On the relationship between matric potential and dielectric properties of organic free soils: a sensitivity study

Wagner, Norman; Scheuermann, Alexander

doi:10.1139/t09-055

Cited by 54 publications

(67 citation statements)

References 81 publications

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“…The experimental results indicate three active relaxation processes in the investigated frequency-temperaturepressure range: two weak high-frequency processes α and β (associated with different binding states of water in the porous material) and a strong low-frequency process γ associated with counter-ion relaxation, Maxwell-Wagner effects and ice. To characterize the dielectric relaxation behaviour, a generalized fractional dielectric relaxation model (Wagner et al, 2007(Wagner et al, , 2011 was applied assuming three active relaxation processes with relaxation time of the ith process modelled with an Eyring equation (Wagner and Scheuermann, 2009). The strong γ process exhibits an apparent activation energy of 51 kJ mol −1 and shows a clear deviation from simple Debye behaviour.…”

Section: Discussionmentioning

confidence: 99%

“…where free enthalpy of activation or Gibbs energy G i (T , p) [kJ mol −1 ] and entropy of activation of the ith (Wagner et al, 2007;Wagner and Scheuermann, 2009).…”

Section: Dielectric Soil Propertiesmentioning

confidence: 99%

“…Buchner et al, 1999). Furthermore, Gibbs energy of the interface fluid G # d (T ) is a function of the distance from the particle surface (for quantitative approaches see Wagner and Scheuermann, 2009). The greatest upper limit of Fig.…”

Section: Dielectric Soil Propertiesmentioning

confidence: 99%

“…Simplified schematic illustration of the structure of an unsaturated soil sample: indicated are the contributions of the single components to the dielectric material properties in terms of a complex effective relative permittivity ε * r,eff = ε r,eff − j ·ε r,eff with real ε r,eff and imaginary part ε r,eff (cf. Wagner and Scheuermann, 2009). 60.8 kJ mol −1 is equal to the free enthalpy of activation of ice (Bockris et al 1963) and therefore corresponds to relaxation times in the kHz range. However, a lowest limit for the first molecular water layer in soils was suggested by Or and Wraith (1999) with 18 kJ mol −1 at 293.15 K, which corresponds to relaxation times in the GHz range.…”

Section: Dielectric Soil Propertiesmentioning

confidence: 99%

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Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy

Lorek

Wagner

2013

The Cryosphere

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Abstract.Water substantially affects nearly all physical, chemical and biological processes on the Earth. Recent Mars observations as well as laboratory investigations suggest that water is a key factor of current physical and chemical processes on the Martian surface, e.g. rheological phenomena. Therefore it is of particular interest to get information about the liquid-like state of water on Martian analogue soils for temperatures below 0 • C. To this end, a parallel plate capacitor has been developed to obtain isothermal dielectric spectra of fine-grained soils in the frequency range from 10 Hz to 1.1 MHz at Martian-like temperatures down to −70 • C. Two Martian analogue soils have been investigated: a Ca-bentonite (specific surface of 237 m 2 g −1 , up to 9.4 % w/w gravimetric water content) and JSC Mars 1, a volcanic ash (specific surface of 146 m 2 g −1 , up to 7.4 % w/w). Three soil-specific relaxation processes are observed in the investigated frequency-temperature range: two weak highfrequency processes (bound or hydrated water as well as ice) and a strong low-frequency process due to counter-ion relaxation and the Maxwell-Wagner effect. To characterize the dielectric relaxation behaviour, a generalized fractional dielectric relaxation model was applied assuming three active relaxation processes with relaxation time of the ith process modelled with an Eyring equation. The real part of effective complex soil permittivity at 350 kHz was used to determine ice and liquid-like water content by means of the Birchak or CRIM equation. There are evidence that bentonite down to −70 • C has a liquid-like water content of 1.17 monolayers and JSC Mars 1 a liquid-like water content of 1.96 monolayers.

