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Air entrapment and water infiltration in two-layered soil column
268A
PROPERTIES:PERMEABILITY t CAPILLARITY
956131 A multiple-pore-region concept to modeling mass transfer in subsurface media J. P. Gwo, P. M. Jardine, G. V. Wilson & G. T. Yeh, Journal of Hydrology, 164(1-4), 1995, pp 217-237. There is increasing evidence suggesting that pore structures, such as fractures and macropores, facilitate the transport of water and solutes along a preferential flow path while water and solutes are moved into micropores and rock matrices concurrently. This study presents a conceptual model, a multiple-pore-region (or multi-region) concept, to account for pore structures as well as the resultant widely distributed pore water velocities in macroporous media. A multi-region mechanism is proposed to account for the effect of localscale and field-scale heterogeneities on mass transport under variably saturated conditions. Two numerical codes for subsurface fluid flow and solute transport have been developed with the multi-region concept, in which a first order mass exchange model is adopted to simulate the redistribution of pressure heads and solute concentrations among pore regions. (from Authors) 956132 Relative air permeability as function of saturation in soil venting C. Stylianou & B. A. DeVantier, Journal of Environmental Engineering - AXE, 121(4), 1995, pp 337-347. The focus of this study was to characterize the relationship of the relative air permeability as a function of air saturation in soil-venting systems. A new laboratory apparatus was used to simulate the soil venting and measure the air permeability of soil samples. Sand samples wetted with mixtures of water and gasoline at different ratios were used. It was revealed that the prediction of relative air permeability for moist noncohesive soil can be made in terms of intrinsic permeability and airfilled porosity alone, and not the type of liquid present in the pores. (from Authors) 956133 Air-Permeability measurement for soil at low and high P-re S. A. Rodeck, B. A. DeVantier & B. M. Das, Journal of Environmental Engineering - AXE, 120(S), 1994, pp 13371343. Specimens of a clayey sand, compacted on the dry side of the optimum water content, have been tested for air permeability using a triaxial cell and mass flowmeter. The ratios between air permeabilities of specimens obtained from samples extracted 0” and 90” with respect to the direction of compaction revealed an order of magnitude difference in permeabilities. As a basis of comparison, high-permeability, dry-cohesionless sand samples were also tested in a modified version of the system under much lower driving pressures. Permeabilities were consistent with previously published results. (from Authors) 956134 Air entrapment and water infiltration in two-layered soil column H. Latiti, S. N. Prasad BE0. J. Helweg, Journal of Irrigation & Drainage Engineering - AXE, 120(5), 1994, pp 871-891. Presents the experimental results of one-dimensional unsaturated water infiltration under two conditions: vertical columns of homogeneous soil and vertical columns of twolayered soil. The purpose was to more accurately identify the movement of the wetting front under both conditions. The results showed that air pressure buildup was more pronounced in soil columns of two layers than in soil columns of one homogeneous layer. Water content in the top layer of a closed two-layer column was greater than the corresponding height in a homogeneous one-layer column. Flow conditions
and pressure buildup in the bottom layer retarded the wetting front at the interface until pressure reached a maximum value in the bottom layer. (from Authors) 956135 A method for simulating cadmium transport in soil: model development and experimental evaluation R. W. Al-Soufi, Journal of Hy&ology, 163(3-4), 1994, pp 233-247. A model for simulating cadmium transport in soil is presented. The calculation scheme is based on a threedimensional advection-dispersion model. Soil column experiments were conducted to validate the performance of the model. Also, batch tests were employed to determine the essential adsorption-desorption parameters that are required to operate the model. In light of the results, it was concluded that the model satisfactorily forecasts cadmium concentration and the pH of soil solution under varied acidic conditions. (from Author) 956136 Modelling unanticipated pore-water pressures in soft clays Jianhua Yin, J. Graham, J. I. Clark & Longjun Gao, Canadian Geotechnical Journal, 31(S), 1994, pp 773-778. Field observations in thin soft clay layers may show porewater pressures that increase for some time after the loading is applied. Reasons for these observations are not well understood. The paper shows how an elastic viscoplastic constitutive model incorporated into the consolidation equation can predict these pore-water pressure increases in soils that exhibit significant creep behaviour (or secondary compression). The phenomenon has been related to relaxation in regions of the profile from which drainage has not yet begun. (Authors) 956137 On uncertainty evaluation of contamhnt migration through clayey barriers Y. Honjo & T. Thavaraj, Canadian Geotechnical Journal, 31(5), 1994, pp 637-648. This paper presents a methodology to estimate parameters and to make predictions with quantified uncertainty for an advective-diffusive transport of nonreactive species and lowconcentration reactive species through saturated porous media. The methodology is put in the framework of inverse and forward analyses. The methodology facilitates the quantification of uncertainty in the estimated parameters as well as in the predictions. A case study consisting of sets of laboratory tests and field data taken from the literature is used to demonstrate the capability of the proposed methodologies. (from Authors) 956138 The influence of pore water velocity on transport of sorptive and non-sorptive chemicals through an unsaturated sand E. Shimojima L M. L. Sharma, Journal of Hydrology, 164(14), 1995, pp 239-261. A set of laboratory column experiments were conducted to study the transport of two relatively non-sorptive (Br, NOs) and three sorptive (P& simaxine, linuron) chemicals at three water flux conditions (q = 6.9, 3.1, 0.62 cm h-‘) through an unsaturated sand. Special attention was paid to the evaluation of the effects of pore-water velocity on transport of the chemicals as well as on their adsorption-desorption characteristics. The breakthrough curves for the adsorption process, observed at different depths under three different flux conditions could be scaled approximately using only two similarities, i.e. pore volume for ‘mobile’ water phase and Brenner number. A comparison between the modified BTCs of phosphate and simaxine for adsorption and desorption
