• Title/Summary/Keyword: fracture aperture

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박테리아에 의한 클로깅 현상에 따른 임계 상태 균열 암반의 유체투과율 감소에 관한 전산 연구

  • 한충용;강주명;최종근
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • 2001.04a
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    • pp.73-76
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    • 2001
  • We have simulated the effect of fracture characteristics on reduction of effective permeability of the fractured rocks due to in-situ bacteria growth. A nutrient is injected continuously for growth of in-situ bacteria. We used a power law for fracture length distribution and a fBm for fracture aperture spatial distribution. The results show that in-situ bacteria growth reduces the Permeability hyperbolically, but the porosity of backbone fracture does not change significantly. It shows that reduction of the permeability proceeds at faster speed for smaller value of length exponent(a) and for larger value of Hurst exponent(H). The fracture length distribution has stronger effect on speed of reduction than the aperture spatial distribution. The time needed to reduce permeability is inversely proportional to the hydraulic gradient.

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Characterization of the Spatial Distribution of Fracture System at the Rock Block Scale in the Granitic Area (화강암지역의 암반블록규모 단열체계 분포특성 연구)

  • 김경수;배대석;김천수
    • Tunnel and Underground Space
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    • v.12 no.3
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    • pp.198-209
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    • 2002
  • To assess deep geological environment for the research and development of hish-level radioactive waste disposal, six boreholes of 3" in diameter were installed in two granitic areas. An areal extent of the rock block scale in the study sites was estimated by the lineament analysis from satellite images and shaded relief maps. The characterization of fracture system developed in rock block scale was carried out based on the acoustic televiewer logging in deep boreholes. In the Yuseong site, the granite rock mass was divided into the upper and lower zones at around -160m based on the probabilistic distribution characteristics of the geometric parameters such as orientation, fracture frequency, spacing and aperture size. Since the groundwater flow is dependent on the fracture system in a fractured rock mass, the correlation of the fracture frequency and cumulative aperture size to the hydraulic conductivity was also discussed.

A Study of the Influence of Void Geometry on Fracture Closure and Permeability (간극의 기하학적 특성이 절리의 수직변형 및 투수성에 미치는 영향에 관한 연구)

    • Tunnel and Underground Space
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    • v.12 no.4
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    • pp.304-311
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    • 2002
  • This study reports the influence of vocid geometry on fracture closure and permeability from numerical experiments. As the aperture distributions of rock fractures are characterized by statistical methods, synthetic fractures have successfully been simulated in this way. Based on the generated fracture models, models for fracture closure and flow calculation have been developed. A fracture closure model has been developed by considering the asperity compression and half-space deformation, and flow calculations have been performed using a finite difference method adopting a local cubic law. The results of numerical experiments have shown that the increase in the aperture spatial correlation leads the fracture closure and the decrease in fracture permeability to increase. Also, it has been indicated that there is an implicit relation between fracture normal stiffness and permeability. The importance of this study is to enhance the understanding the hydro-mechanical behavior of fractured rock massed due to engineering projects.

Televiewer에서 관찰되는 단열특성과 수리전도도와의 상관관계 분석

  • Park Gyeong-U;Bae Dae-Seok;Kim Gyeong-Su;Go Yong-Gwon
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • 2005.04a
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    • pp.284-287
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    • 2005
  • The flow of groundwater in fractured medium is related to the geometric characteristics of the fracture system. And a fracture aperture and a fracture density are considered as important factor concerning the permeability. Data acquisition of the properties of fracture such as aperture and density is so difficult and has uncertainty. We also cannot know the fracture characteristics through the in-situ tests. We usually obtain the fracture information from a ultrasonic scan logging or borehole television indirectly. Using the deduced results, we can make the fracture system and simulate the groundwater flow and solute transport in the crystalline rock. This study aimed to analyze the correlation between the properties of fracture and hydraulic conductivities obtained at the same interval. The properties of fracture are examined by acoustic televiwer and hydraulic conductivities are obtained by constant Pressure injection test. The distributioin of fracture width and fracture frequency shows the log-normal probability plot. And, Results of correlation analysis explain that opened type fractures have proper relation with hydraulic conductivity. But, as though there are semi-opened type fractures or closed type fractures, those have the permeable structure.

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Influence of ambient groundwater flow on DNAPL migration in a fracture network

  • 지성훈;여인욱;이강근
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • 2003.04a
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    • pp.43-46
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    • 2003
  • We consider influences of the aperture variation and the ambient groundwater flow on the migration of DNAPL within a fracture network. In context of a modified invasion percolation (MIP) growth algorithm, we formulate a mechanistic model that includes capillary and gravity forces as well as viscous forces within the DNAPL and the ambient groundwater. The MIP model is verified against laboratory experiments, which is conducted using a two-dimensional random fracture network model. The results show that the aperture variation and ambient groundwater flow can be significant factors controlling DNAPL migration path within fracture networks.

