieces of pipe together making sure the grooves are lined up. Take what appears to be a long piece of nylon strip (similar to a large plastic tie strap), push it down through the slanted hole all the way until it stops and it's ready to go.

Jimmy recalls, "Each joint took about a minute because it was prototype material and we had to work it a little bit more to get it started. When the finished product comes out, it should only take an experienced installer seconds to complete each joint." The pull-back was very smooth and went without a hitch. A second bore was then made and connections went a little faster this time. When the assembled pipe was pulled back through, it worked perfectly. An exuberant Jim Chamberlin grinned and told the CTS techs, "You guys got something here! It's what I would call contractor friendly and I'd recommend this product."

Due to the fact that the underground environment is so variable, sometimes it requires that extra bit of effort to find just the right tools to make the job successful and profitable. That's a lesson Jimmy has learned well over the years.