• Tunnel and Underground Space
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• 제18권5호
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• pp.366-374
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• 2008

Tunnelling under water table induces many geotechnical problems because of groundwater. In subsea tunneling, reduction of face stability can induce flooding in the vicinity of a fracture zone characterized by high permeability and high water pressure. In this study, the effects of high water pressure on the stability of a tunnel face in a limited zone with high permeability(hazardous zone) are analyzed. On the basis of the 'advance core' concept, the seepage force acting on a hypothetical cylinder ahead of a tunnel face is modeled. This study focuses on the hydraulic behavior of the ground ahead of the tunnel face by three-dimensional steady-state seepage analyses. The impact of the hazardous zone on the seepage force and stability of the tunnel face are simulated and analyzed. In light of the analysis results, it is estimated that the distance from the tunnel face to the exterior boundary limit, which the seepage force significantly affects the stability of the tunnel face, of a hypothetical cylinder is approximately 5 times the tunnel radii. Despite the restrictive assumptions of this study, the results are highly indicative regarding the risks of hazardous zones.

• Journal of the Korean Geotechnical Society
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• 제27권5호
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• pp.17-31
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• 2011

This paper presents the results of a numerical investigation on the behavior of earth retaining wall system with emphasis on the groundwater lowering. Using the 2D stress-pore pressure coupled analysis, the effects of ground excavation and groundwater interaction were examined using wall horizontal deformation, ground surface movement, plastic strain pattern, effective stress distribution and axial stress of strut. In addition, based on the results from a parametric study on a wide range of soil profile and initial ground water table level, the ranges of wall displacement and ground deformation were suggested quantitatively.

• Tunnel and Underground Space
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• 제23권6호
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• pp.506-520
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• 2013

While geothermal energy provides the only base-load power among renewable energy sources, its development has been carried out predominantly in volcanic area. EGS (Enhanced Geothermal System) is a ubiquitous technology that can allow the geothermal power generation virtually in any area. This manuscript introduces the current state-of-the-art of EGS development in the world and presents the hydraulic stimulation technology and associated microseismicity which are key technical component in EGS. Finally this paper suggests the key research areas required in Korea for further development of EGS.

• Journal of the Korean Geotechnical Society
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• 제20권3호
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• pp.33-46
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• 2004

This paper presents the effect of groundwater on tunnel excavation. Fundamental issues in tunneling under high groundwater table are discussed and the effect of groundwater on tunnel excavation was examined using a 3D stress-pore pressure coupled finite-element analysis. Based on the results the interaction mechanism between the tunnelling and groundwater is identified for cases having different lining permeabilities. Examined items include pore pressures around lining and lining stresses. Face deformation behavior as well as ground surface movement patterns was also examined. Besides, the effect of grouting pattern was investigated. The results indicated that the effect of groundwater on tunnel excavation increases lining stresses as well as ground movements, and that the tunnel excavation and groundwater interaction can only be captured through a fully coupled analysis. Implementations of the findings from this study are discussed in great detail.

• Journal of the Korean GEO-environmental Society
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• 제6권2호
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• pp.15-20
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• 2005

Moutain side ditch is constructed at the top of cutting slopes around road and it drains the surface water that flowed from upper part. About 70% of a country is composed of mountains so occurrence of cutting face by road general observation is necessary. Instability of cutting face is increased by permeation of underground water by rainfall the summer, pore water pressure increases. However, moutain side ditch is constructed on the top of cutting slopes has some troubles. For example, difficulty of qualify control and lack of drainage faculty. Therefore, stability variation of cutting slope is analyzed by hydraulic conductivity and construction depth of mountain side ditch and effective depth of mountain side ditch is decided in this paper.

