Gas transport in partially-saturated sand packs

Understanding gas transport in porous media and its mechanism has broad applications in various research areas, such as carbon sequestration in deep saline aquifers and gas explorations in reservoir rocks. Gas transport is mainly controlled by pore space geometrical and morphological characteristics. In this study, we apply a physically-based model developed using concepts from percolation theory (PT) and the effective-medium approximation (EMA) to better understand diffusion and permeability of gas in packings of angular and rounded sand grains as well as glass beads. Two average sizes of grain i.e., 0.3 and 0.5 mm were used to pack sands in a column of 6 cm height and 4.9 cm diameter so that the total porosity of all packs was near 0.4. Water content, gas-filled porosity (also known as gas content), gas diffusion, and gas permeability were measured at different capillary pressures. The X-ray computed tomography method and the 3DMA-Rock software package were applied to determine the average pore coordination number z. Results showed that both saturation-dependent diffusion and permeability of gas showed almost linear behavior at higher gas-filled porosities, while deviated substantially from linear scaling at lower gas saturations. Comparing the theory with the diffusion and permeability experiments showed that the determined value of z ranged between 2.8 and 5.3, not greatly different from X-ray computed tomography results. The obtained results clearly indicate that the effect of the pore-throat size distribution on gas diffusion and permeability was minimal in these sand and glass bead packs

Temperature effects on geotechnical properties of kaolin clay: Simultaneous measurements of consolidation characteristics, shear stiffness, and permeability using a modified oedometer

The increased worldwide use of shallow geothermal energy systems including ground source heat pumps (GSHPs) have given concerns of possible temperature effects on soil geotechnical properties. In this study, the effects of temperature on mechanical characteristics such as consolidation settlement, shear stiffness, and permeability of kaolin clay were investigated. A modified oedometer apparatus which allows the simultaneous measurements of consolidation settlement, shear wave velocity, and hydraulic conductivity was developed and used. Consolidation tests on preconsolidated kaolin samples (two sample sizes: ϕ 6 cm x H 10 cm and ϕ 6 cm x H 2 cm) were performed under sequentially increasing consolidation pressures at three different temperatures (5 °C, 15 °C, and 40 °C). Larger apparent preconsolidation pressure, Pac, was seen at higher temperature (40 °C) for both sample sizes, but only for samples having relatively high initial void ratios between 1.53 and 1.62. Relatively higher shear modulus as a function of void ratio was observed for samples at higher temperature, suggesting that changes in fabric structure (likely caused by enhanced inter-particle forces between clay particles at higher temperature) resulted in the increased shear stiffness and, thus, higher Pac at 40 °C. Oppositely, temperature effects on theManuscript received February 5, 2013. This work was partly funded by a grant from the Research Management Bureau, Saitama University, the grant-in-Aid for Scientific Research of Japan Society for the Promotion of Science (JSPS) (No.22860012), and a JSPS bilateral research project. This work was also partially supported by a CREST project, a research grant from the Japan Science and Technology Agency (JST).E. E. Mon is with Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (phone/fax: (+81) 48-858-3116; e-mail: [email protected]).S. Hamamoto, is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: [email protected])K. Kawamoto is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: [email protected]).T. Komatsu is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: [email protected]).P. Mødrup is with Department of Biotechnology, Chemistry, and Environmental Engineering, Aalborg University, 9000 Aalborg, Denmark. (e-mail: [email protected]). permeability of kaolin clay were not significant within the studied temperature range between 5 °C and 40 °C

Geotechnical Properties of Kanto Alluvial Soils based on Geochemical Survey

Chemical properties of pore water in soils have a great influence on interparticle bonding among clayey particles and, as a result, not only on their soil structure but also on their geotechnical properties. In this study, we analyzed ionic compositions in pore water extracted from alluvial soils deposited under different sedimentary environments in Kanto lowland area, Japan, and investigated the effect of the chemical compositions of pore water on the geotechnical properties such as compressibility and sensitivity. The following results were obtained: The ion concentrations of pore water measured by different extraction methods showed that the concentration of Na+ by the dilution method was higher than that by the centrifugation method, while the concentrations of Ca2+, Cl- and SO42- by the dilution method are significantly smaller than those by centrifugation method. The centrifugation method was recommended for evaluating geochemistry of the soils since the rotation speeds in the centrifugation method did not significantly affect the pore-water compositions. The geotechnical properties were highly related to the ion concentrations of pore water. Higher compression index and sensitivity were observed for the alluvial soils with higher monovalent/divalent ion ratio. In addition, more strong dependency of monovalent/divalent ion ratio on geotechnical properties was obtained for the alluvial soils with plasticity index larger than 30

