• Journal of Korea Water Resources Association
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• v.30 no.1
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• pp.63-73
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• 1997

Finite element model is established for the simulation of groundwater flow due to water curtain around underground oil storage Choleski decomposition method. The symmetric global conductance matrix is solved by vector storage Choleski decomposition method. The model is verified through comparison with the results of electric analogy. For the application of this model to real site, the finite element meshes are constructed according to representative vertical cross and longitudinal sections. In cross-sectional analysis, potential and flow distributions are compared based on the cavern pressure and horizontal water curtain. For longitudinal section, effects between nearly located caverns with or without vertical water curtain are analyzed. These results prove that the established model can be used as a tool for flow analysis around underground caverns.

• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.43-55
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• 2018

AGF (Artificial Ground Freezing) method is a temporary ground improvement method which can apply to all types of soil with the purpose of high stiffness and low hydraulic conductivity. However, the groundwater flow and the heterogeneity of the ground increase the uncertainty of the ice-column formation which hinders the reliability of this method. The effects of groundwater flow and layered heterogeneity on ice-wall integrity by AGF method were analyzed using finite element analysis program for a coupled thermo-hydro phenomena in the freezing ground. Groundwater flow changes circular ice-column into elliptical shapes and increases the time required for the formation of ice walls. The previous theoretical formula overestimated the completion time of the ice wall and the critical groundwater velocity by neglecting the thermal interaction between adjacent ice-columns. Numerical results presented the corrected formula and verified the proposed equation for the dimensionless ice-wall completion time. In the layered heterogeneous ground, the thickness of the layer with higher hydraulic conductivity and its relative magnitude were found to be important factors in the ice-wall completion time and critical velocity.

• KIEAE Journal
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• v.17 no.3
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• pp.119-124
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• 2017

Purpose: Groundwater heat pump (GWHP) system has high coefficient of performance than conventional air-source heat pump system and closed-loop type geothermal system. However, there is problem in long-term operation that groundwater raise at the diffusion well and reduced at the supply well. Therefore, it is necessary to accurately predict the groundwater flow, groundwater movement and control the groundwater level in the wells. In this research, in consideration of hydrogeological characteristic, groundwater level and groundwater movement were conducted analysis in order to develop the optimal design method of the two-well system using the pairing pipe. Method: For the optimum design of the two-well system, this research focused on the design method of the pairing pipe in the simulation model. Especially, in order to control the groundwater level in wells, pairing pipe between the supply well and diffusion well was developed and the groundwater level during the system operation was analyzed by the numerical simulation. Result: As the result of simulation, the groundwater level increased to -2.65m even in the condition of low hydraulic conductivity and high pumping flow rate. Consequently, it was found that the developed system can be operated stably.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.156-166
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• 2001

A stochastic continuum(SC) modeling technique was developed to simulate the groundwater flow pathway in fractured rocks. This model was developed to overcome the disadvantageous points of discrete fracture network(DFN) modes which has the limitation of fracture numbers. Besides, SC model is able to perform probabilistic analysis and to simulate the conductive groundwater pathway as discrete fracture network model. The SC model was formulated based on the discrete fracture network(DFN) model. The spatial distribution of permeability in the stochastic continuum model was defined by the probability distribution and variogram functions defined from the permeabilities of subdivided smaller blocks of the DFN model. The analysis of groundwater travel time was performed to show the consistency between DFN and SC models by the numerical experiment. It was found that the stochastic continuum modes was an appropriate way to provide the probability density distribution of groundwater velocity which is required for the probabilistic safety assessment of a radioactive waste disposal facility.

• Journal of Soil and Groundwater Environment
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• v.14 no.1
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• pp.1-10
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• 2009

Groundwater flow due to intake of horizontal collector well in riverbank filtration site was analyzed by use of numerical groundwater modeling program (FEFLOW 5.1). Drawdowns of groundwater table nearby collector well were evaluated according to variations of several conditions; pumping rate, thickness of aquifer, offset distance from well to shore line of stream, conductance of streambed. It is observed that the drawdowns of groundwater table are clearly changed according to the variations of these conditions. The results of sensitive analysis shows that the thickness of alluvial aquifer and the offset distance are more sensitive than the conductance of streambed in evaluation of drawdown. This result implies that hydrogeological conditions, as like thickness of aquifer and its distribution in the site are important factors in site selection and evaluating the availability of riverbank filtration intake using horizontal collector well system. It is also revealed that numerical modeling using FEFLOW with 1-D discrete element feature can give efficient quantitative evaluation of horizontal collector well and estimation of availability of riverbank filtration site.

• Tunnel and Underground Space
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• v.14 no.3
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• pp.229-240
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• 2004

Coastal aquifers may serve as major sources fur freshwater. In many coastal aquifers, intrusion of seawater has become one of the major constraints imposed on groundwater utilization. The management of groundwater in coastal acquifers means making decision as to the pumping rate and the spatial distribution of wells. Several numerical techniques for flow and solute transport simulation can provide the means to achieve this goal. As a basic study to predict the intrusion of seawater in coastal phreatic aquifers, the coupled flow and solute transport analysis was conducted by use of the 3-D finite element code, SWICHA. In order to understand how the location and the shape of freshwater-seawater transition zone were affected by the boundary conditions and hydrogeologic variables, parametric study was carried out.

