Author(s): Shiyao Wang; Andy Nichols; Jonathan Davidson

Linked Author(s): Shiyao Wang

Keywords: Electrical conductance sensor; Hydraulic permeability; Electrical impedance spectroscopy; Sediment monitoring and management; Grain size

Abstract: Sedimentation in urban drainage systems can lead to a reduction in flow capacity and potentially to surcharge and overflow, but our ability to monitor sedimentation is limited. Several previous studies have addressed the measurement of sediment from different perspectives and using various principles. However, these existing measurement systems usually include several component devices, which means high cost and energy consumption and complicated manual operation during measurement. In this study, a new sediment sensor based on electrical impedance spectroscopy (EIS) has been explored as a method for characterising sediments in sewers. The hydraulic permeability, which is one of the core properties of sediment, was investigated in this study, and the relationship between hydraulic permeability (σ) and electrical conductance (G) of saturated sediments has been explored under laboratory conditions. The investigated sediment samples include six sizes of glass spheres (5 mm, 3 mm, 2 mm, 0.6-1.5 mm, 0.5 mm and 0.1-0.43 mm) and five different types of sand mixture (from 5 mm to 1 mm). The sediment sensor was fabricated on a flexible PCB with four electrodes, providing a versatile form factor for installation inside pipe systems. The frequency dependent electrical conductance was measured between each possible pair of electrodes using EIS and equivalent circuit simulations with a frequency range from 1 Hz to 9 MHz. Hydraulic permeability of samples was measured using a constant head permeability test based on Darcy’s Law. The results demonstrate a power law form (G=aσ^b-c) relationship between the measured electrical conductance and the hydraulic permeability, which is consistent with the well-known Archie’s Law and Kozeny-Carman equation. The dependence of parameters a,b, and c on the granular media type was examined. The porosity and grain size distribution were found to have significant influence on the measured impedance spectrum. Moreover, the relationship between the electrode spacing and measured electrical conductance was characterised from the experiments. These data enable an empirical model to estimate the depth and physical characteristics of porous media based on the measured impedance spectrum. This sediment sensor is simple to manufacture, easy to use, and feasible to be developed for characterisation of other porous media.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221034

Year: 2022