Effect of boundary conditions on measured water retention behavior within soils

Galindo-Torres, S., Scheuermann, A., Pedroso, D. M. and Li, L. (2013). Effect of boundary conditions on measured water retention behavior within soils. In: American Geophysical Union (AGU) Fall Meeting 2013, San Francisco, CA, USA, (). 9-13 December, 2013.

Author Galindo-Torres, S.
Scheuermann, A.
Pedroso, D. M.
Li, L.
Title of paper Effect of boundary conditions on measured water retention behavior within soils
Conference name American Geophysical Union (AGU) Fall Meeting 2013
Conference location San Francisco, CA, USA
Conference dates 9-13 December, 2013
Publication Year 2013
Sub-type Published abstract
Open Access Status
Language eng
Formatted Abstract/Summary
The Soil Water Characteristic Curve (SWCC) is a practical representation of the behavior of soil water by relating the suction (difference between the air and water pressures to the moisture content (water saturation). The SWCC is characterized by a hysteresis loop, which is thought to be unique in that any drainage-imbibition cycle lies within a main hysteresis loop limited by two different curves for drainage and imbibition. This 'uniqueness' is the main argument for considering the SWCC as a material-intrinsic feature that characterizes the pore structure and its interaction with fluids. Models have been developed with the SWCC as input data to describe the evolution of the water saturation and the suction within soils. One example of these models is the widely used Richard's equation. In this work we present a series of numerical simulations to evaluate the 'unique' nature of the SWCC. The simulations involves the use of the Lattice Boltzmann Method (LBM) within a regular soil, modelling the flow behavior of two immiscible fluids: wetting and non-wetting. The soil is packed within a cubic domain to resemble the experimental setups that are commonly used for measuring the SWCC. The boundary conditions ensure that the non-wetting phase enters through one cubic face and the wetting phase enters trough the opposite phase, with no flow boundary conditions in the remaining 4 cubic faces. The SWCC known features are inspected including the presence of the common limit curves for different cycles involving varying limits for the suction. For this stage of simulations, the SWCC is indeed unique. Later, different boundary conditions are applied with the two fluids each injected from 3 opposing faces into the porous medium. The effect of this boundary condition change is a net flow direction, which is different from that in the previous case. A striking result is observed when both SWCC are compared and found to be noticeable different. Further analysis is conducted to examine how the fluids are distributed inside the porous medium. This distribution is quantified by the measurement of the interfacial area which behaves also differently between the two configurations. Hassanizadeh proposed an unique relation among saturation, suction and interfacial area, which has been validated experimentally. However we found that such relation is not 'unique' and instead depends on the flow and boundary conditions. While future experimental tests on these results need to be carried out, the simulated SWCC behaviors raise serious questions about the current experimental set-up for measuring the soil water retention characteristics.
Q-Index Code EX
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Conference Paper
Collection: School of Civil Engineering Publications
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Created: Mon, 31 Mar 2014, 13:35:12 EST by Dr Alexander Scheuermann on behalf of School of Civil Engineering