• Tunnel and Underground Space
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• v.16 no.4 s.63
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• pp.281-287
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• 2006

Intake of groundwater by tunneling in a mountainous area mostly results from groundwater flow through fractured parts of total rock mass. For reasonable analysis of this phenomenon the representative joint groups 1, 2, and 3 have been selected by previous investigations, geological/geophysical field tests and boring works. Three dimensional fractures were generated by the FracMan and MAFIC which is a three dimensional finite element model has been used to analyse a groundwater flow through fractured media. Monte Carlo simulation was applied to reduce the uncertainty of this study. The numerical results showed that the average and deviation of amounts of groundwater intaked into tunnel per unit length were $5.40{\times}10^{-1}$ and $3.04{\times}10^{-1}m^3/min/km$. It is concluded that tunnel would be stable on impact of groundwater environment by tunneling because of the lower value than $2.00{\sim}3.00m^3/min/km$ as previous and present standard on the application of tunnel construction.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2006.04a
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• pp.312-315
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• 2006

배수공법으로 터널을 설계할 때 다양한 지질조건에 따라 터널내로 유입되는 지하수 용수량과 배수관의 배수능력을 비교 검토하였다. 기존 설계 기준에 의한 터널 배수관은 다양한 지질조건을 가지는 대수층의 수리전도도에 따라 안정성 여부가 달라지는 것을 알 수 있었다. 기존 배수관 (${\Phi}300m/m$)으로 터널을 설계할 경우 투수성이 좋은 석회암 구간 및 파쇄대 구간에서는 문제가 생길 가능성이 높고, 풍화 받지 않은 암반층의 경우에는 터널길이 20km까지 지하수 용수량을 수용 가능한 것으로 판단된다.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 1994.03a
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• pp.12-23
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• 1994

터널의 방수형식은 배수형(Wet System)과 방수형(Dry System)으로 대별된다. 배수형은 터널의 아치부와 측벽부에만 방수막을 설치하고 이의 배면과 바닥으로부터 유입되는 지하수를 배수공을 통하여 배수처리하는 방식이며 경제성과 시공성이 우수하여 대부분의 도로 터널 및 지하철 등에 적용되어 왔다. 방수형은 터널의 주변장 전체를 방수시공하여 터널내로 유입되는 지하수를 완전히 차단하는 방법으로서, 이러한 방수형 터널은 경제성과 시공성은 불리하나, 지하수위 저하에 따른 압밀침하나 생태계 파괴 방지, 터널의 장기적 환경보전 및 운영유지비 감소 등의 이유로 최근 상당수의 도심지 지하철 터널에 계획되어 시공중에 있다. (중략)

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.5
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• pp.489-506
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• 2024

Excavation of tunnels below the groundwater table changes the hydraulic boundary conditions, causing flow towards the excavation face. Inflow into a tunnel is generally influenced by pre-excavation grouting, shotcrete lining, drainage system implementation, and the hydraulic deterioration of the drainage system. From the perspective of continuum theory, the groundwater inflow behavior due to excavation is very similar to the tunnel excavation behavior known as the convergence-confinement method. The groundwater inflow behavior due to tunnel excavation can be explained by the hydraulic convergence, while the behavior of shotcrete lining in limiting inflow can be inferred as hydraulic confinement. This study investigates the hydraulic convergence and confinement behavior using theoretical and numerical methods due to tunnelling. It is confirmed that the hydraulic convergence-confinement is exactly the same as the mechanical convergence-confinement concept. It is identified that the behavior is governed by the tunnel geometry, grout thickness and permeability, as well as the thickness and permeability of the support materials, such as shotcrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.4
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• pp.145-152
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• 2004

Red sedimentation substance contains large portion of Fe. The earth retaining structure of a tunnel and ground water containing more portion of Fe than other area are the major factor of this substance In case of white sedimentation substance, the most frequently founded ingredient is CaO, which is occurred in case grouting injection materials for ground reinforcement is transmitted into a tunnel system by ground water. This substance is doesn't affect safety of a tunnel Black sedimentation substance is often found in tunnels near station. This substance is a mixture of either white or red sedimentation substance and detergent material in station transmitted to a tunnel drainage system.

