• Journal of Korean Tunnelling and Underground Space Association
• /
• v.25 no.2
• /
• pp.175-186
• /
• 2023

The buffer materials in disposal hole are exposed to the decay heat from spent nuclear fuels and groundwater inflow through adjacent rockmass. Since understanding of thermal-hydro-mechanical-chemical (T-H-M-C) interaction in buffer material is crucial for predicting their long-term performance and safety of disposal repository, it is necessary to investigate the heating-hydration characteristics and consequent T-H-M-C behavior of the buffer materials under disposal conditions considering geochemical factors. In response, the Korea Atomic Energy Research Institute developed a laboratory-scale 'Lab.THMC' experiment system, which characterizes the T-H-M behavior of buffer materials under different geochemical conditions by analyzing heating-hydration process and stress changes. This technical report introduces the detail design of the Lab.THMC system, summarizes preliminary experimental results, and outlines future research plans.

• The Journal of Engineering Geology
• /
• v.31 no.1
• /
• pp.55-66
• /
• 2021

Hydraulic-mechanical (H-M) coupled numerical modeling was used to evaluate the evolution of hydrogeological properties in response to the installation and expansion of a borehole. A domain with a discrete fracture network was adopted for discontinuum modeling to simulate changes in fracture apertures. Comparison with real hydraulic test data shows that the effects of principal stress direction and expansion of borehole diameter were reasonably simulated by H-M coupled numerical modeling. The modeling confirmed that aperture changes depended on the principal stress direction, with an increase in aperture size due to vertical displacement being the dominant effect. A concentration of shear dilation around the borehole had an additional, subsidiary, effect on the hydrogeological evolution. These results show that the permeability of fractured rock can be increased by changing the hydraulic properties of a fracture through stress redistribution caused by the installation and expansion of a borehole.

• Tunnel and Underground Space
• /
• v.30 no.4
• /
• pp.306-319
• /
• 2020

Characterizations of Excavation Damage Zone (EDZ), which is hydro-mechanical degrading the host rock, are the important issues on the geological repository for the spent nuclear fuel. In the DECOVALEX 2019 project, Task G aimed to model the fractured rock numerically, describe the hydro-mechanical behavior of EDZ, and predict the change of the hydraulic factor during the lifetime of the geological repository. Task G prepared two-dimensional fractured rock model to compare the characteristics of each simulation tools in Work Package 1, validated the extended three-dimensional model using the TAS04 in-situ interference tests from Äspö Hard Rock Laboratory in Work Package 2, and applied the thermal and glacial loads to monitor the long-term hydro-mechanical response on the fractured rock in Work Package 3. Each modelling team adopted both Finite Element Method (FEM) and Discrete Element Method (DEM) to simulate the hydro-mechanical behavior of the fracture rock, and added the various approaches to describe the EDZ and fracture geometry which are appropriate to each simulation method. Therefore, this research can introduce a variety of numerical approaches and considerations to model the geological repository for the spent nuclear fuel in the crystalline fractured rock.

• Tunnel and Underground Space
• /
• v.24 no.2
• /
• pp.176-186
• /
• 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
• /
• v.9 no.1
• /
• pp.1-11
• /
• 1999

A finite element code was developed to analyze coupled thermo-hydro-mechanical phenomena. This code is based on the finite element formulation provided by Noorishad et al. (1984) and Joint behavior was simulated Goodman's joint constitutive model. The developed code was applied for T-H-M coupling analysis for two kinds of shaft models, with a joint or without a joint respectively. For a model without a joint, temperature increased from the shaft wall to outward evidently. The radial displacement showed opposite directions of outward and inward at some distance from shaft wall. For a model with a joint, closure of joint was found due to thermal expansion. The temperature distribution along a joint showed relatively lower than that of rock matrix because of low thermal conductivity and high specific heat of water. And it could be concluded that effects of thermal flow to joint were more than that of hydraulic flow in a rock mass.

• Proceedings of the Korean Society for Rock Mechanics Conference
• /
• 2003.03a
• /
• pp.43-50
• /
• 2003

• Journal of the Korean Geotechnical Society
• /
• v.38 no.9
• /
• pp.45-52
• /
• 2022

Because discontinuity in the rock mass and contact of soil-structure interaction exhibits coupled thermal-hydromechanical (THM) behavior, it is necessary to develop an interface element based on the full governing equations. In this study, we derive force equilibrium, fluid continuity, and energy equilibrium equations for the interface element. Additionally, we present a stiffness matrix of the elastoplastic mechanical model for the interface element. The developed interface element uses six nodes for displacement and four nodes for water pressure and temperature in a two-dimensional analysis. The fully coupled THM analysis for fluid injection into a fault can model the complicated evolution of injection pressure due to decreasing effective stress in the fault and thermal contraction of the surrounding rock mass. However, the result of hydromechanical analysis ignoring thermal phenomena overestimates hydromechanical variables.

• Tunnel and Underground Space
• /
• v.29 no.3
• /
• pp.197-213
• /
• 2019

We simulated the fault reactivation experiment conducted at 'Main Fault' intersecting the low permeability clay formations of Mont Terri Underground Research Laboratory in Switzerland using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. We formulate the hydro-mechanical coupling relation of hydraulic aperture to consider the elastic fracture opening and failure-induced dilation for reproducing the abrupt changes in injection flow rate and monitoring pressure at fracture opening pressure. A parametric study was conducted to examine the effects of in-situ stress condition and fault deformation and strength parameters and to find the optimal parameter set to reproduce the field observations. In the best matching simulation, the fracture opening pressure and variations of injection flow rate and monitoring pressure showed good agreement with field experiment results, which suggests the capability of the numerical model to reasonably capture the fracture opening and propagation process. The model overestimated the fault displacement in shear direction and the range of reactivated zone, which was attributed to the progressive shear failures along the fault at high injection pressure. In the field experiment results, however, fracture tensile opening seems the dominant mechanism affecting the hydraulic aperture increase.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.20 no.2
• /
• pp.168-175
• /
• 2008

In this study, we estimated the discharge capacity of Solicheon sluice gate in Gunjang national industrial complex by hydraulic physical scale model test and FLOW-3D. It was showed that the discharge capacity of gate carried by physical model test and numerical analysis was similar.

• Tunnel and Underground Space
• /
• v.29 no.6
• /
• pp.468-479
• /
• 2019

It is essential to comprehend coupled hydro-mechanical behavior to utilize subsurface for the recent demand for underground space usage. In this study, we developed a new simulator for numerical simulation as a tool for researching to consider the various domestic field and subsurface conditions. To develop the new module, we combined OpenGeoSys, one of the scientific software package that handles fluid mechanics (H), thermodynamics (T), and rock and soil mechanics (M) in the subsurface with FLAC3D, one of the commercial software for geotechnical engineering problems reinforced. In this simulator development, we design OpenGeoSys as a master and FLAC3D as a slave via a file-based sequential coupling. We have chosen Terzaghi's consolidation problem related to single-phase fluid flow at a saturated condition as a benchmark model to verify the proposed module. The comparative results between the analytical solution and numerical analysis showed a good agreement.