Improvements Continue To Drive GPR Applications

By Jeff Griffin, Senior Editor | April 2009 Vol. 64 No. 4
Mala USA's GPR

Issues resulting from accidental damage to underground utilities continue to receive priority in the underground construction industry as initiatives to protect buried facilities gain momentum.

Data from the Common Ground Alliance document indicate that the primary cause of utility strikes is failure to accurately locate and mark buried pipe and cable.

Electronic locators remain the basic tool to find underground facilities, but they have limitations. Hand held electronic receivers detect buried facilities via a signal. Generally, plastic pipes cannot be found unless they are equipped with tracer wire to carry a signal generated by the locator's separate transmitter unit. Communications cable also must be energized for the locator to detect it. Signals from nearby power sources often can interfere with the locator's accuracy.

Ground Penetrating Radar (GPR) offers an alternative.

GPR locators send a signal through the soil which bounces off objects and returns a signal to the unit's receiver providing vertical and horizontal positions with a display of the object on the unit's screen. Tracer wire is unnecessary. Most models are on wheels attached to handlebars similar to a lawn mower, and the operator pushes the device across the ground to locate and view a representation of what's below.

However, GPR also has limits, the most important being that its performance is much less effective in dense soils.

Representatives of key suppliers of GPR locators and one firm that offers geophysical services that include the use of proprietary GPR locating equipment, discussed information about GPR locating technology with Underground Construction.

Mala USA, Vincent Ferrara, Senior Account Manager: The primary advantage of GPR is that it detects not only metal pipes but all types of material. A tracer wire is not needed to direct connect to any utility. Sometimes GPR is the only solution for finding nonmetallic utilities without a tracer wire in dry, sandy soil. By pushing the GPR system across the surface of the soil, the unit provides a readout of the subsurface. On the GPR screen, the operator sees a hyperbolic indication of the buried utility with accurate horizontal and vertical positioning. The closest and simplest analogy is an image similar to that of a fish finder.

The latest GPR systems for utility locating are more compact, easier to use and affordable than anything previously produced.