Ground Penetrating Radar – GPR Service

• Ground Penetrating Radar – GPR

Ground penetrating radar is an instrument used for detecting subsurface anomalies. It is a piece of equipment that is pushed / pulled over the ground inducing pulses of electromagnetic energy into the ground, which in turn reflects off subsurface features. The depth in which the GPR can detect services is primarily down to the soil conditions in your proposed work zone (sand and dry soil produce better results and condensed wet clay). The GPR can detect under tarmac, concrete, various soil types and is self-calibrating to suit the sub surface conditions you are scanning. It can be used to detect gas, water, oil, foul and surface water pipelines, electrical cables and ducts. GPR is also capable of detecting rebar in concrete slabs, caves, graves, voids, walls, subsurface streams, tanks, trenches, and soak wells. The use and interpretation of GPR is greatly down to the experience of the operators. Metroscan can offer clients GPR Technicians with 20+ years’ experience in the industry.

• Electromagnetic Locating Device – Cat & Genny

Electromagnetic Locating Devices or the Cat and Genny as it is better known to most, is a standard piece of equipment used for tracing conductible underground services. It consists of two parts, the transmitter (generator) and the receiver (Cat – Cable Avoidance Tool). The transmitter omits a selected frequency into the nominated cable or pipe, which can then be detected by the receiver. This enables the operator to locate the nominated cable accurately, horizontally and vertically. Depths are accurate to +10% of the depth of the service.

Cat and Genny Locating Methods

The 3 common uses of the cat and genny are Direct Connection, Signal Clamping and Induction:

1. Direct Connection – This is the preferred and most accurate method used for locating underground services. However, to apply this method you require a direct connection to the service eg. Valve, earth rod. The transmitter is then placed next to the point of contact. A double connection lead from the transmitter is connected to the point of contact, whilst the other lead is earthed. This sends a signal though the cable which can then be located with the receiver.
2. Signal Clamping – This method is similar to the Direct Connection, only it is utilised where there is no direct point of contact to the service. A ring clamp is placed around the cable or duct, which is connected to the transmitter, sending a signal down the cable.
3. Induction – Induction method is used when there is no visible point of access to the cable or pipe you are required to locate. The transmitter is placed above where the said cable or pipe is thought to be. A signal is induced into the ground and subsequently into the cable. The service can then be traced using the receiver. This is the least favorable method of locating as the signal can bleed off to other nearby services.

Other uses of the Cat and Genny are the passive and power modes. These modes are generally used to locate unknown or undocumented conductible services in the proposed work zone.

• Metal Detector

Metroscan utilise metal detectors on site to assist in Locating buried manhole covers, valves, hydrants and often steel / metal tanks.

• Global Positioning Systems (GPS)

When all underground services have accurately marked and identified on site, the coordinates of these services are recorded using the most up to date GPS technology. This in turn is placed on a CAD file for the client and presented in 2D, 3D or PDF format. Results can be overlaid on a topographical survey of the site. GPS coordinates of all located services can be readily obtained from Metroscan on request.