Intermat: mapping of buried, new construction of detectors

1 July 2012 will be a key date for urban contractors. It's that day qu'entrera into force a comprehensive regulatory reform to improve the safety of working near underground networks: building owners and businesses will have an obligation to consult the "Single Window" for contact information for operators on the area they plan to carry out their work. Operators, they have until 1 July 2013 to make the recording of settlement areas of their networks, from 2019, will be georeferenced.
Large mapping work in perspective. Who will do? "There is an urgent need for specialized service providers," says Hubert Brérot, president of the National Federation of Business detection of buried. No doubt young companies will embark on this path. But what hardware they will have?

Acoustic, radio waves or geo-radar

A June 2008 study commissioned by the FNTP are three main methods of detection: acoustic, radio and the geo-radar. Adapted to rigid networks, acoustic methods include vibrating the pipes are broadcasting a sound wave. Its location is then marked by "listening" to the ground. Advantage of the method: it can detect non-metallic networks. Disadvantage: it requires physical access to the pipes to place the speaker and it does not detect networks flexible electric cables for example.

For them, it is better to prefer detection by radio waves. Power cables emit, so they are easily spotted. Cables off or metal pipes act as antennas: even underground, they capture radio waves surrounding and change. It is these variations that the detector sees.

To be more precise the sensor can be coupled to a transmitter. The latter, lying on the ground or directly connected to the pipe, emits at a particular frequency, which simplifies the search and can measure more accurately the depth of a buried utility.

Detect non-metallic networks

The radar is well suited to deep, at least up to 3.50 m. Precision altimetry is plus or minus 5 cm regardless of the medium. However, this technique does not detect non-metallic networks, unless they can introduce a glass fiber probe covered with a wire: it is he who will be identified by the detector. But this requires physical access to the pipeline and that it can receive the probe, which is not the case with a sheath of optical fibers for example. The geo-radar, it allows a priori to detect all types of networks.

Its principle is based on the fact that the speed of propagation of a wave depends on the nature of the material passed through. A wave is emitted, we measure the time of return of its echo. The various obstacles she encounters appear on a screen, but in a little explicit. Only specialists are able to use such devices. It does not meet the needs of men site, which for ease of use and understanding prevail over technical performance. Small equipment suitable, simple and solid, exist.

The Ezidig example: this detector via radio waves clings to the pendulum of a mini excavator and sounds at the approach of danger (manufactured by Scanlaser, this device is also marketed under the colors of JCB). Digicat or the Leica, a portable column gives an estimate of the location and depth of a wire or a metal pipe. Still, it is not easy to identify, let alone to map networks entangled with these small sensors, which are mainly used to verify information already given. But regulation does not ask for more construction companies.