Slope profile measurement of sewer inverts

• Differential settlement may cause problems to sewer systems.
• Tilt meters can be integrated in a sewer inspection camera.
• Tilt meters can be used to obtain the slope profile of a sewer invert.
• We analyzed the quality of this measurement technique.
• Slope profile measurements are a valuable addition to visual sewer inspection.

This paper presents the results of a study into the quality of the measurement of the slope profile of a sewer. Slope profile measurements can be used to assess the correct alignment of newly constructed sewers or the position of sewer pipes after differential settlement. For the measurement of the sewer invert profile a sewer inspection camera equipped with an electronic tilt meter can be used. The accuracy of the results of this measurement technique is not only determined by the specifications of the electronictilt meter but also by the execution of the measurement and properties of the measured object. To assess the influence of the latter two, the sewer invert profile one sewer was measured ten times. Analysis of the measurement results showed that the random errors are small and cancel out. Therefore differences in the slope of individual sewer pipes can be measured fairly accurately. The determination of the difference in level between either end of the sewer is inaccurate because of the systematic error.