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  • BB

  • Low‐Field Borehole NMR Applications in the Near‐Surface Environment

    • Authors: Kirkland, C.M.;  Advisor: -;  Participants: Codd, S.L. (2018)

  • The inherent heterogeneity of the near subsurface (<200 m below the ground surface) presents challenges for agricultural water management, hydrogeologic characterization, and engineering, among other fields. Borehole nuclear magnetic resonance (NMR) has the potential not only to describe this heterogeneity in space nondestructively but also to monitor physical and chemical changes in the subsurface with time. Nuclear magnetic resonance is sensitive to parameters of interest like porosity and permeability, saturation, fluid viscosity, and formation mineralogy. Borehole NMR tools have been used to measure soil moisture in model soils, and recent advances in low‐field borehole NMR instru...
  • BB

  • Magnetic Resonance Monitoring and Numerical Modeling of Soil Moisture during Evaporation

    • Authors: Merz, S.;  Advisor: -;  Participants: Balcom, B.J.; Enjilela, R.; Vanderborght, J.; Rothfuss, Y.; Vereecken, H.; Pohlmeier, A. (2018)

  • Evaporation from bare soil surfaces can be restrained to a great extent with the development of a dry layer at the soil surface where capillary hydraulic conductance ceases and water flow proceeds only by gas phase transport. Model calculations and preliminary experiments with model porous media have shown that this surface layer can be very thin. An accurate characterization of these processes is required, which is provided by noninvasive magnetic resonance (MR) methods. The evaporative drying of a silt loam and a sandy loam was monitored at high spatial resolution in laboratory experiments. The MR data were used to assess the performance of two numerical models: (i) the Richards equ...
  • BB

  • Quantification of Water Content during Freeze–Thaw Cycles: A Nuclear Magnetic Resonance Based Method

    • Authors: Tian, H.;  Advisor: -;  Participants: Wei, C.; Lai, Y.; Chen, P. (2018)

  • In analyzing the phase transition and water migration processes in multiphase porous systems, it is helpful to properly evaluate the unfrozen capillary water content and adsorptive water content, respectively. In this study, an innovative procedure was developed to determine the total, adsorptive, and capillary water contents in frozen soils based on the nuclear magnetic resonance (NMR) technique. We found a threshold value of the proton spin–spin relaxation time, T2, that separates the unfrozen pore water into two distinct regimes: the adsorptive regime for small T2 values and the capillary regime for large T2 values. We showed that the relationship between adsorptive (or capillary) ...