Tools used in Underground Utility Location
PIPE & CABLE LOCATORS
The basic premise behind an underground utility locator is that it works by producing and transmitting a signal onto a utility that is metallic that the receiver can detect. A signal (measured in kHz or Hz) can be produced by a transmitter and is sent through the utility by either conductive or inductive means. “Conductive” means a direct connect connection such as alligator clips. “Inductive” means the signal is “induced” onto the metallic utility line with an induction clamp which is secured or clamped around the utility line but does not connect metal to metal as the conductive alligator clip does. Inductive is great when you don’t have access or ability to do a direct connection. In case you’re wondering, the conductive method is better since it is metal to metal and the transmitter is able to send a signal better. Once your transmitter is connected and turned on producing a signal on the utility, you can then take the receiver part of the instrument and wave it over the areas you believe the utility to be in. When you start picking up the signal you will over time learn how to pin-point exactly where the utility line is buried, and how deep. This takes practice over time but new-comers to the utility location profession can learn it fairly quickly but should be trained by someone with years of experience.
2 Man Inductive Electromagnetic Sweep & 1 Man Split Box Inductive Electromagnetic Sweep
In a 2 man sweep, one person holds the receiver while the other holds the multi-frequency transmitter and they determine where metallic/conductive utility lines are by walking together slowly across the ground and looking for unknown underground lines. An inductive sweep is performed after all known utilities that have above ground evidence have been marked. An inductive sweep can also be performed with a single frequency split-box. Conducting an inductive electromagnetic scan should be performed at the end of every project.
GPR ( Ground Penetrating Radar)
Ground penetrating radar (for utility locating application) is primarily used to locate non-metallic “unlocatable” facilities, underground structures and storage tanks. Ground penetrating radar is a non-destructive, gentle way to locate subsurface utilities. In the right conditions, practitioners can use GPR to detect subsurface objects, changes in material properties, voids and cracks.
Any service that is up to date on best practices for locating items underground should already be using these tools on an everyday basis. Making sure that they do can save you many hours of labor on the final invoice they present you for payment.
Additional Methods for Verifying Underground Utility Locations.
Vacuum excavation services use a high powered air stream to dig faster than the traditional methods. This type of excavation is also safer than using traditional tools like a shovel or excavator because there is no risk of metal hitting metal. The high pressure air stream breaks apart the molecules of dirt and clears the way for the technician to spot any utility lines or underground features that shouldn’t be disturbed. Not only is this method safer, its also cleaner because the vacuum removes any extra dirt before it can pile up.