When undertaking a survey for buried utilities, one of the most important things is to have STATS – site plans – available. Unfortunately, the CAT and Genny are not infallible, but the more information a surveyor has on site the better chance he/she has of investigating all the possibilities. For example, if there is no signal, no marker posts, and no access points, and the service is buried out of sight, there is no way of knowing that it is there. Having records, even thought they should not be relied upon on their own, can help to identify any services that might possibly be present.

The two main pieces of equipment used for underground surveys are the CAT 4 and the Genny. At Sygma Solutions our training courses teach surveyors how to use both in combination in order to have the best chance of success in locating and identifying underground services. Among other tools, our Radiaodetection CAT 4 training is second to none, and we also provide training in the use of the Mala GPR equipment.

The RD8100 precision locator works on electromagnetic principles and is used for locating metal pipes and cables and any other services that employ metals. The RD8100 has a passive method and an induction method and can also be used in direct connection mode. In passive mode the RD8100 locates buried service such as electricity cables or telecoms which give off their own background signals automatically. As long as the signal is strong enough it can be located at the surface.

However, if there is no power running through the cable and it is effectively “switched off” there will be no signal. A classic example of this is street lighting. During the day when the lights are off there will be no signal. Unfortunately, this means that if one relies on the RD8100 in passive mode only and assumes that there is nothing there, then if workers were digging late in the afternoon in the winter they could very easily strike a live cable that the survey said did not exist!

However, there can still be problems with live cables. Some high voltage cables are the “balanced” type and are specifically designed so that they do not emit a signal, and it doesn’t matter if they are 11Kv or 33Kv: if that is the way they are designed, then they cannot be detected by the passive method.

There can also be issues with certain types of ductile pipe because while certain small sections of pipe may be able to be traced, some of them have a rubber seal at the end of each pipe segment and this breaks the conductivity of the signal.

The RD8100 can then be switched into induction mode with the object of generating a signal on to a target utility and tracing the generated signal at the surface. The generator is place on the ground and a signal generated into the ground in order to “attach” itself to a buried service and travel along its’ length. That signal can then be detected at the surface.

However, this is not always successful, and it means that the signal generator must then be physically attached to the utility using clip leads or a clamp. In turn, this means that there has to be access to the utility at some point so that the generator can be connected, and this would usually be via a cable riser, an inspection chamber, stop valve, or plant room. Unfortunately, an access point may not appear in the survey area or could even be behind locked gates, and this is another reason why STATS can be useful in giving an idea where access points could be.

If it is not possible to locate a service using the RD8100, then one can turn to the Mala GPR. This does not physically locate buried services but seeks out differences in the ground density which can indicate where services run. However, this too can have problems since the radar unit needs to be very close to the ground, and if the surface is bumpy and uneven it can cause problems. There can also be issues if the ground is very wet, or heavy clay soil, or there is lots of rubble that has been backfilled, all of which can disturb the signal.

So you can readily see that there is far more to learning how to use these tools than just getting them out of the box and reading the instructions, which is why you need to take one of our courses at Sygma Solutions in order to become fully up to speed.