Equipment

RD8000 – CAT – Radio Detection Cable Locator

The cable detector is a hand held instrument that can detect a broad range of frequencies, indicating underground electrical cables and telecommunication cables. Using the instrument the survey area is crossed in a grid pattern and any live cable mapped using the instrument display and tone generated as an indication. The instrument picks up detected services at a 90° angle, giving an indication in which direction the detected services are aligned.

Non-load bearing metallic services or cable can be picked up making use a signal generator. Direct use of the signal transmitter entails the clamping of the services that need to be surveyed onto the signal transmitter. The signal generator then induces a signal directly into the conducting service, making it possible to track the route of the underground service.

When using the signal transmitter indirectly, the operator broadcasts a signal into the ground. This induces frequencies on services with the capability of conducting the signal. Using the cable detection instrument, these services can be located if they resonate or carry the broadcast signal. It is however important that a starting point for the service can be located.

The RD8000 system provides cable and pipeline locators with a fast, effective means of locating and mapping buried utilities.

The RD8000 makes use of the RF signals generated in live electrical cables or phone cables.

A signal generator is clamped to an identified conductive service and the induced signal can be tracked along the length of the service.

A signal can also be induced using an indirect broadcast from the signal generator.

Information that can be collected

  • Location of the service
  • Depth to the top of the service within 10%
  • Other information gained through investigation of manholes, or access points
  • Services located closely together or conduits cannot always be distinguished, but are marked as bands of services

GSSI – GPR – Ground Penetrating Radar

Ground penetrating radar (GPR) is a geophysical method that uses radar pulses to image the subsurface. This non-destructive method uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum and detects the reflected signals from subsurface structures. GPR can be used in a variety of media, including rock, soil, ice, fresh water, pavements and structures. It can detect objects,  changes in material, voids and cracks.

The GPR unit used is a SIR-3000 model with a rugged cart manufactured by GSSI. The cart is pushed along the investigation area in a grid or target pattern. It is critical that the antenna is in direct contact with the ground surface and as such the GPR can only be used on reasonably level areas. Paving or concrete can be penetrated unless it is has been highly compacted or contains a significant amount of reinforcing steel.

Information that can be collected

  • Location of the service
  • Depth to the top of the service within 10%
  • The size of the service can be gauged to some extent based on the parabola indicated
  • Other information gained through investigation of manholes, or access points
  • Services located closely together or conduits cannot always be distinguished, but are marked as bands of services

Underground Detection Essentials

  • Underground service detection can serve as a tool to avoid the risks of damaging services during refurbishment activities
  • A tool to re-map and re-create as built plans based on the real location of services
  • It can be used as a risk management tool and to provide information for other activities
  • Important to note that geophysics still is an inferred approach and that 100% accuracy and risk control can still only be achieved with trial excavation
  • Hand excavation or air lancing is always recommended prior to work in the vicinity of identified services
View Limitations

Underground Detection Equipment Limitations

  • Ground penetrating radar does has limited penetration through very dense compacted material, saturated soil or soils covered in reinforced concrete
  • Where the dielectric value of the surrounding soil and the service you are looking for are close to each other, a very weak or no reflection will be visible
  • The GPR unit has to be in contact with the soil surface and irregular surfaces cannot be scanned
  • Outside interference from high voltage underground or overhead lines
  • Detected underground services cannot always be service-specifically identified unless they are visible at a termination point, manhole or according to existing information
  • In areas where underground services are densely concentrated in sub-metre areas, services will be indicated as a band of services. Equipment used in the proposed survey can’t distinguish between individual services in such areas if ground conditions do not allow it
  • Services buried on top of each other can often not be distinguished using electrical or radar detection methodologies
  • Depth of detected services can be supplied by the avoidance tool if a good signal connection can be made or by GPR within a 10% accuracy
  • Dense clay formations, high water tables, rubble used as backfill, excessive steel reinforcement in concrete or even load shedding can influence the accuracy of the equipment used and the outcome of the survey
  • Whilst employing appropriate equipment, processes and best endeavors at all times, no guarantee can be made that any particular element of buried infrastructure will be properly detected or parameterized by the proposed survey due to the large number of variables encountered on different sites. For critical applications it is always recommended that a survey be followed by careful hand excavation and air knife probing