PROPERTIES:PERMEABILITY t CAPILLARITY
956131 A multiple-pore-region concept to modeling mass transfer in subsurface media J. P. Gwo, P. M. Jardine, G. V. Wilson & G. T. Yeh, Journal of Hydrology, 164(1-4), 1995, pp 217-237. There is increasing evidence suggesting that pore structures, such as fractures and macropores, facilitate the transport of water and solutes along a preferential flow path while water and solutes are moved into micropores and rock matrices concurrently. This study presents a conceptual model, a multiple-pore-region (or multi-region) concept, to account for pore structures as well as the resultant widely distributed pore water velocities in macroporous media. A multi-region mechanism is proposed to account for the effect of localscale and field-scale heterogeneities on mass transport under variably saturated conditions. Two numerical codes for subsurface fluid flow and solute transport have been developed with the multi-region concept, in which a first order mass exchange model is adopted to simulate the redistribution of pressure heads and solute concentrations among pore regions. (from Authors) 956132 Relative air permeability as function of saturation in soil venting C. Stylianou & B. A. DeVantier, Journal of Environmental Engineering - AXE, 121(4), 1995, pp 337-347. The focus of this study was to characterize the relationship of the relative air permeability as a function of air saturation in soil-venting systems. A new laboratory apparatus was used to simulate the soil venting and measure the air permeability of soil samples. Sand samples wetted with mixtures of water and gasoline at different ratios were used. It was revealed that the prediction of relative air permeability for moist noncohesive soil can be made in terms of intrinsic permeability and airfilled porosity alone, and not the type of liquid present in the pores. (from Authors) 956133 Air-Permeability measurement for soil at low and high P-re S. A. Rodeck, B. A. DeVantier & B. M. Das, Journal of Environmental Engineering - AXE, 120(S), 1994, pp 13371343. Specimens of a clayey sand, compacted on the dry side of the optimum water content, have been tested for air permeability using a triaxial cell and mass flowmeter. The ratios between air permeabilities of specimens obtained from samples extracted 0” and 90” with respect to the direction of compaction revealed an order of magnitude difference in permeabilities. As a basis of comparison, high-permeability, dry-cohesionless sand samples were also tested in a modified version of the system under much lower driving pressures. Permeabilities were consistent with previously published results. (from Authors) 956134 Air entrapment and water infiltration in two-layered soil column H. Latiti, S. N. Prasad BE0. J. Helweg, Journal of Irrigation & Drainage Engineering - AXE, 120(5), 1994, pp 871-891. Presents the experimental results of one-dimensional unsaturated water infiltration under two conditions: vertical columns of homogeneous soil and vertical columns of twolayered soil. The purpose was to more accurately identify the movement of the wetting front under both conditions. The results showed that air pressure buildup was more pronounced in soil columns of two layers than in soil columns of one homogeneous layer. Water content in the top layer of a closed two-layer column was greater than the corresponding height in a homogeneous one-layer column. Flow conditions
and pressure buildup in the bottom layer retarded the wetting front at the interface until pressure reached a maximum value in the bottom layer. (from Authors) 956135 A method for simulating cadmium transport in soil: model development and experimental evaluation R. W. Al-Soufi, Journal of Hy&ology, 163(3-4), 1994, pp 233-247. A model for simulating cadmium transport in soil is presented. The calculation scheme is based on a threedimensional advection-dispersion model. Soil column experiments were conducted to validate the performance of the model. Also, batch tests were employed to determine the essential adsorption-desorption parameters that are required to operate the model. In light of the results, it was concluded that the model satisfactorily forecasts cadmium concentration and the pH of soil solution under varied acidic conditions. (from Author) 956136 Modelling unanticipated pore-water pressures in soft clays Jianhua Yin, J. Graham, J. I. Clark & Longjun Gao, Canadian Geotechnical Journal, 31(S), 1994, pp 773-778. Field observations in thin soft clay layers may show porewater pressures that increase for some time after the loading is applied. Reasons for these observations are not well understood. The paper shows how an elastic viscoplastic constitutive model incorporated into the consolidation equation can predict these pore-water pressure increases in soils that exhibit significant creep behaviour (or secondary compression). The phenomenon has been related to relaxation in regions of the profile from which drainage has not yet begun. (Authors) 956137 On uncertainty evaluation of contamhnt migration through clayey barriers Y. Honjo & T. Thavaraj, Canadian Geotechnical Journal, 31(5), 1994, pp 637-648. This paper presents a methodology to estimate parameters and to make predictions with quantified uncertainty for an advective-diffusive transport of nonreactive species and lowconcentration reactive species through saturated porous media. The methodology is put in the framework of inverse and forward analyses. The methodology facilitates the quantification of uncertainty in the estimated parameters as well as in the predictions. A case study consisting of sets of laboratory tests and field data taken from the literature is used to demonstrate the capability of the proposed methodologies. (from Authors) 956138 The influence of pore water velocity on transport of sorptive and non-sorptive chemicals through an unsaturated sand E. Shimojima L M. L. Sharma, Journal of Hydrology, 164(14), 1995, pp 239-261. A set of laboratory column experiments were conducted to study the transport of two relatively non-sorptive (Br, NOs) and three sorptive (P& simaxine, linuron) chemicals at three water flux conditions (q = 6.9, 3.1, 0.62 cm h-‘) through an unsaturated sand. Special attention was paid to the evaluation of the effects of pore-water velocity on transport of the chemicals as well as on their adsorption-desorption characteristics. The breakthrough curves for the adsorption process, observed at different depths under three different flux conditions could be scaled approximately using only two similarities, i.e. pore volume for ‘mobile’ water phase and Brenner number. A comparison between the modified BTCs of phosphate and simaxine for adsorption and desorption