• Tunnel and Underground Space
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• v.13 no.6
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• pp.465-475
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• 2003

Groundwater inflow into the caverns constructed in fractured rock mass was simulated by numerical modeling, NAPSAC (DFN, discrete fracture network model) and NAMMU (CPM, continuous porous media model), a finite-element software package for groundwater flow in 3D fractured media developed by AEA Technology, UK. The input parameters for modeling were determined on surface fracture survey, core logging and single hole hydraulic test data. In order to predict the groundwater inflow more accurately, the anisotropic hydraulic conductivity was considered. The anisotropic hydraulic conductivities were calculated from the fracture network properties. With a minor adjustment during model calibration, the numerical modeling is able to reproduce reasonably groundwater inflows into cavern and the travel length and times to the ground surface along the flow paths in the normal, dry and rainy seasons.

• Journal of Korea Water Resources Association
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• v.31 no.3
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• pp.347-360
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• 1998

Numerical simulations for fluid flow and solute transport in a fracture rock masses are performed by using a transient flow model, which is based on the three-dimensional stochastic and discrete fracture network model (DFN model) and is coupled hydraulic model with mechanical model. In the numerical simulations of the solute transport, we used to the particle following algorithm which is similar to an advective biased random walk. The purpose of this study is to predict the response of the tracer test between two deep bore holes (GPK1 and GPK2) implanted at Soultz sous Foret in France, in the context of the geothermal researches.l The data sets used are obtained from in situcirculating experiments during 1995. As the result of the transport simulation, the mean transit time for the non reactive particles is about 5 days between two bore holes.

• Water Engineering Research
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• v.6 no.2
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• pp.49-61
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• 2005

This paper presents the numerical study to examine characteristics of fluid flow and solute transport in a rough fracture subject to effective normal stresses. The aperture distribution is generated by using the self-affine fractal model. In order to represent a nonlinear relationship between the supported normal stress and the fracture aperture, we combine a simple mechanical model with the local flow model. The solute transport is simulated using the random walk particle following algorithm. Results of numerical simulations show that the flow is significantly affected by the geometry of aperture distribution varying with the effective normal stress level while it is slightly affected by the fractal dimension that determines the degree of the fracture surface roughness. However, solute transport is influenced by the effective normal stress as well as the fracture surface roughness.

• Journal of Korea Water Resources Association
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• v.52 no.2
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• pp.149-161
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• 2019

In this study, the effect of the fluid flow characteristics on the length distribution of the fracture elements composing the fracture network is analyzed numerically using the 3D fracture crack network model. The truncated power-law distribution is applied to generate the length distribution of the fracture elements and the simulations of fluid flow are carried out with the exponent ${\beta}_l$ from 1.0 to 6.0. As a result of simulations, when the exponent ${\beta}_l$ increases, the length distribution of the fracture elements gradually decreases, and the connectivity between the fracture elements affecting the permeability of the fracture network becomes weak. When we analyzed the distributions of flow rate calculated at each fracture element with the exponent ${\beta}_l$, the mean flow rate at ${\beta}_l=1.0$ was estimated to be about 447 times larger than that at ${\beta}_l=6.0$ and for the flow calculated at the outflow boundary of the fracture network, the case of ${\beta}_l=1.0$ was estimated to be 6,440 times larger than that of ${\beta}_l=6.0$.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.21-34
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• 2018

Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical parameters of several discontinuity sets related to the surrounding rock mass of Rudbar Lorestan Pumped Storage Power Plant powerhouse cavern making use of the linear and areal (circular and rectangular) sampling methods. Taking into consideration quite a large quantity of scanline and the window samplings used in this research, it was realized that the areal sampling methods are more time consuming and cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties related to four sets of discontinuities were computed. There is an acceptable difference among the mean trace lengths measured using two linear and areal methods for the two joint sets. A 3D discrete fracture network generation code (3DFAM) has been developed to model the fracture network based on the mapped data. The code has been validated on the basis of numerous geometrical characteristics computed by use of the linear, areal sampling methods and volumetric method. Results of the linear sampling method have significant variations. So, the areal and volumetric methods are more efficient than the linear method and they are more appropriate for validation of 3D DFN (Discrete Fracture Network) codes.

• 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.