• Tunnel and Underground Space
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• 제24권6호
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• pp.418-429
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• 2014

Induced seismicity related to four energy development technologies that involve fluid injection or withdrawal: geothermal energy, conventional oil and gas development including enhanced oil recovery (EOR), shale gas recovery, and carbon capture and storage (CCS) is reviewed by literature investigation. The largest induced seismic events reported in the technical literature are associated with projects that did not balance the large volume of fluids injected into, or extracted from the underground reservoir. A statistical observation shows that the net volume of fluid injected and/or extracted may serve as a proxy for changes in subsurface stress conditions and pore pressure, and other factors. Energy technology projects that are designed to maintain a balance between the amount of fluid being injected and the amount of fluid being withdrawn, such as geothermal and most oil and gas development, may produce fewer induced seismic events than technologies that do not maintain fluid balance, such as long-term wastewater disposal wells and CCS projects.

• Journal of the Korean Geotechnical Society
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• 제31권5호
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• pp.67-74
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• 2015

Unlike the primary consolidation settlement, the settlement of ground water lowering is not considered separately because of relatively small residual settlement. But the allowed residual settlement (30 mm) of the concrete track in the high-speed railway may be exceeded due to unexpected excessive ground water lowering. This study analyzed the effect of the settlement according to the ground water level change using finite element analysis of stress-pore pressure coupling model, and compared the analysis results with the measured data. As a result, the range of elasticity modulus satisfying the allowable settlement was proposed, and it is suggested that settlement due to ground water level changes should be reflected in the design.

• Journal of Korea Water Resources Association
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• 제34권5호
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• pp.449-458
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• 2001

In order to verify the numerical model, which was developed to simulate the behavior of the two-phase fluid flow in a single fracture, the characteristic equation of relative permeability was incorporated into the developed numerical model, and the computed results were compared with the experimental results of the model test. As results of the sensitivity analysis on the roughness and the aperture size of fracture, the gas velocity was inversely proportional to the fracture roughness, and not proportional to the square of aperture size which is usually observed in single phase flow in a single fracture. The numerical model was applied to the underground LPG storage terminal in order to check the field applicability. The simultaneous flow of water and gas in accordance with the operation pressures in a single fracture near cavern was simulated by the model. It was shown that the leaked gas was able to be controlled in a single fracture neither by the pressure of operation nor by that of groundwater in case the fracture became smoother in roughness and smaller in aperture size.

• Journal of the Korean Geotechnical Society
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• 제30권5호
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• pp.55-65
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• 2014

Most shield tunnels are designed based on the assumption of a undrained condition. But they are operated as drained tunnels in which underground water flows and passes through a drainage facility. Therefore, it is necessary that the drainage condition be considered in the shield tunnel design. In this research, new testing device which can simulate the underground tunnel located below ground water level, was developed. Total stress and pore water pressure were examined and an inflow water into an inner pipe was measured using the testing device. Test results showed that the total stress, which was the sum of effective stress and pore pressure, increased more in an undrained condition and an inflow water into an inner pipe was proportional to the water pressure but inversely proportional to the loading stress. Consequently, if the drainage is considered in the shield tunnel design, the more economical design can be expected because of the stress reduction of the lining.

• Tunnel and Underground Space
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• 제18권1호
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• pp.10-19
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• 2008

Most of flooding cases in tunnels are associated with huge inrushes of water due to the fracture zone with very high water head. To find out the causes and countermeasures for flooding cases, a dozen of tunneling cases are studied. Case studies presented here show that if the flooding had been forecasted and pre-drained prior to the tunnel excavation, such accidents could have been prevented. From this observation, we suggest a new horizontal drainage system with pre-investigation and pre-drainage concept. Seepage analyses are performed to analyze the water head reduction effect on the tunnel face by drainage pipes during the construction of subsea tunnels. Drainage system analyses are performed to analyze performance of the drainage system. These analysis results show that the suggested horizontal pre-drainage system provides a clear drainage and water head reducing effect. Finally, the proposed system can be a new alternative to the present water controlling methods applied to subsea tunnels.