Indirect measurements of water content using TDR-inferred dielectric permittivity and electrical resistivity

Bruna De Carvalho Faria Lima Lopes,Laís De Carvalho Faria Lima Lopes,Alessandro Tarantino,A Tarantino,E Ibraim

doi:10.1051/e3sconf/20199202005

Bruna De Carvalho Faria Lima Lopes, Laís De Carvalho Faria Lima Lopes + Show 3 more

Open Access

https://doi.org/10.1051/e3sconf/20199202005

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Abstract

The measurement of moisture distribution in Engineered Barrier Systems (EBS) in salt mines and deep geological disposals is essential in order to monitor fluid ingress and record data for long-term security analyses. Additionally, soil moisture content has influence over the mechanical properties of the soil as well as plant growth, soil stability and contaminant transport to cite some. Therefore, finding affordable and reliable ways to determine moisture content, quickly and in the field without sampling, is of great interested among people in different subject areas. Time-domain reflectometry (TDR) has become a recognized electromagnetic method for non-destructive measurement of dielectric permittivity and electrical conductivity of moist porous materials. It turns out that both these measurements depend on the material moisture content, among other things. This paper presents a series of calibration tests performed on soil samples. TDR probes were used to obtain the dielectric permittivity and electrical conductivity of the samples. As a consequence, relationships between these measurements and the samples' volumetric water content were later established. These relationships can then be used to indirectly determine that important information of water content on similar soil material using cheap, quick and non-destructive TDR probes.

Highlights

Soil moisture is a part of the three phase system of the soil, which includes soil minerals, moisture and air [1]
Soil moisture content is used as an important parameter for water balance studies, slope stability analysis and performance evaluation of various geotechnical structures such as pavements, foundations, earth dams, retaining walls, hazardous waste disposal repositories and contaminant transport within the vadose zone [4]
The velocity of the pulse travelling in the soil which is determined by Time-domain reflectometry (TDR) is a measure of the permittivity of the soil

Summary

Introduction

Soil moisture is a part of the three phase system of the soil, which includes soil minerals (solids), moisture and air [1]. Physical, chemical, mineralogical, mechanical, geotechnical, hydrological and biological properties of the soils are significantly dependent on soil moisture content [3]. There are various methods for assessing soil moisture content, including the gravimetric method, which is one of the most widespread and easiest, and methods that use soil physical properties related to moisture to indirectly estimate the soil water content, including temperature, electrical resistance, capacitance, spectrometry and timedomain reflectometry (TDR) [3], amongst others. TDR probes were used to obtain the apparent permittivity and electrical conductivity of four different soil samples. Relationships between these measurements and the samples’ volumetric water content were later established

Background

Materials and methods

Results and discussions

Final remarks