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Section: Discussionmentioning

confidence: 99%

“…where free enthalpy of activation or Gibbs energy G i (T , p) [kJ mol −1 ] and entropy of activation of the ith (Wagner et al, 2007;Wagner and Scheuermann, 2009).…”

Section: Dielectric Soil Propertiesmentioning

confidence: 99%

Section: Dielectric Soil Propertiesmentioning

confidence: 99%

Section: Dielectric Soil Propertiesmentioning

confidence: 99%

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Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy

Lorek

Wagner

2013

The Cryosphere

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“…However, soils generally respond dielectrically in a broad frequency range. These responses not only originate from pore water but also from the soil composition, structure, and mineralogy, as well as many other important soil characteristics [18,19]. With continuing research, the dielectric soil property at around 1 GHz is found to be not only a function of water content, but also of porosity and saturation [20,21,22].…”

Section: Introductionmentioning

confidence: 99%

Mechanical, hydraulic, and dielectric characterisation of fine-grained soils during densification

Schwing¹

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Soil characterisation is of primary interest for several disciplines, including geotechnical and geo-environmental engineering, soil science, and agriculture. An upcoming and promising method for soil characterisation relies on the high-frequency electromagnetic measurement technique which provides the potential to explore and investigate soils. However, successful application of this technique requires a profound understanding of the multi-physical processes arising from interactions between soil as a porous medium and the propagation of electromagnetic waves. This thesis focuses on a coupled experimental investigation of the mechanical, hydraulic, and dielectric characterisation of fine-grained soil during densification.In the framework of this thesis, the following steps have been completed and novel findings have been made:1. Probe designs have been developed, modified and improved to measure the dielectric soil properties in a frequency range from 1 MHz to 3 GHz during shrinkage and compaction. A low-cost in-house-manufactured probe was introduced, which was specifically designed for standardised geotechnical soil shrinkage test. During preliminary investigations, the calibration procedure and performance of these sensors were experimentally and numerically tested. The results showed agreement in the targeted frequency window.2. Compaction and shrinkage tests on fine-grained soils were conducted in combination with dielectric and soil suction measurements. The shrinkage curve and soil water characteristic curve (SWCC) was established and successfully parameterised with physical based models. The complex permittivity was determined in a frequency range from 1 MHz to 3 GHz. The dielectric properties measured during the shrinkage test showed a sudden drop of complex permittivity which could be located in the residual shrinkage zone.3. A theoretical electromagnetic mixture approach was used to model the measured frequency dependent dielectric properties of soils during shrinkage and compaction based on the parameterised shrinkage curve and SWCC. The theoretical results were compared to the dielectric measurements on different fine-grained soils. The comparison ii showed that the real part of permittivity could be well predicted whereas the imaginary part suffered inaccuracies.4. A sensitivity analysis was performed with the theoretical electromagnetic mixture approach in consideration of the shrinkage behaviour and SWCC in order to investigate the influence of soil suction and dry density on the frequency dependent permittivity.The sensitivity analysis showed that the real part of the permittivity near 1 GHz was insensitive to changes in the soil suction and dry density. In the MHz range, the real part of the permittivity was more sensitive to changes in soil suction than it was to dry density. The imaginary part of the permittivity was generally observed to be more sensitive to soil suction over the entire frequency range.

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Dielectric relaxation behavior of Callovo‐Oxfordian clay rock: A hydraulic‐mechanical‐electromagnetic coupling approach

Wagner

Boré²,

Robinet³

et al. 2013

JGR Solid Earth

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[1] Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo-Oxfordian (COx) clay formation. High-frequency electromagnetic (HF-EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF-EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). The frequency-dependent HF-EM properties were further modeled based on a novel hydraulic-mechanical-electromagnetic coupling approach developed for soils. The results show the potential of HF-EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations.

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On the relationship between matric potential and dielectric properties of organic free soils: a sensitivity study

Cited by 54 publications

References 81 publications

Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy

Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy

Mechanical, hydraulic, and dielectric characterisation of fine-grained soils during densification

Dielectric relaxation behavior of Callovo‐Oxfordian clay rock: A hydraulic‐mechanical‐electromagnetic coupling approach

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