Utility mapping is a crucial part of the process when preparing ground works, especially in areas where there are known electricity, gas, water or telecommunication conduits whose precise position is not known. Landowners who have existing lease for cell towers may consider a cell tower lease buyout from companies who would like to use the telecommunication facilities.
Mapping what is beneath the surface of the ground provides peace of mind when disrupting the earth, as well as preventing potentially dangerous situations such as gas and water leaks, or digging into a live electrical cable. To determine if there are water leaks, liner integrity testing is usually conducted.
However, the different utilities present their own challenges, and with a variety of utility mapping equipment to choose between, how do you know which tool to use, and which to leave in the van?
We spoke to utility mapping experts, City Surveys & Monitoring, to find out more.
CAT – Cable Avoidance Tools
A Cable Avoidance Tool, or CAT, is your first port of call when scanning for electrical supplies below ground, but even here there are several things to take into consideration.
Modern CATs can offer an estimate of how deep an object is, along with its lateral position, and this is essential to help identify hazards that lurk only just below the surface, as well as eliminating concerns about pipework if it is well below the maximum depth you need to dig to.
You can also get CATs that operate on extra frequencies in addition to the industry standard 8 kHz and 33 kHz; these additional frequencies can allow for much longer-range measurements, ideal for larger sites and work on roads and motorways.
Genny – Signal Generators
To use a CAT properly, you also need a signal generator, commonly known as a Genny. Without this, the CAT can only detect live electrical cables – and not cables that are not currently passing current, or other utilities.
With a Genny, a signal is passed through water pipes, telecoms wires, and plastic or clay pipes, along with other materials, allowing them to be picked up by the CAT.
Again, a Genny capable of emitting those extra frequencies can enable detection over a larger range, but to do so you must make sure that both your Genny and your CAT are capable of operating on the same additional frequencies.
GPR – Ground Penetrating Radar
Ground Penetrating Radar, or GPR, is the technology made famous by the ‘geophysics’ team on Channel 4’s archaeology show Time Team, and is capable of detecting underground anomalies regardless of whether or not a current is present.
This might make it sound like the obvious first option, as it can map physical features below ground without the use of a Genny.
However, the data obtained can be less precise – more of a general idea of an object’s size and position, rather than an exact image of where it is – and this makes the ‘CAT and Genny’ approach preferable for materials that can be detected in that way, especially including live cables and metallic pipes and conduits.
What equipment should I use?
As always, the best tool to use is the right one for the job – and there are times when GPR will be able to detect objects that a CAT might not, even with a Genny.
However, when the situation allows for either to be used, the combination of CAT and Genny is a good first choice, offering accurate results with good precision and, with modern equipment, a measurement of depth as well as lateral position.
There are benefits to using a CAT and Genny even on live conducting cables, too, as the Genny’s signal can be passed without interrupting the electricity supply.
In this way, the Genny acts as a further backup as well as – and not instead of – detecting the live current of the cable itself, giving an independent secondary verification of the precise position of the utility below the ground, for complete confidence in the data.
