Among the longest-established trenchless installation methods is the use of pneumatic piercing tools: an option that has been providing contractors with a cost-effective and easy-to-use alternative to trenching for nearly half a century. Water, gas, sewer and electrical interests have all benefited from this established and proven underground method, which also serves as an efficient alternative to larger directional drilling equipment. As is the case with nearly every installation approach, piercing tools are most effective when used in specific situations.
“We started using piercing tools more than a decade ago because of the flexibility they provide,” says Del Dixon, project manager of United Cable Construction, based in Ladson, SC. “Piercing tools is ideal in situations where there is limited access and in tight spaces. One of the biggest advantages is that piercing tools don’t require a very large launch pit for operation.”
United Cable, which has been in business since the early 1980s, specializes in underground utility installations of all types, including trenching, plowing, horizontal directional drilling (HDD) and the aforementioned pneumatic piercing tool method. The company has completed projects in many East Coast states, although they like to focus on jobs originating close to home in the Carolinas and Virginia. According to Dixon, the various soil types most prevalent in their primary trade territory are ideal for employing piercing tools as are the types of installations United Cable has become so proficient in completing.
The company recently expanded its arsenal of underground installation equipment with the addition of the Vermeer Hole Hammer pneumatic piercing tool, manufactured by McLaughlin, based in Greenville, SC.
“With the soil types we have in this area, and the types of installs we prefer, the use of piercing tools is an efficient and effective solution,” Dixon says. “It’s been our experience that piercing tools are a relatively low-cost approach for completing shorter bores, especially in highly congested areas with an already well-established underground infrastructure. It is also a very productive method. Depending on bore sizes, we’ve been able to use just one compressor to power up to three tools at a time.”
Recently, underground installation experts with United Cable traveled to Mooresville, NC, located just a short distance north of Charlotte, the state’s most populous city. More commonly known as Race City USA, Mooresville is home to more than 60 NASCAR teams and several racing-related businesses, including two automotive museums. The reason for their visit, however, had little to do with racing, aside from the fact that most likely due to the popularity of the sport, Mooresville is experiencing a population boom.
Fiber Technologies tapped United Cable to complete an intricate two-mile fiber installation project to bring an additional cable and Internet service option to Mooresville residents. The installation plan for the project specified CIC feeder cable, approximately half an inch in diameter, encased by a 1¼-inch outer conduit — both coaxial and fiber optic — be installed.
Dixon, who served as project manager on the Mooresville job, selected pneumatic piercing tools to complete the bulk of the installation, occasionally relying on a small tractor equipped with a cable plow in areas where existing infrastructure wasn’t a factor. Installation easement was specified on the street side (front) of each lot, so concern for disruption, footprint and maintaining the integrity of existing landscaping was a primary concern.
“The Mooresville job was ideal for using a stitch boring installation approach since there were multiple shots using piercing tools,” Dixon says. “The site was an established residential area where several utilities had already been installed so the infrastructure was already crowded. That’s what’s nice about using pneumatic piercing tools; it gives you an opportunity to locate existing utilities. We spot existing utilities when self-excavating our launch pit. That way, we can accomplish two things at the same time.”
Stitch saves time
The stitch boring approach is fairly common when using piercing tools, especially on sites where an already crowded utility infrastructure exists. Basically, stitch boring is characterized by a series of multiple shorter shots — usually less than 50 feet in length — at fairly shallow depths. On the Mooresville job, Dixon’s crews used a 2½-inch chisel head to install the encased feeder cable at depths of 24-inches for the coaxial cable specified for residential neighborhoods, and 36-inches for fiber optic lines as outlined in the installation plan.
Careful consideration to minimize footprint and disruption to property while maintaining the integrity of individual homeowner yards and landscaping was a given by Dixon and his crew when preparing the launch pits — each approximately 4½feet deep and 18-inches wide — required to complete the installation. This includes using tarps for temporary storage of spoil, cutting sod for surface reinstatement and expediting completion within the same day so as not to disrupt homeowners any longer than necessary — all of which Dixon refers to as jobsite best practices.
“Generally speaking, existing utilities will determine where launch pits are situated,” Dixon says. “The Mooresville subdivisions were already well established. Most had gas and water services, along with sewer taps coming from the house. I’d estimate we were digging a launch pit every 30 to 40-feet. Typically, using piercing tools, a 40 to 50-foot shot is ideal which is about what we were able to accomplish on the Mooresville project.
“We’ve completed longer shots before, but doing so is really not the ideal approach,” says Dixon. “The farther you shoot a tool, the more things come into play. For example, if the direction is off ever so slightly to begin with, the longer the bore, the greater the tendency for the tool to stray, even rise up in elevation, especially if the head confronts an obstruction.”
In just one simple step, the piercing tool completed each bore and then pulled the fiber in behind it — a one-step process that helps to enhance overall installation productivity and is both accurate and cost-efficient. Contrary to most contractors that typically employ five- and six-man crews on a site, Dixon prefers a four-man approach.
“Inevitably when you send five or six men out on a project, one or two guys end up standing and watching with little, if anything, to do. We’ve found that using four-man crews helps keep labor costs in line,” Dixon says.
Helping to keep crew sizes lower are some of the features of the newer piercing tools. According to Jeff Wage, vice president, sales and marketing for McLaughlin, the Hole Hammer piercing tool has been engineered with a number of innovative features that help provide better control and easy start-up.
“The moving-head design of the Hole Hammer piercing tool provides full striking force of the piston to the head of the tool,” says Wage. “This helps the tool pulverize any stone or debris in its path, while the residual energy generated is used to help the tool body travel through the compacted bore path. The design helps improve accuracy in tough soil conditions and reduce tool deflection. The Hole Hammer also has a mechanical reset for the head assembly that helps to ensure that each blow actually compacts the soil in front of the tool; another feature that helps with accuracy.”
Expectations by Dixon are that crew members achieve 400-plus feet of production including excavation, installation and restoration — per day. “Piercing tools continue to be a low-cost trenchless method for installing short bores in congested infrastructure, on a cost-per-foot operation,” he says. “These tools continue to gain footage as the right approach and given the right situation. For the most part, using piercing tools, you can hardly even tell where you’ve been in a subdivision three or four weeks after completing an installation. There are limitations, of course. But given the right situation, piercing tools are often the most cost-effective and least invasive way to go.”
FOR MORE INFO:
United Cable Construction, (843) 851-0711
McLaughlin Group, (800) 435-9340, www.mightymole.com
Vermeer Corp., (888) 837-6337, www.vermeer.com