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Bureau Seminar, May 4, 2012

Deformation and hydraulic conductivity of aggregated soft earth materials

Link to streaming video: available 05.04.2012 at 8:55am

Dr. Markus Berli
Associate Research Professor for Environmental Hydrogeophysics Division of Hydrologic Sciences, Desert Research Institute

Fluid flow in deformable porous media operates at multiple scales and is of interest in geophysics, hydrology, agronomy, petroleum-, civil- and environmental engineering. In the presented study X-ray micro-tomography (XMT) and Finite Element Analysis (FEA) were used to connect pore-scale deformation with changes in hydraulic conductivity of aggregated soft earth materials, as for example soils. Predictions of impacts of soil deformation on intrinsic permeability and saturated hydraulic conductivity were obtained from FEA solutions of flow fields within the inter-aggregate pore space. For unsaturated conditions, we used the evolution of aggregate contact areas to predict predominantly intra-aggregate water flow and unsaturated hydraulic conductivity. Measurements of soil rheological properties coupled with images of deforming aggregate beds monitored with XMT were used to validate mechanical/morphological modeling. Measured evolution of pore space between spherical modeling-clay aggregates was in reasonable agreement with model calculations using rheology and initial geometry as sole inputs. Individual pores within cross sections through a porous sample under compaction showed reductions in both mean and variance of pore intrinsic permeability with increasing compaction. Despite predominantly vertical sample deformation, sample intrinsic permeability remained nearly isotropic (with only a slight additional decrease in the vertical direction). An analytical approximation for pore intrinsic permeability by Aissen (1951) was very similar to numerical results for the entire range of sample deformation, thereby providing a useful tool for estimating sample intrinsic permeability from images of complex pore cross-sectional areas. For unsaturated soil with bimodal pore distribution (intra- and inter-aggregate pores) model calculations agreed with results on evolution of hydraulic conductivity due to deformation reported in literature.


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