Preventing Underground Damage

Construction professionals understand the importance of not damaging buried utilities while performing any type of new construction and maintenance work. Even so, accidental strikes of underground utility lines continue to interrupt essential services, cause millions of dollars in damage, result in serious injuries, and in some cases, loss of life.

As utility easements become more crowded, preventing damage to underground facilities has become increasingly challenging. “Protecting our buried utilities is of critical importance,” says Mike Dvorak, Sales Manager – Electronics for The Charles Machine Works, Inc. “Utility damage prevention is a responsibility that involves many diverse public and private organizations, making communication and cooperation essential to reduce the number of underground utility strikes.”

First Step
The first step in preventing damage to buried facilities is to accurately locate and mark all utilities in a work area before construction. This process is initiated with a call to the local one-call center, providing the exact location of the work site and requesting locates be made. The call must be placed at least 48 hours before work is scheduled to begin.
The one-call center then contacts appropriate utility providers, who then locate and accurately mark positions of buried lines. Some utilities use their own personnel; others employ contract-locating specialists.
The basic tool used by locating personnel is the electronic locator, which consists of a lightweight hand-held receiver and compact transmitter unit. It is designed to help make locating buried cable and pipe easier and to provide more accurate results. Some units, like the 950 receiver and transmitter from Ditch Witch Electronics, use different frequencies and modes to find locations of different types of utilities by detecting magnetic fields created by electrical current passing through the lines.
In some situations, the receiving unit is all that is necessary to locate electrical and television cable signals. To find telephone cable and metallic pipe, the transmitter unit is connected to cable or pipe and a current is sent through the line, creating a signal that is detected by the receiver. For PVC pipe with tracer wire, the wire is energized by the transmitter to provide a signal that the receiver can read. The receiver processes information and displays an estimate of depth and other data on an easy-to-read screen.
Dvorak says that some utilities also mark positions of buried facilities with 3M electronic markers, which are buried with pipe or cable. Markers are passive resonate circuits with no internal power source to run down; their polyethylene shells are impervious to minerals, chemicals, and temperature extremes. They are located using a Subsite 950 Receiver equipped with an Electronic Marker Locator (EML) attachment that transmits a signal to the buried marker, which resonates it back to the EML.
“Ground-penetrating radar technology also has been adapted for utility locating purposes,” Dvorak notes. “For example, our 2150 GR Ground Penetrating Radar (GPR) can be used to detect and locate both metallic and non-metallic pipes and cables, but the method is dependent on soil conditions and antenna selection. GPR products are not effective in all types of soils, but can be helpful in locating some previously unknown facilities.
“Potholing, physically uncovering a buried utility to confirm its location, is the surest method of determining its exact position,” Dvorak continues. “Because of accelerated efforts to prevent damage to buried utilities, potholing is becoming a standard practice on a growing number of utility jobs. Government agencies are adopting regulations that require potholing, and project owners and contractors are establishing their own policies specifying potholing before excavation or directional drilling begins.”
While this procedure isn’t new, until recently potholes were dug with backhoes, and even skilled operators alwaysran the risk of hitting and damaging the pipe or cable they were attempting to locate.

Soft Excavation
Soft excavation has changed all that, Dvorak points out. “Portable vacuum excavators use high-pressure water or air to quickly dig small, precisely controlled potholes to uncover buried utilities,” he says. “A vacuum excavator uncovers buried pipe or cable without the risk of damage inherent with a backhoe, excavator, or other mechanical tool.”
The Ditch Witch FX60, for example, uses a high-pressure stream of water, precisely directed by a hand-held wand, to displace soil. Depending on soil conditions, a 12-inch-square, 5-foot-deep pothole can be completed in less than 30 minutes.
“Vacuum excavators,” says Dvorak, “are capable of digging much deeper, but utility potholes seldom need to be more than six feet deep. The vacuum function of the dual-purpose machine picks up soil displaced during excavation to use later as fill or to be removed from the job site. Soft excavation causes less surface damage and reduces disruption of traffic and other surface activities. The small excavation is easier, faster, and less expensive to repair.”
For many utilities and contractors, potholing is standard procedure on horizontal directional drilling projects when the path of a planned pilot bore either crosses or is in close proximity to buried lines. “A vacuum excavator’s usefulness isn’t limited to HDD operations,” adds Dvorak. “It is the ideal tool any time a small, carefully-controlled excavation is necessary. Vacuum excavators also are used to clean up drilling fluids that escape from bore holes during drilling, backreaming, and product installation and can be used as a powerful, portable vacuum for just about any type of clean-up need.”

Best Practices
The Common Ground Alliance (CGA) efforts focus on implementing best-practice procedures identified in the Common Ground Best Practices Study, recognized as the most effective guidelines yet developed for preventing damage to underground facilities. One of CGA’s primary roles is coordinating information and communications among the various organizations involved in building, maintaining, and operating the utility infrastructure.
“CGA,” says Dvorak, “encourages the shared responsibility of utility damage prevention and helps achieve this by refining and disseminating best practice recommendations, developing public awareness through educational programs, supporting appropriate research, and serving as an information clearinghouse.”
A “Dig Safely” public awareness campaign, including a damage-prevention brochure and video, and the “Call 811” initiative are in progress to make construction personnel and the general public aware of the importance of notifying one-call centers before construction begins.
More information on CGA programs is available at www.commongroundalliance.com. iP

video