Locating concealed manholes and covers in Vienna, Lower Austria and Burgenland

Key facts at a glance

For you as a private customer

A manhole rarely disappears all at once. First a load of gravel is added, then the new driveway, then grass grows over it – and the next time round nobody knows where it was. It is looked for when there is a hurry: the drain has backed up, the meter is to be changed, the connection is to be jetted. The search is non-destructive and works from two sides: through the service from the inside, if there is an access at the house, otherwise from the surface. What follows is opening up in one place instead of three.

How the job runs

1. Enquiry and documents. You contact us on +43 (0) 2252 53169 or in writing to office@cft.at. Anything that exists helps: old plans, photographs taken before the alterations, the recollection of whoever last opened the cover.

2. Establishing access. What matters is whether there is a way into the service at the house – an inspection opening, a cleaning pipe, an open connection. If there is one, we work from the inside outwards. If there is not, we narrow down the area to be searched from the line of the service, the alignments and the falls.

3. Locating. With access we drive the service away from the house and take a bearing on the camera head at the surface via the sonde, until it stands beneath the manhole. Without access the magnetometer covers the area, and ground penetrating radar follows up where there is no iron.

4. Marking and handover. The point found is marked and photographed; exposing it is done by your plumber or your building contractor.

Equipment and methods

CCTV survey from the house connection outwards

The quickest way to the manhole rarely runs across the area, but through the service. If there is an inspection opening, a cleaning pipe or an open connection at the house, we push the camera in there and drive outwards – with the fall, in the direction in which the waste water runs. The manhole is where the service arrives: at the junction, at the change of direction, where two runs come together. The image also says what is waiting there before anybody opens up. An opening the camera can pass through is needed; bends, displaced joints, roots and the reach of the rods set the limit.

Sonde location in the camera head

The camera image on its own gives only the distance in metres, not the place in the garden. A transmitter sonde therefore sits in the camera head: it radiates from a single point, and its position can be taken at the surface together with a depth reading, down to 2.5 m. When the head stands in the junction, the operator stands above the manhole. This allows a plastic pipe on which no electromagnetic signal holds to be followed as far as the manhole as well.

Electromagnetic locating of the incoming pipe

If the service is metallic or has a tracer wire in it, it also works without a camera: an alternating current signal is applied to the pipe or the tracer wire and the route is followed at the surface. Where it ends, turns off or meets a second pipe run is usually where the manhole lies. This is the method with the greatest reach downwards: as far as 5 m. A connection point and a conductive path are needed; in densely occupied routes the signal couples across onto neighbouring services.

Magnetic locating with the magnetometer

If nothing at all is known – no access, no service, no clue – the direction is reversed and the area itself is searched. The magnetometer measures the disturbance of the earth’s magnetic field caused by a ferromagnetic body. Cast iron covers and frames therefore show up under asphalt, gravel and soil as well, without any applied signal, and they do so quickly and across the area. The search depth is one metre at most – deeper than that the disturbance is lost in the earth’s field. The second limit is set by the surroundings: plastic and concrete covers stay invisible, and where reinforcement, building rubble or metal fences lie, the deflection is lost in the interference.

Ground penetrating radar (GPR)

Where there is no iron, ground penetrating radar works the same area. An antenna sends short electromagnetic pulses into the ground; at every interface with different electrical properties, part of the pulse is reflected and recorded as a travel time. This makes concrete rings, the manhole structure and the void beneath it visible – precisely the cases in which the magnetometer finds nothing, and at two metres at most it reaches twice as deep. The limit is the ground: in cohesive or wet material the penetration depth falls, and under dense reinforcement the image becomes unreadable.

Costs and effort

We give neither a figure nor a guide price, because the search area, the make-up of the surfacing and the number of points being looked for determine the effort involved; we agree the cost range by telephone beforehand. For the re-survey the same applies as for any locating work: if our measurement was wrong, it is free of charge; if it was correct and the search simply was not precise enough or the digging not deep enough, the call-out is charged. Trace and access cover under buildings insurance does not apply here; it concerns leak detection after an escape of water.

Frequently asked questions