Measurements and Modeling of Thermal Conductivity of Recycled Aggregates from Concrete, Clay Brick, and Their Mixtures with Autoclaved Aerated Concrete Grains

Cool road pavements contribute to mitigating urban heat islands. To evaluate the heat balance in paved surfaces and to select appropriate road construction materials that help suppress heat islands, an accurate understanding of heat transport parameters such as thermal conductivity (λ) and heat capacity (HC) is important. Recycled aggregates from construction and demolition waste, including scrap construction materials and industrial by-products, are often used for road construction; however, λ and HC of recycled aggregates especially for roadbeds are not fully understood. This study involved a series of laboratory tests to measure λ and HC of recycled concrete and clay brick aggregates (λ and HC increased with increasing volumetric water content (θ). Closed-form models for estimating λ(θ) were proposed using normalized thermal conductivity (λe) and effective saturation (Se). The new λe(Se) models performed well for the measured data compared to previously proposed models and would be useful to evaluate λ of recycled aggregates for roadbed materials

Gas Diffusivity and Thermal Properties of Compost-mixed Soils under Variable Water Saturation

Gas and heat transport through compostmixed landfill cover soils affect the emission of toxic gases and methane oxidization processes. In this study, we mixed soils with three different composts in the ratio of either 1:5 or 1:10 (compost:soil) to understand the effect of compost mixing for gas diffusivity and thermal properties. The gas diffusion coefficient (Dp), thermal conductivity ( ), and heat capacity (HC) were measured for soils, composts, and compost-mixed soils at different soil-water matric potentials ( ) starting from nearly saturated to = -10,000 cm H2O and dry conditions. Data were fitted to the Brooks-Corey soil-water retention curve model to estimate the bubbling pressure ( b). For all materials, Dp increased linearly with increased air content ( ), and the Penman-Call linear Dp( ) model with the model slope (C) and threshold soil-air content ( th) fitted the data well. The th values increased with increasing compost content, relating non-linearly to the Brooks-Corey b but highly linearly to the soil macroporosity. Analogous to the Dp( ) model, Penman-Call type linear ( ), and HC( ) models with slopes (C′ and C′′) and intercepts ( 0 and HC0, thermal conductivity and heat capacity at a volumetric water content of = 0) captured reasonably well the data measured from dry to wet conditions. The C′ for varied depending on the compost ratio and decreased with increasing compost ratio. The C′′ for HC, on the other hand, had less effect on the compost mix. The thermal properties under the dry condition, 0 and HC0, were well correlated to the volumetric solid content. The results from this study will be helpful towards designing compost-mixed landfill cover soils with optimal heat and gas transport characteristics

PAHs concentration and toxicity in organic solvent extracts of atmospheric particulate matters and sea sediments

The concentration of polycyclic aromatic hydrocarbons (PAHs) and the toxicity to marine bacteria (Vibrio fischeri) were measured for the organic solvent extracts of sea sediments collected from an urban watershed area (Hiroshima Bay) of Japan and compared with the concentrations and toxicity of atmospheric particulate matters. Among atmospheric particulate matters, the PAHs concentration was highest in FPM collected during cold seasons. The concentrations of sea sediments were 0.01-0.001 times those of atmospheric particulate matters. 1/EC50 was 1-10 L g-1 PM for atmospheric particulate matters and 0.1-1 L g-1 dry solids for sea sediments. These results imply that toxic substances from atmospheric PM are diluted several tens or hundreds times in sea sediments. The ratio of the 1/EC50 to PAHs concentration ((1/EC50)/16PAHs) was stable for all sea sediments (0.1-1 L μg-1 16PAHs) and was the same in the order of the magnitude as that of FPM and CPM. The ratio of sediments collected from the west was more similar to that of CPM while that of the east was to FPM, possibly because of hydraulic differences among water bodies. The PAHs concentration pattern analyses (principal component analysis and isomer ratio analysis) were conducted and from the results. PAHs pattern of sea sediments was fairly different from that of FPM and CPM. Comparison to previously conducted PAHs analyses suggested that biomass burning residues comprised a major portion of these other sources.This work was supported by Kurita Water and Environmental Foundation and Grant-in-Aid for Scientific Research (C