Application of impedance spectroscopy and tomography to monitor calcite deposits in drainage pipes

Abstract

The determination of calcite deposits in drainage pipes plays an important role in tunnel construction as well as in ongoing operation. If these deposits are not detected in time, expensive maintenance work is required compared to a simple flush. If detected early, rinsing with a pressurized water jet is usually sufficient. For this reason, research is carried out on various sensor systems that allow the growth of the calcite layer to be monitored. Impedance tomography (EIT) and impedance spectroscopy (EIS) can be used as measuring methods since both allow the estimation of the layering of air, water, and calcite for the given two-dimensional pipe geometry. The solution to the estimation problem is also made easier by the fact that the materials involved, PVC, calcite, water, and air, have very different electrical conductivities and permittivities and are also known to form horizontal layers. Thus, simple electronics and signal processing schemes are possible.This article presents a cost-effective drainage pipe monitoring solution that uses distributed impedance measurements to determine the layering and roughly estimates the thickness of layers of air, water, and calcite within these pipes. Several thousand pipe segments are required for tunnel lengths of several kilometers, which is why a very inexpensive and simple implementation of these sensors is required.