• Journal of Soil and Groundwater Environment
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• v.8 no.4
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• pp.1-11
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• 2003

In order to measure aperture variation dependent on normal stress and to characterize on relationship between aperture variation and hydraulic conductivity this study measured apertures of rock fractures under a high resolution confocal laser scanning microscope (CLSM) with application of five stages of uniaxial normal stresses. From this method the response of aperture can be continuously characterized on one specimen by different loads of normal stress. The results of measurements showed a rough geometry of fracture bearing non-uniform aperture. They also revealed different values of aperture variations according to the load stages on each position along a fracture due to the fracture roughness. Laboratory permeability tests were also conducted to evaluate the changes of permeability coefficients related to the aperture variations by different loads. The results of permeability tests revealed that the hydraulic conductivity was not reduced at a fixed rate with increase of normal load. Moreover, the rates of aperture variations did not match to those of hydraulic conductivity. The hydraulic conductivity calculated in this study did not follow the cubic law, representing that the parallel plate model is not suitable to express the fracture geometry corresponding to the results of aperture measurements under the CLSM.

• Nuclear Engineering and Technology
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• v.44 no.6
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• pp.639-652
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• 2012

A three-dimensional discrete fracture network model was developed in order to simulate the hydraulic characteristics of a granitic rock mass at Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT). The model used a three-dimensional discrete fracture network (DFN), assuming a correlation between the length and aperture of the fractures, and a trapezoid flow path in the fractures. These assumptions that previous studies have not considered could make the developed model more practical and reasonable. The geologic and hydraulic data of the fractures were obtained in the rock mass at the KURT. Then, these data were applied to the developed fracture discrete network model. The model was applied in estimating the representative elementary volume (REV), the equivalent hydraulic conductivity tensors, and the amount of groundwater inflow into the tunnel. The developed discrete fracture network model can determine the REV size for the rock mass with respect to the hydraulic behavior and estimate the groundwater flow into the tunnel at the KURT. Therefore, the assumptions that the fracture length is correlated to the fracture aperture and the flow in a fracture occurs in a trapezoid shape appear to be effective in the DFN analysis used to estimate the hydraulic behavior of the fractured rock mass.

• Tunnel and Underground Space
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• v.24 no.2
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• pp.176-186
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• 2014

Roughness, aperture and filling material of rock joint are widely considered to affect the hydraulic characteristics of joint. Among these factors, in this study, the joint roughness was examined with artificial joint profiles generated by Monte Carlo simulating on the original profiles suggested by Barton and Choubey(1977). Original profiles and revised profiles were combined to establish flow channel models, in which the hydraulic characteristics were analyzed numerically on the basis of minimum aperture changes and flow channel shapes. Maximum flow rate was identified at the growing point of flow area after passing through minimum aperture generated by the two profiles, and it was resulted that maximum flow rate is inversely proportional to minimum aperture. Maximum flow rate per unit area showed different values because flow channel shapes and minimum aperture locations are different in each model. In flow channel, mechanical aperture showed approximately 1.07 ~ 3.00 times larger than hydraulic aperture. In this study, mechanical and hydraulic aperture were concluded to be closely related to $A_i$ value, and their relations can be denoted by $e_m=0.519A^{0.7169_i}$ and $e_h=0.6182A^{0.239}_i$, respectively.

• 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.

• Tunnel and Underground Space
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• v.10 no.1
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• pp.45-58
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• 2000

Cyclic shear test system, which is capable of measuring flow rate inside rock joint, was established to investigate the hydraulic behavior of rough rock joints under various loading conditions. Laboratory hydraulic tests during compression and shear were conducted for artificial rough rock joints. Prior to tests, aperture characteristics of specimens were examined by measuring surface topography. Permeability changes under compression were well approximated with several hydraulic model. Hydraulic behavior conformed to dilation characteristics in the first stage, and permeability increased with increase of dilation. As the shear displacement progressed, flow rate became somewhat constant due to gouge production and offset of apertures. Hydraulic behavior under cyclic shear loading was also influenced by the degradation of asperities and gouge production. In addition. the relation between hydraulic aperture and mechanical aperture under compression and shear loading was investigated and compared.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.328-336
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• 1999

To characterize the hydro-mechanical behavior of a rock joint, a rotary shear testing apparatus was devised in this study. Shear stress was driven by twisting the end of a sample in the rotary shear testing apparatus. The test results show that the rotary shear test underestimates the peak shear strength of a rock joint. The torque is known as a function of the radial distance from the axis of rotation, resulting in the radial variation of the shear stress. Fluid flow through rock joints is mainly dependent on the Joint roughness, contact area, initial aperture. To examine the dependency, the relationship between the hydraulic and the mechanical apertures for shear-flow was established by measuring the initial aperture. It shows that the mechanical aperture and the hydraulic aperture increase linearly with the dilatancy. The difference between the hydraulic and mechanical apertures describes the deviation from the behavior predicted by the parallel plate model.

• 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.

• Nuclear Engineering and Technology
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• v.42 no.1
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• pp.9-16
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• 2010

Experimental examinations for evaluating fracutres were conducted by using transparent replicas of a single fracture in order to obtain the fracture data to contribute to the methodlogy on how to improve the definitaion of representative parameter values used for a parallel plate fracture model. Quantitative aperture distribution and quantitative tracer concentration data at each point in time were obtained by measuring the attenuation of transmitted light through the fracture in high spatial resolution. the representative aperture values evaluated from the multiple different measurement methods, such as arithmetic mean of aperture distribution measured by the optical method, transport aperture evaluated from the tracer test, and average aperture evaluated from the fracture void volume measurement converged to a unique value that indicates the accuracy of this experimental study. The aperture data was employed for verifying the numerical simulation under the assuption of Local Cubic Law and showed that the calculated flow rate through the fracture is 10%-100% larger than hydraulic test results. The quantitative tracer concentration data is also very valuable for validating existing numerical code for advection dispersion transport in-plane heterogeneous fractures.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.133-141
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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 processes induced by the excavation. Various studies have been carried out on EDZ, but most studies have 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 zone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation by using H-M coupling analysis. Fundamental principles of distinct element method (DEM) were used in the analysis. In the same groundwater level, the behavior of hydraulic aperture near the cavern was analyzed for different stress ratios, initial apertures, fracture angles and fracture spacings by using a two-dimensional DEM program. We evaluate the excavation induced hydraulic aperture change. Using the results of the study, hydraulic EDZ was defined as an elliptical shape model perpendicular to the joint.

• The Journal of Engineering Geology
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• v.12 no.2
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• pp.151-166
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• 2002

Groundwater development as a means of acquiring subsidiary water resource is very important for the persistent security of water resource. Nowadays, pneumatic fracturing technology which was developed in the advanced countries is applied for increasing pumping rate and eliminating contaminants. This study gives an experimental data to clarify permeability characteristics of the single discontinuity which is newly developed or increased in aperture by the pneumatic fracturing or damage propagation of the natural barrier for the nuclear waste disposal. On the basis of understanding the relationship between permeability and hydraulic aperture the result could apply as one of the basic data for researches concerned with increasing pumping rate and eliminating contaminants. Hydraulic aperture is decreased exponentially with increasing confining pressure and proportioned to permeability in the same confining pressure. Especially, with the increasing aperture permeability of coarse- and medium- grained granite shows the more rapid increasing than that of fine- grained granite.