In contrast to laterals, the location of main sewers can theoretically be determined on the basis of the manholes. These are visible above ground and are usually located in the public domain. It is generally assumed that the sewers run in a straight line between the manholes. However, there are always cases where the run of the sewer deviates from this principle to such an extent that the deviation is of importance for the planning of rehabilitation measures. "In such situations, an exact pipe run measurement is advisable, even in main sewers," says project manager Lüdeke Grasshoff (GEODOC GmbH), confirming the decision of Kiel's sewage department. They decided not only to thoroughly clean and inspect the pressure pipeline, but also to have the exact pipe run recorded at the same time with northing and easting values as well as elevation data (x,y,z coordinates). René Mittelstädt, site manager at Kiel's sewage department, attached particular importance to the elevation data. For this purpose, the executing company Canal-Control + Clean Umweltschutzservice GmbH (CCC) uses hydrostatic height measurement and 3D-GeoSense pipe run measurement. With this innovative technology developed by IBAK Helmut Hunger GmbH & Co. KG, the pipe run is automatically recorded with a 3D sensor integrated into the inspection camera in a single operation together with the inspection. 3D GeoSense measurement is supported by hydrostatic height measurement which enables the elevation to be measured accurately to a centimetre via a water column in the cleaning hose.

The first task was to clean the pressure sewer. "Cleaning of the 612 m long reach without further access with a difference in elevation of 17 m against the direction of flow, i.e. upstream, made corresponding demands on our employees and of course also on the equipment," Lüdeke Grasshoff notes. Here, up to 35 t of sewer sand were brought to the surface daily by several vehicles and almost the entire pipe section was reached. A daily inspection with a high-resolution pan and rotate camera on the IBAK truck to check the cleaning results provided precise information on the cleaning progress and the effectiveness of the methods used. These TV control inspections were already carried out with 3D GeoSense technology, so that the camera position could be seen at any time from the dynamically generated network graphics on the screen. This gave the cleaner accurate information about the changes in the slope of the reach and the position of the cascades. Cleaning could thus be matched precisely and effectively to the pipe geometry.

Following the cleaning, the pressure sewer was completely cut open in order to insert the 5 m long inspection elements. In just two days, the CCC team, in close cooperation with René Mittelstädt, mastered the inspection and electronic measurement of the reach using IBAK's 3D technology. The x,y,z coordinates were determined while the camera was moving both forwards and backwards. Each journey immediately provided a realistic site plan with northing and easting values and the elevation data of the pressure sewer on the monitor in the operator's section. The T 76 camera tractor has an electronic stability function that automatically returns it to the bottom of the pipe in the event of deviations of position. The camera with the integrated sensor was always aligned parallel to the pipe axis to ensure precise measurement. In order to achieve very high accuracy, the same measurement section, which in this case was very long, was repeatedly traversed and an average value was formed from the measurements. This function is supported by the new IKAS evolution software component for 3D-GeoSense pipe run measurement of sewer reaches.

Hydrostatic height measurement was included selectively in the recording of the pipe run. This is a measurement method that reliably determines the elevation of sewer systems with very high accuracy. With the aid of a pressure sensor, this method measures the water column in the cleaning hose. First, a zero measurement was made on the manhole cover to obtain a reference pressure for all subsequent measurements. Then the cleaning nozzle was flushed in immediately after the camera tractor via which the metre count is made. The position of the cleaning nozzle could be precisely monitored with the IBAK RETRUS rear view camera mounted on the camera tractor. The cleaning nozzle was stopped at any desired points to measure the water column again. From this, the IBAK software IKAS evolution calculated the change in pressure as compared to the zero measurement and determined the elevation of the reach at the measuring point with centimetre accuracy.