• Journal of the Korean GEO-environmental Society
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• v.7 no.2
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• pp.67-76
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• 2006

For a hydro power plant project, the headrace tunnel having a finished diameter of 3.3 m was constructed in volcanic rocks with well-developed vertical joint and high groundwater table. The intake facility was located 20.3km upstream of the powerhouse and headrace tunnel of 20km in length and penstock of 440m in height connected the intake and the powerhouse. The typical caldera lake, Lake Toba set the geology at the site the caving of the ground caused tension cracks in the vertical direction to be developed and initial stresses at the ground to be released. High groundwater table(the maximum head of 20bar) in the area of well-connected vertical joints delayed the progress of tunnel excavation severely due to the excessive inflow of groundwater. The excavation of tunnel was made using open-shield type TBM and mucking cars on the rail. High volume of water inflowraised the water level inside tunnel to 70cm, 17% of tunnel diameter (3.9m) and hindered the mucking of spoil under water. To improve the productivity, several adjustments such as modification of TBM and mucking cars and increase in the number of submersible pumps were made forthe excavation of severe water inflow zone. Since the ground condition encountered during excavation turned out to be much worse, it was decided to adopt PC segment lining instead of RC lining. Besides, depending on the conditions of the water inflow, rock mass condition and internal water pressure, one of the invert PC segment lining with in-situ RC lining, RC lining and steel lining was applied to meet the site specific condition. With the adoption of PC segment lining, modification of TBM and other improvement, the excavation of the tunnel under severe groundwater condition was successfully completed.

• Journal of the Korean GEO-environmental Society
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• v.15 no.6
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• pp.5-15
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• 2014

This study is to quantitatively evaluate the impact on surrounding groundwater of waterway tunnel excavation and cofferdam construction in which A-dam and B-dam, so prediction of groundwater fluctuation and tunnel lining installation was studied. As a result, drawdown of groundwater level during tunnel excavation and cofferdam construction occurred about 3.58 m in the tunnel shaft. The initial condition of groundwater level recovered by up to 90 % was simulated after the completed the construction of the tunnel and lining installation. Groundwater inflow in the tunnel evaluated was analyzed to have exceeding water design criteria of the tunnel. The groundwater inflow is reduced to maximum $0.006m^3/min/km$ after lining installation done in the tunnel, so effect of lining installation was evaluated as 93 % or more. Drawdown of about 0.04~0.31 m occurs in the houses and temples analysis of groundwater system of the surrounding area from construction. Drawdown has occurred nearly by considering annual groundwater level fluctuation of National Groundwater Observation Network.

• The Journal of Engineering Geology
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• v.14 no.3 s.40
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• pp.287-300
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• 2004

By using a simple conceptual model, a sensitivity analysis is performed to examine the effects of changing model parameters on the model outputs, the groundwater discharge and the radius of influence, induced by tunnel construction. The results indicate that the model outputs are most sensitive to the tunnel depth and the hydraulic conductivity, and their sensitivities vary with time. It is also revealed that the sensitivity of the specific yield in- creases constantly with time, and therefore it is as important as the hydraulic conductivity for constructing a wet-system tunnel. A transient model is suggested to simulate the stepwise tunnel excavation and the watertight lining. The model is used for a tunnel construction site to predict groundwater mow into the tunnel and the transient response of the surrounding aquifer system. The predicted results are highly sensitive to the hydraulic conductivites assigned by model calibration. Thus, a postaudit should be made to reduce the uncertainty of the predictive model.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.79-89
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• 2024

Excessive inflow of groundwater during tunnel excavation not only affects the stability and constructability of the tunnel, but is also one of the main causes of ground settlement due to groundwater level drawdown. The most commonly applied measure against excessive groundwater inflow during tunnel excavation in soil or fractured zone is to reduce the ground permeability coefficient by injecting grout material. Generally, the grouting area is assumed to be same as the plastic zone that occurs during tunnel excavation, but injecting grout material in the area of plastic zone is appropriate only for reinforcement grouting. In order to determine the thickness of cutoff grouting, the amount of reduction in the water permeability coefficient due to the application of cutoff grouting must be considered. In this study, a method for estimating the range of cutoff grouting considering the reduction in permeability coefficient was mathematically derived and evaluated through computer numerical analysis.

• Proceedings of the KSEG Conference
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• 2000.04a
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• pp.95-102
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• 2000