Modeling of coarse textured soils and their hydraulic properties
Constitutive relationships, namely the water retention characteristic curve and the relative hydraulic conductivity-capillary pressure function, are essential in the understanding and modeling of water and solute movement in subsurface vadose zone. In this thesis, it is proposed that coarse-textured soils, such as sands and loamy sands, can be conceptualized as porous media that consist of randomly sized (polydisperse) and randomly spatially distributed spheres. Using this conceptualization, two distinct groups of theoretical models for the soil hydraulic properties were developed: (i) empirical equations for fitting the water retention curve and the relative hydraulic conductivity function, and (ii) analytical expressions containing easily measured particle-size distribution parameters that can be used to estimate the retention curve. To further examine the proposed theories, a pore-morphology-based technique was introduced to simulate drainage of a porous medium. The technique was also extended to incorporate wetting simulation so that the role of interfacial area in the constitutive relationships could be investigated. It was found that all of the proposed models were comparable to existing retention models and also provided reasonable agreement with the observed data for coarse-textured soils. However, the model prediction failed to match the drainage simulation results, revealing that the proposed theories are inadequate, specifically due to the lack of consideration of pore connectivity. The voxel-based approach to estimate interfacial area was shown to produce estimates with good accuracy (as compared to the marching-cube algorithm). The functional dependence between the interfacial area, capillary pressure, and saturation was also confirmed by the simulations.
Govindaraju, Purdue University.
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