Thermography includes the measurement of surface temperatures of an object.

A well-known application of these thermal images is detecting errors or defects in the thermal insulation of buildings. These masurements are best made in winter and at night do avoid the interference of direct sunlight. The thermographic images will show up weak points in the thermal insulation by way of "temperature anomalies".

Tunnel thermography

There has always been a keen interest in using thermographic methods also for examining tunnels, the idea being to detect cavities or water in the lining material and to show these as temperature anomalies.

Since 1982, SPACETEC has been one of the first companies to deal with this subject systematically, eventually developing a method with a high level of reliability and objectivity.

As the measurements must be made quickly and within a short space of time because of the surface temperatures in the tunnel changing permanently, the scanner systems must be able to cope with certain velocities and speeds.

It is only then that a uniform and interpretable temperature image can be obtained of the entire structure.

A simultaneous visual image helps in the interpretation. "Harmless" temperature anomalies are sorted out.

Measurements with the SPACETEC TS2 tunnel scanner meet these conditions in a perfect manner.

Thermography observing certain conditions

If thermography is to "screen" the tunnel lining like in an X-ray image, certain precisely defined conditions must be fulfilled. These include direct measurments and the observation of temperatures inside the structure over a certain period of time.

The required conditions are not consistent. This is why the date for the measurement - depending on weather - can only be fixed at short notice.

As soon as the conditions favouring the successful thermographic measurement exist, SPACETEC uses its own autonomous measuring unit to control via the telecommunication network.

The measuring results obtained under these controlled conditions are then analysed and interpreted by SPACETEC after recording.

SPACETEC describes the results in plain language without judging the general condition of the structure. Typical findings of such thermographic recordings include:

- Wet spots
- Water/moisture in the lining
- Cavities, air inclusions
- Non-homogeneous material composition

There is no need for the user to deal with the interpretation of thermal images. The most important results are presented and described in a report.

Thermography without observing certain measuring conditions

Under certain circumstances, the tunnel lining cannot be "screened" with thermography because the required conditions do not exist or exist only after an unforeseeable period of time.

Major causes include climatic conditions, but also the nature and location of the structure which allows no adequate through ventilation.

Administrative reasons may be another cause for not gaining access to a tunnel structure at short notice.

In cases such as these, a purely visual inspection may be sufficient which at least shows all superficial phenomena.

Many recordings which SPACETEC have made without observing any conditions show, however, that the thermographic images show clear and identifiable signals.

As the precise thermal flow tends to be unknown, the appropriate temperature patterns are not always easy to interpret. These temperature patterns nevertheless deliver additional and analysable information besides the purely visual image.

As far as water is concerned, even minute quantities generate a clear signal as a result of the evaporation cooling effect. At best, a visual image would simply show a dark spot which could also be caused by dust or similar deposits.

Depending on season, the temperature differences between day and night can be substantial. To evaluate the condition of the spraycrete (locating spalling spots), this may be sufficient from time to time.

SPACETEC has meanwhile gathered experience with over 100 km of thermographic recordings.

In summarising, the benefit of these recordings is that they draw attention to certain effects - effects which are not necessarily discovered by observing the visual image.

Thanks to the technology of the SPACETEC 3 three-channel scanner, we are able to offer this additional information for a reasonable extra charge.

Things that cannot be measured

Right from the beginning, SPACETEC has approached the subject of tunnel thermography on a respectable basis. Before SPACETEC accept a contract, we first point out what can be done and what cannot. We do not believe in "trial and error" at the customer's expense if we know straightaway that things do not make sense, for instance

- Locating leaks in seals

Measuring layer thickness, e.g. the thickness of the lining


Potential water-conducting spots at depths >30 cm

Why not contact our experts if you have any specific questions?

Locating insulation defects in buildings

Tunnel thermography: cavities showing blue,
water in the lining: red - magenta

A visual image avoids incorrect conclusions in the interpretation.

Monitoring the measuring conditions in a tunnel

Water (from leakage damage) in the lining of a new tunnel structure

Spalling at a block joint, highlighted by the thermal image

Defect (hole) in a setting joint

Cap seal with functioning drainages

Imminent spalling of spraycrete sections

Reliability: As much as seven years later, we can still reproduce our results. Changes provide information on the progress of damage.

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