December 2012, Vol. 67 No. 12
Features
Microtrenching Offers Economical Installation Option
For some time now, horizontal directional drilling (HDD) has been capable of replacing open-cut construction on segments of many projects. The benefits of HDD are well known — it can minimize excavation, dust pollution, and reduce damage to surface improvements which can significantly lower time-consuming and costly restoration of surface damage.
While HDD and other trenchless underground utility construction methods receive heavy coverage in the trade press, little is written about trenching. However, trenching often is the fastest and least-costly method for installing duct and conduit for underground telecommunications and power distribution, particularly in open areas and locations without heavy concentrations of existing buried utilities.
Quanta Services has developed a microtrenching process specifically to install underground duct for fiber optic cable. Since its introduction in 2009, the Quanta Q-Trench Solution has played an increasingly important role in the expansion of broadband networks.
The patent-pending Q-Trench construction technique uses specially-developed equipment to simultaneously cut a trench as narrow as a half-an-inch and 12-inches deep through asphalt while at the same time removing spoil with a vacuum system.
After conduits are placed in the trench, the excavation is filled with a proprietary, environmentally-safe grout that is immune to shrinkage, weathering and erosion.
Although microtrenching equipment and vacuum equipment is available from various sources, Q-Trench is available as a turnkey service only from Quanta Services.
“The Q-Trench solution was the first in the marketplace to cleanly cut and vacuum a sub-inch-wide,12-inch-deep trench in one pass to install conduit for fiber cable,” said Ken Trawick, president of telecommunications and power generation divisions for Quanta. “This patent-pending method of microtrenching eliminates many of the concerns associated with traditional construction methods and it also is less expensive, and nearly eliminates community disruption inherent with other types of construction.”
When it was introduced, Quanta projected the Q-Trench process could cut project timelines in half and reduce costs as much as 75 percent.
Since then, refinement of the process has resulted in even greater savings, said Trawick.
“A project in an area that would have been priced at $20 — 25 per foot, now is approximately $15 per foot,” Trawick continued. “Daily productivity — the number of feet trenched per day — also has increased.”
As 2012 nears an end, more than 500,000 feet of Q-Trench construction has been completed, Trawick emphasized.
The MT55 trencher used in the Q-Trench system is a 60-horsepower, four-wheel drive model with a trench cutting component developed by the Charles Machine Works specifically for use in the Quanta system. The microtrencher component resembles a large circular saw. The MT55’s saw can be offset to enable trenching near curbs and other obstacles. It is equipped with industrial diamond carbide bits to cleanly cut the trench to the project’s exact width and depth specifications.
A vacuum hose from a vacuum excavator is connected to the trenching attachment and removes spoil as the excavation is made, transferring it to a holding tank where it is contained for later disposal.
When conduits have been placed in the trench, Micro Trench Backfill is mixed with water and fills the trench. After curing, an asphalt sealer is mixed with water and fills the trench. After curing, an asphalt sealer is applied. Both the asphalt sealer and backfill were developed for Quanta Services by SuperGrout Products.
When mixed with water, the grout becomes the consistency of milk and is installed by a two-person crew using a simple mixer and application wand. Trawick said the fluidity of the grout allows it to surround the cable track without jeopardizing the integrity of conduit holding the fiber cable. In less than 12 hours, the grout becomes structurally sound, and sealer can be applied. This eliminates the possibility that fiber networks will become exposed in shallow trenches due to erosion and weathering. The grout will not erode, but it is relatively easy to remove should it become necessary to access the conduits.
After the excavation is filled, a cap is applied to the surface.
Trawick said the core process of Quanta’s exclusive microtrenching process has not changed since its introduction, but improvements have been made.
“The most significant enhancement,” he said, “is the asphalt sealer. Quanta has worked with SuperGrout to create a sealer that has more elasticity, yet is denser than its predecessor, and it stands up to more variant temperature swings.”
Microtrenching seldom is the only method used to install underground conduit on a project. Directional drilling and conventional trenching still are used in appropriate circumstances.
“Microtrenching simply is a new and effective construction option,” Trawick said. “The key to microtrenching is knowing when to use it. As in all construction situations, it is important to select the right process for the job. Microtrenching makes the most sense for areas where fiber deployment is not currently cost effective, such as downtown areas and congested neighborhoods.”
Quanta Services is a leading specialized contracting services company, delivering infrastructure solutions for the electric power, natural gas, pipeline and telecommunications industries. The company’s comprehensive services include designing, installing, repairing and maintaining network infrastructure nationwide.
FOR MORE INFO:
Quanta Services Inc., (713) 629-7600, www.quantaservices.com
Ditch Witch, (800) 654-6481, www.ditchwitch.com
Q-Trench On The Job
A recent project illustrates integration of microtrenching into a project.
Construction of a broadband network required installation of 200 miles of underground fiber optic cable with approximately half the conduit installed by the Quanta Services Q-Trench Solution.
On a typical day, three microtrenching crews worked on the project, said Ken Trawick, president of Quanta telecommunications and power generation divisions. Cable routes were in city street rights-of-way and on homeowner association property. Cuts were made parallel to and across streets. Asphalt surfaces range from new to badly-deteriorated asphalt.
“Each crew averaged about 1,500 feet per day,” said Trawick. “Twenty-four hours after the trenches were filled, asphalt mastic was applied on top of the grout-cured trench.
“The benefits of microtrenching for this project were speed of installation, low-impact along rights-of-way in private, upscale residential developments and cost savings compared to traditional construction methods.”
If the Q-Trench system had not been available, Trawick said, rock saw equipment would have been the primary option of construction on segments where microtrenching is being used.
“However,” he added, “rock saws would not have been allowed in many areas because of the dust and dirt they cause during construction and the lengthy cleanup and restoration necessary. On this project, microtrenching certainly showcased its capabilities in high-end areas where residents are very sensitive to construction that is disruptive to their neighborhoods.”
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