• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.2 s.9
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• pp.119-125
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• 2003

Water flow in unsaturated soils is affected by two mathematical equations called soil water-characteristic curve and permeability-suction relationship. Soil water-characteristic curve is an equation showing volumetric water content-suction relationship. Many researchers have presented equations for the relationships. This paper illustrates the importance of correctly determining the two relationships when analyzing unsaturated water flows. Results from two methods, Gardner (1958) and Fredlund et al. (1994), are used for comparison purposes. Numerical simulations of water flow by finite element method are performed using the two methods. The results by the numerical simulations are compared with the field data which was obtained from time-domain reflectometry (TDR) probes in Delaware County, Ohio. This data was obtained by the Seasonal Instrumentation Program which is included as a part of the Strategic Highway Research Program (SHRP).

• Environmental Engineering Research
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• v.11 no.5
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• pp.241-249
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• 2006

A mathematical model is described for the prediction of convective upward transport of an organic solvent driven by evaporation at the surface, which is known as the major transport mechanism in the in-situ photolysis of a soil contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD). A finite-element model was proposed to incorporate the effects of multiphase flow on the distribution of each fluid, gravity as a driving force, and the use of hysteretic models for more accurate description of k-S-p relations. Extensive numerical calculations were performed to study fluid flow through three types of soils under different water table conditions. Predictions of relative permeability-saturation-pressure (k-S-p) relations and fluids distribution for an illustrative soil indicate that hysteresis effects may be quite substantial. This result emphasizes the need to use hysteretic models in performing flow simulations including reversals of flow paths. Results of additional calculations accounting for hysteresis on the one-dimensional unsaturated soil columns show that gravity affects significantly on the flow of each fluid during gravity drainage, solvent injection, and evaporation, especially for highly permeable soils. The rate and duration of solvent injection also have a profound influence on the fluid saturation profile and the amount of evaporated solvent. Key factors influencing water drainage and solvent evaporation in soils also include hydraulic conductivity and water table configuration.

• Journal of Soil and Groundwater Environment
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• v.18 no.6
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• pp.48-55
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• 2013

This study aimed at characterizing unsaturated zone at the source zone area contaminated by DNAPL and investigating feasibility of soil vapor extraction (SVE). Five boreholes with three multi-level screens at the depth of 3.0~4.5 m, 5.5~7.0 m, and 8.0~12.0 m were installed at the source zone. Pneumatic tests were performed to determine the permeability of porous medium. Permeability was estimated to be 81.6 to 203.7 darcy, depending on the applied solutions, which was contradicted by grain size analysis of cored soil samples leading to 3.51 darcy. This is due to air flow through gravel pack during the early stage of pneumatic test. Pressure-drawdown curve in the late stage also well showed the leaky aquifer type, indicating air leakage to the ground. Air flow tests were also carried out to investigate air flow connectivity between multi-level wells, indicating that the horizontal air flow was well developed between the lower screens of the wells, not between the upper and middle screens due to the leakage to the surface. For the SVE test, there was no noticeable variation in TCE vapor concentration between three different test runs: 1. 8 hours daily for 5 days, 2. 24 hours together with air blowing at another well (BH1), 3. five consecutive days. Even for five-day consecutive test, total amount of removed TCE was estimated only to be as low as 46.5 g.

• Journal of the Korean Geotechnical Society
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• v.21 no.3
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• pp.119-131
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• 2005

Seepage analysis through unsaturated zone based on the theory of unsaturated flow is commonly performed to evaluate dam safety. However, the concepts of unsaturated soil behavior have not been transferred into the hands of practicing geotechnical engineers since the problems involving unsaturated soils often have the appearances of being extremely complex. The behavior of dam such as seepage rate and the pore water pressure distribution is different according to the unsaturated hydraulic properties, but nevertheless simply assumed properties have been used due to insufficient data from domestic soils. In this paper, the effect of unsaturated hydraulic properties on the behavior of dam was studied through a series of numerical analyses, and then the results were discussed. It is observed that water table moves at a (aster rate, as the values of unsaturated soil parameter a and n increase. The value of m showed opposite trend. The sensitivity calculated using the approximation form showed maximum values near the water table. And the value of n that is related to the slope of soil water characteristic curve gives greatest influence on the change of sensitivity with time.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.73-83
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• 2006

Seepage analysis through unsaturated zone based on the theory of unsaturated flow is commonly performed to evaluate dam safety. However, the concepts of unsaturated soil behavior have not been transferred into the hands of practicing geotechnical engineers since the problems involving unsaturated soils often have the appearances of being extremely complex. There is variability and uncertainty associated with the unsaturated hydraulic properties that in turn will lead to variability in predicting unsaturated soil behavior such as seepage rate and the pore water pressure distribution. In this paper, measurements of the soil-water characteristic curve and saturated hydraulic conductivity for the core material of dam were conducted. Then, finite element stochastic analysis was used to capture the effect of unsaturated hydraulic properties on the seepage behavior of dam. It is observed that the amount of seepage increases, as the values of unsaturated soil parameters a and n increase. The values of m and p showed opposite trend.

• Proceedings of the Korea Water Resources Association Conference
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• 1993.07a
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• pp.183-190
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• 1993

• Proceedings of the Korea Water Resources Association Conference
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• 1997.05a
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• pp.465-470
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• 1997

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.15-25
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• 2003

To evaluate the effect of trapped air bubbles in horizontal drains on discharge capacity, unsaturated discharge capacity tests are carried out for four types of drains selected according to the size of section as well as the shape of core. Unsaturated discharge capacities with the elapse of time, the increase of confining pressures, and hydraulic gradients are examined and are compared with saturated discharge capacities. It is found that the unsaturated discharge capacities at a hydraulic gradient of 0.01 decreased by 17%~80% due to the remained air bubbles in the drains compared with the saturated discharge capacities. It is caused by the fact that the horizontal direction of water flow is not consistent with the direction of movement of floating air bubbles in case of horizontal drains. Especially, far the drain with filament shaped core, discharge capacities decreased significantly due to the difficulty in removing air bubbles.

• Geotechnical Engineering
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• v.14 no.5
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• pp.191-204
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• 1998

The feasibility of fly ash was evaluated as an alternative liner material to the conventional clay liner of landfills through modeling and laboratory experiments. In order to consider the effect of unsaturation on water flow through the liner, analyses were made to compare flow characteristics in saturated liner with that of unsaturated one. Contaminant migration characteristics in liners were investigated by batch experiment and modeling, in which phenol was employed as a model was solved by numerical techniques of finite difference method and predictor-corrector method to deal with high non-linearity. Sequential method was used to handle the system of differential equations. Results show that the alternative liner material is more capable of cutting off water flow in unsaturated condition and in preventing phenol from passing through it. It can be seen that, under the flow conditions considered in this study, the conventional saturation approach underestimates the amount of water passing through the liner and doers the cut-off capability against phenol significantly.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.235-254
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• 1991

In the analysis of seepage behavior through the porous media, unsaturated domain should be included for obtaining more accurate results. The seepage programs considering its domain have been developed and practically used widely. The programs are reviewed and two case studies are presented in this paper. The case studies are performed using PC-SEEP and obtained good results for the cases of saturated-unsaturated transient flow.