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@PHDTHESIS{Breede:838904,
      author       = {Breede, Katrin},
      title        = {{C}haracterization of effective hydraulic properties of
                      unsaturated porous media using spectral induced polarization
                      ({SIP})},
      volume       = {175},
      school       = {Universität Bonn},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2017-07410},
      isbn         = {978-3-89336-875-4},
      series       = {Schriften des Forschungszentrums Jülich / Reihe Energie
                      $\&$ Umwelt},
      pages        = {XIV, 72 S : Ill., graph. Darst},
      year         = {2013},
      note         = {Dissertation, Universität Bonn, 2012},
      abstract     = {Groundwater is a life-sustaining but vulnerable resource
                      which is endangered by contaminants. Soil acts as an
                      important protective buffer for groundwater and, therefore,
                      the understanding of flow and transport processes in soils
                      is of utmost importance. However, the prediction
                      capabilities of flow and transport models in the vadose zone
                      are often limited due to an insufficient knowledge about the
                      structural and textural heterogeneity of the soil. To obtain
                      more information about soil structure, texture and
                      heterogeneity, as well as hydraulic parameters, non-invasive
                      electrical methods may be employed in laboratory and
                      field-scale studies. One of the more promising electrical
                      methods is spectral induced polarization (SIP), which
                      measures the complex electrical conductivity in the
                      low-frequency range from 1 mHz to 45 kHz. Recently, this
                      method has been used to predict the saturated hydraulic
                      conductivity of consolidated and unconsolidated porous
                      media. To better understand the mechanisms causing
                      polarization and to extend the range of SIP applications to
                      the vadose zone, it is important to investigate how the SIP
                      response is affected by water content. In addition, it might
                      be possible to relate the SIP response to the unsaturated
                      hydraulic conductivity. Therefore, the general aim of this
                      thesis is the determination of effective hydraulic
                      properties of unsaturated and unconsolidated porous media
                      from SIP measurements. In a first step, a laboratory
                      measurement setup was developed that allows combined
                      electrical and hydraulic measurements on unconsolidated
                      porous media. The experimental design allows draining
                      samples in various consecutive pressure steps and water
                      outflow is automatically recorded to determine the water
                      content. Measurements of the complex electrical conductivity
                      are conducted using a high-accuracy electrical impedance
                      spectrometer. Experiments were conducted on unconsolidated
                      quartz sand and three sand-clay mixtures with 5, 10, and 20
                      weight-percent clay. The measured complex electrical
                      conductivity was interpreted using a Debye decomposition
                      approach that provides the DC resistivity, the total
                      chargeability, and a distribution of relaxation times. The
                      influence of water content on electrical properties like
                      real and imaginary part of the complex electrical
                      conductivity, phase shift, and the parameters obtained from
                      Debye decomposition was investigated for all four
                      artificially mixed sediment samples. The measured
                      resistivity magnitude and phase spectra and their dependence
                      on water content are clearly different for each mixture. For
                      pure sand, the phase values increased with decreasing water
                      content over the entire frequency range and a phase peak
                      appeared for moderate to low water content. The phase
                      spectra of the sand-clay mixtures show the same behavior as
                      the pure sand. In addition, a shift of the phase peak to
                      higher frequencies with decreasing water saturation was
                      observed for all samples. This shift suggests that
                      relaxation time and length become smaller with decreasing
                      water content, which is related to the smaller pores that
                      are still saturated at lower water content.The relationship
                      between unsaturated hydraulic properties and SIP parameters
                      was also investigated. The results show a clear power-law
                      relationship between the matric potential and the peak
                      relaxation time of the sand-clay mixtures. However, two
                      different slopes were observed for this relationship, one
                      for matric potentials greater than -120 cm and another one
                      for smaller ones. The observed slope was quadratic for
                      matric potentials > -120 cm and linear for matric potentials
                      below -120 cm. The quadratic relationship was attributed to
                      diffusion processes, but the linear relationship indicates a
                      hitherto unknown relaxation process. Using the empirical
                      relationship between the relaxation time and the matric
                      potential, respectively pore radius, and a simplified
                      version of the Mualem-van Genuchten model, a relationship
                      between the relaxation time and the unsaturated hydraulic
                      conductivity was obtained. The slope of this power-law
                      dependence between unsaturated hydraulic conductivity and
                      relaxation time depends on the width of the pore size
                      distribution as expressed by the semiempirical n parameter
                      of the Mualem-van Genuchten model. It was concluded that the
                      unsaturated hydraulic conductivity can be determined from
                      spectral induced polarization using the relaxation time and
                      additional information like the n parameter of the
                      Mualem-van Genuchten model.},
      cin          = {IBG-3},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/838904},
}