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Characterization of Fracture Transmissivity for Groundwater Flow Assessment using DFN Modeling (분리단열망개념의 지하수유동해석을 위한 단열투수량계수의 정량화 연구)

  • 배대석;송무영;김천수;김경수;김증렬
    • The Journal of Engineering Geology
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    • v.6 no.1
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    • pp.1-13
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    • 1996
  • The fracture transmissivity($T_f$) is the most important parameter of fracture in assessing groundwater flow in fractured rock masses by using the DFN(Discrete Fracture Network) modeling. $T_f$, the most sensitive parameter m DFN modeling, is dependent upon aperture, size and filling characteristics of each fracture set. In the field test, the accuracy of $T_f$ can be increased with Borehole Acoustic Scanning (Televiewer) and Fixed Interval Length(FIL) test in constant head. $T_f$ values measured from FIL test was modified and estimated by each fracture set on the basis of the Cubic Law and the information of aperture and filling characteristics obtained from Televiewer. The modified $T_f$ results in the increase of confidence and reliability of modeling results including the amount of tunnel inflow.And, this approach would reduce the uncertaintity of the assessment for groundwater flow in fractured rock masses using the DFN modeling.

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A Study of the Influence of Roughness on fracture Shear Behaviour and Permeability (거칠기가 절리의 전단거동 및 투수성에 미치는 영향에 관한 연구)

    • Tunnel and Underground Space
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    • v.12 no.4
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    • pp.312-320
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    • 2002
  • It is well-known that when single rock fractures undergo shear displacement, they are influenced by the boundary conditions and fracture roughness. In this case, aperture geometry will change by means of dilation due to the shear displacement. As fractures become the flow paths, fluid flow through rock fractures is affected by the void geometry. In this study, therefore, the influence of roughness on shear behavior of fractures has been investigated, and the resulting hydraulic behavior has been analyzed. In order for this study, a statistical method has been used to generate rough fractures, and they have been adopted into new conceptual models fur fracture shearing and flow calculations. The main contributions of this study are as follows: firstly, fracture shear behavior becomes less brittle with decreasing fracture roughness and increasing normal stress. Then, the characteristics of aperture distribution becomes those of roughness of fractures indicating its hydraulic significance. Finally, it is observed that with decreasing fracture roughness the breakdown of channel flow occurs more slowly.

Effect of Joint Aperture Variation on Hydraulic Behavior of the 2-D DFN System (절리간극의 변화가 이차원 DFN 시스템의 수리적 특성에 미치는 영향)

  • Han, Jisu;Um, Jeong-Gi
    • Tunnel and Underground Space
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    • v.26 no.4
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    • pp.283-292
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    • 2016
  • A computer program code was developed to estimate hydraulic behavior of the 2-D connected pipe network system, and implemented to evaluate the effect of joint aperture on hydraulic parameters of fractured rock masses through numerical experiments. A total of 216 stochastic 2-D DFN(discrete fracture network) blocks of $20m{\times}20m$ were prepared using two joint sets with fixed input parameters of joint orientation, frequency and size distribution. Two different cases of joint aperture variation are considered in this study. The hydraulic parameters were estimated for generated 2-D DFN blocks. The hydraulic anisotropy and the chance for equivalent continuum behavior of the DFN system were found to depend on the variability of joint aperture.

A Numerical Study on Characteristics of Fluid Flow in Rough Fractures with Spatial Correlation Length and Mechanical Effect (공간적 상관길이와 역학적 효과에 따른 거친 단일 균열 내의 유체 흐름에 관한 수치적 연구)

  • Jeong, Woochang
    • Journal of the Korean GEO-environmental Society
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    • v.8 no.4
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    • pp.27-39
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    • 2007
  • This paper investigates numerically characteristics of the fluid flow in spatially correlated variable-aperture fractures under effective normal stress conditions. Spatially correlated aperture distributions are generated by using the geostaistical method (i.e. Turning Bands algorithm). In order to represent a nonlinear relationship between the effective normal stress and the fracture aperture, a simple mechanical formula is combined with a local flow model. Obtained numerical results indicate that the fluid flow is significantly affected by the geometry of aperture distribution varying according to the applied effective normal stress as well as the spatial correlation length of aperture distribution. Moreover, by using results simulated in this study, the modified Louis formula representing the relationship between the effective normal stress and the effective permeability of fracture is proposed.

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Relation between Groundwater Inflow into the Waterway Tunnel and Hydrogeological Characteristics in Hyeonseo-myeon, Cheongsong-gun, Korea (청송군 현서면 일대 도수로터널내 지하수 유입량과 수리지질 특성의 관련성)

  • 박재현;함세영;성익환;이병대;정재열
    • The Journal of Engineering Geology
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    • v.11 no.2
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    • pp.141-152
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    • 2001
  • The waterway tunnel zone (length 1,484m) in the Hyeonseo-myeon area that is a part of Yeongcheon dam waterway tunnel has been studied to characterize the relationship between groundwater inflow into the waterway tunnel and hydrogeologic characteristics. The effects of sandstone thickness in the tunnel section. fracture density, fracture aperture and spacing, fault zone width and hydraulic conductivity on the early inflow (inflow prior to the lining and grouting) are investigated. The relationship between fracture density and hydraulic conductivity is also considered. The result of the study suggests that fault zone width has the greatest effect on groundwater inflow into the tunnel, and sandstone thickness, hydraulic conductivity and fracture density in order shows an influence on the inflow.

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