Permeability (earth sciences)

About: Permeability (earth sciences) is a research topic. Over the lifetime, 15424 publications have been published within this topic receiving 288535 citations.

Geotechnical Properties of Paper Mill Sludges for Use in Landfill Covers

Abstract: This study investigates the geotechnical properties of seven paper mill sludges. Paper mill sludges have a high water content and a high degree of compressibility and behave like a highly organic soil. Consolidation tests reveal a large reduction in void ratio and high strain values that are expected due to the high compressibility. Triaxial shear-strength tests conducted on remolded and undisturbed samples showed variations in the strength parameters resulting from the differences in sludge composition (i.e., water content and organic content). Laboratory permeability tests conducted on in-situ specimens either met the regulatory requirement for the permeability of a landfill cover or were very close. With time, consolidation and dewatering of the paper sludge improved the permeability of cover. Freezing and thawing cycles increased the sludge permeability about one to two orders of magnitude. Maximum permeability changes occurred within 10 freeze and thaw cycles.

Modeling metamorphic fluid flow with reaction-compaction permeability feedbacks

Abstract: Existing models of metasomatic flow do not allow for the effect that reaction has on the flow patterns. Instead, it is assumed that the volatiles produced are negligible in volume compared to those infiltrated and that reaction does not modify permeability. This is clearly unlikely to be true for infiltration-driven decarbonation reactions. The rates of porosity creation by reaction and porosity loss by creep have been calculated for a representative volume of calcite –quartz-wollastonite marble, and it is found that, even for a weak calcite matrix, the rate of porosity generation by reaction is likely to outstrip the collapse of porosity, as long as the system is out of equilibrium. We have applied a self-consistent 1D finite-difference model to the reaction of calcite + quartz to wollastonite in a 10m thick marble, in response to influx of H2O rich fluid, with fixed boundary conditions. The model allows us to evaluate the effect of reaction on the porosity structure and fluid pressure variation across the layer, from which local Darcy fluxes can be evaluated. The progress of reaction that we model is constrained by hydrological considerations, with the requisite parameters recalculated as reaction progresses, assuming creep compaction of rock under the stress difference between lithostatic and fluid pressures. We fnd that the volume of fluid realised by decarbonation, driven by influx of H20, is sufficient to create a back-flow, so that further advancement of the reaction front is only possible as a result of diffusion of water against the Darcy flux. The effect of creep driven by differences between fluid pressure and lithostatic pressure is to reduce the permeability of the layer and especially reduce the secondary porosity developed in the zone at and behind the advancing reaction front. We predict that in a 3D situation, the porous zone of reacted marble becomes a conduit for layer-parallel flow, and the secondary porosity is infilled by calc-silicate minerals due to silica metasomatism.

Permeability anisotropy of consolidated clays

Abstract: Abstract Consolidation of clays tends to result in changes in particle orientation and pore size distribution as well as progressive reduction of porosity and permeability with increasing effective stress. Clay particles are expected to rotate normal to an axial load, thus decreasing flow path tortuosity parallel to the particle alignment direction and increasing tortuosity normal to the particle alignment. This results in the development of anisotropic permeability, such that the horizontal permeability of a consolidated sediment is greater than the vertical permeability at any given porosity. Within any uniform layer, levels of permeability anisotropy are modest. Typically, permeability anisotropy produced by consolidation of natural clays is in the range 1.1–3 and does not reach the high levels predicted by simple models of clay particle reorientation. The discrepancy arises from particle clustering and irregularities in particle packing. Although somewhat higher levels of anisotropy may exist as a consequence of lamination within individual beds, values > 10 that are known to exist on the formation scale are produced by strong contrasts between the permeabilities of interlayered beds. As argillaceous sediments have permeability ranges of many orders of magnitude, apparently subtle lithological layering in a shale unit may lead to a highly anisotropic flow behaviour.

Soil Water Retention and Relative Permeability for Conditions from Oven-Dry to Full Saturation

Abstract: Common conceptual models for unsaturated flow assume that the matric potential is attributed to the capillary force only. These models are successful at high and medium water contents but often give poor results at low water contents. The lower bound of existing water retention functions and conductivity models was extended from residual water content to the oven-dry condition (i.e., zero water content) by defining a state-dependent residual water content for a soil drier than a critical value. The advantages of the extended water retention functions include not refitting the retention parameters from the unextended model, its reduction to the unextended form when the soil is wetter than the critical value, and its compatibility with existing relative permeability models. In addition, a hydraulic conductivity model for film flow in a medium of smooth uniform spheres was modified by introducing a correction factor to describe the film flow-induced hydraulic conductivity for natural porous media. The total unsaturated hydraulic conductivity is the sum of those due to capillary and film flow; it smoothly transits between capillary-dominated flow and film-dominated flow over the full range of water content. The film flow is insignificant when the soil is wetter than the critical water content, and, vice versa, the capillary flow is insignificant when the soil is drier than the critical water content. The extended retention and conductivity models were tested with measurements. Results show that, when the soil is at high and intermediate water content, there is no difference between the unextended and the extended models as defined by the theory. When the soil is at low water content, the unextended models overestimate the water content but underestimate the conductivity. The extended models match the retention and conductivity measurements well.