• Journal of Soil and Groundwater Environment
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• v.15 no.6
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• pp.53-63
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• 2010

Pneumatic fracturing is an emerging tool to enhance the remediation efficiency of contaminated unsaturated zones by injecting high pressure air and inducing artificial fracture networks. Pneumatic fracturing is reported to be well suited for the cases where the contaminated unsaturated zone thickness is less than 5 m as many contaminated domestic sites in Korea. Nevertheless, there have been almost no studies carried out on the site-specific efficiency and the optimized design of pneumatic fracturing considering the unsaturated zone characteristics of Korea. In this study, we employ numerical simulations to compare the efficiency of pneumatic fracturing on the aspect of the site remediation and the porosity improvement at several hypothetic unsaturated zones composed of four typical soil types. According to the simulation results, it is found that the zone with fine grains soil such as clay and silt shows better efficiency than the zone composed of coarse grains in terms of air flow and porosity enhancements. The results imply that pneumatic fracturing may improve the efficiency of site reclamation by jointly or independently applied to the many contaminated sites in Korea.

• Tunnel and Underground Space
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• v.17 no.2 s.67
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• pp.109-118
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• 2007

The excavation damaged zone (EDZ) is an area around an excavation where in situ rock mass properties, stress condition. displacement. groundwater flow conditions have been altered due to the excavation. Various studies have been carried out on EDZ, but most studies have been focused on the mechanical bahavior of EDZ by in situ experiment. Even though the EDZ could potentially form a high permeable pathway of groundwater flow, only a few studies were performed on the analysis of groundwater flow in EDZ. In this study, the' hydraulic EDZ' was defined as the rock Lone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation. And hydraulic EDZ (hydraulic aperture changed zone) estimated by two-dimensional DEM program was considered in three-dimensional DFN model. From this approach the groundwater flow characteristics corresponding to hydraulic aperture change were examined. Together. a parametric study was performed to examine the boundary conditions that frequently used in DFN analysis such as constant head or constant flux condition. According to the numerical analysis, hydraulic aperture change induced by the hydraulic-mechanical interaction becomes one of the most important factors Influencing the hydraulic behavior of jointed rock masses. And also from this study, we suggest the proper boundary condition in three-dimensional DFN model.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.705-712
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• 2000

The fluid generally flows through fractures in crystalline rocks where most of underground storage facilities are constructed because of their low hydraulic conductivities. The fractured rock is better to be conceptualized with a discrete fracture concept, rather continuum approach. In the aspect of fluid flow in underground, the simultaneous flow of groundwater and gas should be considered in the cases of generation and leakage of gas in nuclear waste disposal facilities, air sparging process and soil vapor extraction for eliminating contaminants in soil or rock pore, and pneumatic fracturing for the improvement of permeability of rock mass. For the purpose of appropriate analysis of groundwater-gas flow, this study presents an unsteady-state multi-phase FEM fracture network simulator. Numerical simulation has been also conducted to investigate the hydraulic head distribution and air tightness around Ulsan LPG storage cavern. The recorded hydraulic head at the observation well Y was -5 to -10 m. From the results obtained by the developed model, it shows that the discrete fracture model yielded hydraulic head of -10 m, whereas great discrepancy with the field data was observed in the case of equivalent continuum modeling. The air tightness of individual fractures around cavern was examined according to two different operating pressures and as a result, only several numbers of fractures neighboring the cavern did not satisfy the criteria of air tightness at 882 kPa of cavern pressure. In the meantime, when operating pressure is 710.5 kPa, the most areas did not satisfy air tightness criteria. Finally, in the case of gas leaking from cavern to the surrounding rocks, the resulted hydraulic head and flowing pattern was changed and, therefore, gas was leaked out from the cavern ceiling and groundwater was flowed into the cavern through the walls.

• Water for future
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• v.22 no.1
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• pp.81-90
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• 1989

A numerical simulation technique of three-dimensional finite difference model is developed to study the groundwater flow system in Dejima, an upland area which faces Kasumigaura Lake. For general perspectives of the groundwater flow system, a steady state three-dimensinal model is simulated. For the sedimentary mud formations which are found in the representative formation, three situations where the horizontal permeability is equal to 10 times and 100 times of the vertical one. The finite difference grid used in the simulation has 60$\times$50$\times$30=90,000 nodes. A converged solution with a tolerance of 0.001 meter of hydraulic head is set. Having determined the flow net by using a steady state three-dimensional model, the results for the three cases of hydraulic conductivity are compared with the results of the tracer methods (Bae and Kayane, 1987). With the aid of four representative vertical cross-sections, groundwater flow systems in the study area are assumed. The results of these are reasonally good comparable with the results of the basin yield and thd recharge-discharge distribution 8.