• The Journal of Engineering Geology
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• v.20 no.4
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• pp.425-436
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• 2010

We established a stochastic 3-D fracture network system for fractured rock masses located in Il-Gwang Mine, Busan, to explore the relationship between the acidity of mine drainage and fracture geometry. A field scanline survey and borehole image processing were performed to estimate the best probability distributions of fracture geometry parameters. The stochastic 3-D fracture network system constructed for the rock masses was validated and deemed to be successful. The 3-D fracture network model was suitable for developing conceptual ideas on fluid flow in fractures at a field experimental site. An injection well and three observation wells were drilled at the field experimental site to monitor the acidity of mine drainage induced by the injection of fresh water. The field experiment, which was run for 29 days, yielded a significant relationship (with a high coefficient of determination) between the fracture geometry parameters and the acidity of mine drainage. The results show that pH increased with increasing relative frequency of fracture strike, and decreased with increasing fracture density. The concentration of $SO^{2-}_4$ decreased with increasing relative frequency of fracture strike, and increased with increasing fracture density.

• Tunnel and Underground Space
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• v.31 no.4
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• pp.270-288
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• 2021

We proposed a numerical method to simulate the hydro-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) in the paper. As a part of DECOVALEX-2023 Task G, we verified the method via benchmarks with analytical solutions. DECOVALEX-2023 Task G aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as a group of tetrahedral grains and calculated the interaction of the grains and their interfaces using 3DEC. The micro-parameters of the grains and interfaces were determined by a new methodology based on an equivalent continuum approach. In benchmark modeling, a single fracture embedded in the rock was examined for the effects of fracture inclination and roughness, the boundary stress condition and the applied pressure. The simulation results showed that the developed numerical model reasonably reproduced the fracture slip induced by boundary stress condition, the fracture opening induced by fluid injection, the stress distribution variation with fracture inclination, and the fracture roughness effect. In addition, the fracture displacements associated with the opening and slip showed good agreement with the analytical solutions. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Tunnel and Underground Space
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• v.6 no.1
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• pp.30-38
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• 1996

A two dimensional analysis program for groundwater flow in fractured network was developed to analyze the influence of discontinuity characteristics on groundwater flow. This program involves the generation of discontinuities and also connectivity analysis. The discontinuities were generated by the probabilistic density function(P.D.F.) reflecting the characteristics of discontinuities. And the fracture network model was completed through the connectivity analysis. This program also involves the analysis of groundwater flow through the discontinuity network. The result of numerical experiment shows that the equivalent hydraulic conductivity increased and became closer to isotropic as the density and trace length increased. And hydraulic head decreased along the fracture zone because of much water-flow. The grouting increased the groundwater head around cavern. An analysis of groundwater flow through discontinuity network was performed around underground oil storage cavern which is now under construction. The probabilistic density functions(P.D.F) were obtained from the investigation of the discontinuity trace map. When the anisotropic hydraulic conductivity is used, the flow rate into the cavern was below the acceptable value to maintain the hydraulic containment. But when the isotropic hydraulic conductivity is used, the flow rate was above the acceptable value.

• Journal of the Korean Society of Groundwater Environment
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• v.6 no.3
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• pp.111-119
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• 1999

The purpose of this study is the simulation of discontinuous rockmass and identification of characteristics of discontinuity network as a branch of the study on characteristics of groundwater system in discontinuous rockmass for evaluation of safety on disposal site of radioactive waste. In this study the site for LPG underground storage was selected for the similarities of the conditions which were required for disposal site of radioactive waste. Through the identification of hydraulic properties. characteristics of discontinuities and selection of discontinuity model around LPG underground storage facility. the applications of discrete fracture network model were evaluated for the analysis of pathway. The orientation and spatial density of discontinuities are primarily important elements for the simulation of groundwater and solute transportation in discrete fracture network model. In this study three fracture sets identified and the spatial intensity (P$_{32}$) of discontinuities is revealed as 0.85 $m^2$/㎥. The conductive fracture intensity (P$_{32c}$) estimated for the simulation area around propane cavern (200${\times}$200${\times}$200) is 0.536 $m^2$/㎥. Truncated conductive fracture intensity (T-P$_{32c}$) is calculated as 0.26 $m^2$/㎥ by eliminating the fracture with the iowest transmissivity and based on this value the pathway from the water curtain to PC 2. PC 3 analyzed.