• Tunnel and Underground Space
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• v.32 no.2
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• pp.144-159
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• 2022

The present study developed a sequential approach-based numerical simulator for modeling coupled thermal-hydrological-mechanical (THM) processes in the ground and investigated the computational performance of the coupling analysis algorithm. The present sequential approach linked the two different solvers: an open-source numerical code, OpenGeoSys for solving the thermal and hydrological processes in porous media and a commercial code, FLAC3D for solving the geomechanical response of the ground. A benchmark test of the developed simulator was carried out using a THM problem where an analytical solution is given. The benchmark problem involves the coupled behavior (variations in temperature, pore pressure, stress, and deformation with time) of a fully saturated porous medium which is subject to a point heat source. The results of the analytical solution and numerical simulation were compared and the validity of the numerical simulator was investigated.

• Tunnel and Underground Space
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• v.21 no.1
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• pp.66-81
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• 2011

In this study, it was aimed to develop a thermal-hydraulic-mechanical coupled fracture mechanics code that models a fracture initiation, propagation and failure of underground rock mass due to thermal and hydraulic loadings. The development was based on a 2D FRACOD (Shen & Stephasson, 1993), and newly developed T-M and H-M coupled analysis modules were implemented into it. T-M coupling in FRACOD employed a fictitious heat source and time-marching method, and explicit iteration method was used in H-M coupling. The validity of developed coupled modules was verified by the comparison with the analytical result, and its applicability to the fracture initiation and propagation behavior due to temperature changes and hydraulic fracturing was confirmed by test simulations.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.155-167
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a high-temperature cavern thermal energy storage (CTES) operated for a period of 30 years has been investigated by TOUGH2-FLAC3D simulator. As a fundamental study for the development of prediction and control technologies for the environmental change and rock mass behavior associated with CTES, the key concerns were focused on the hydrological-thermal multiphase flow and the consequential mechanical behavior of the surrounding rock mass, where the insulator performance was not taken into account. In the present study, we considered a large-scale cylindrical cavern at shallow depth storing thermal energy of $350^{\circ}C$. The numerical results showed that the dominant heat transfer mechanism was the conduction in rock mass, and the mechanical behavior of rock mass was influenced by thermal factor (heat) more than hydrological factor (pressure). The effective stress redistribution, displacement and surface uplift caused by heating of rock and boiling of ground-water were discussed, and the potential of shear failure was quantitatively examined. Thermal expansion of rock mass led to the ground-surface uplift on the order of a few centimeters and the development of tensile stress above the storage cavern, increasing the potential of shear failure.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.175-184
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• 2008

In this study, state-of-the-art of $CO_2$ geological sequestration as a method of greenhouse gas reduction was reviewed. Thermal-Hydraulic-Mechanically(THM) coupled simulation technology and its application to a stability analysis of geological formation due to $CO_2$ injection as well as a leakage path analysis were investigated and introduced.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.168-185
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a large-scale high-temperature cavern thermal energy storage (CTES) at a shallow depth has been investigated, and the effects of hydrological conditions such as water table and rock permeability on the behavior have been examined. The liquid saturation of ground water around a storage cavern may have a small impact on the overall heat transfer and mechanical behavior of surrounding rock mass for a relatively low rock permeability of $10^{-17}m^2$. In terms of the distributions of temperature, stress and displacement of the surrounding rock mass, the results expected from the simulation with the cavern below the water table were almost identical to that obtained from the simulation with the cavern in the unsaturated zone. The heat transfer in the rock mass with reasonable permeability ${\leq}10^{-15}m^2$ was dominated by the conduction. In the simulation with rock permeability of $10^{-12}m^2$, however, the convective heat transfer by ground-water was dominant, accompanying the upward heat flow to near-ground surface. The temperature and pressure around a storage cavern showed different distributions according to the rock permeability, as a result of the complex coupled processes such as the heat transfer by multi-phase flow and the evaporation of ground-water.

• Tunnel and Underground Space
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• v.34 no.2
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• pp.127-142
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• 2024

The robustness of a numerical method means that its computational performance is maintained under various modeling conditions. New numerical methods or codes need to be assessed for robustness through benchmark testing. The TOUGH-FLAC modeling approach has been applied to various fields such as subsurface carbon dioxide storage, geological disposal of spent nuclear fuel, and geothermal development both domestically and internationally, and the modeling validity has been examined by comparing the results with experimental measurements and other numerical codes. In the present study, a benchmark test of the TOUGH-FLAC approach was performed based on a coupled thermal-hydro-mechanical behavior problem with an analytical solution. The analytical solution is related to the temperature, pore water pressure, and mechanical behavior of a fully saturated porous medium that is subjected to a point heat source. The robustness of the TOUGH-FLAC approach was evaluated by comparing the analytical solution with the results of numerical simulation. Additionally, the effects of thermal-hydro-mechanical coupling terms, fluid phase change, and timestep on the computation of coupled behavior were investigated.

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

• Journal of the Korean Geotechnical Society
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• v.38 no.9
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• pp.45-52
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• 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
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• v.25 no.6
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• pp.556-567
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• 2015

The evaluation of THM coupling behavior in deep underground repository condition is essential for the long term safety and stability assessment of high-level radioactive waste repository. In order to develop reliable THM analysis techniques effectively, an international cooperation project, DECOVALEX, is carried out. In DECOVALEX-2015 Task B2, the in situ THM experiment planned to be conducted by JAEA was modeled by the research teams from the participating countries. In this study, a THM coupling technique combining TOUGH2 and FLAC was developed and applied to 1 dimensional THM modeling, in which rock, buffer, and heater are considered. The results were compared with those from other research teams.

• Journal of the Korean GEO-environmental Society
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• v.24 no.9
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• pp.41-46
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• 2023

Numerical analysis of frost heave is challenging due to the influence of soil and environmental factors. Thermo-hydromechanical coupled analysis relies heavily on excessive input variables and primarily focuses on validating clayey soils, so it is limited to frost susceptible silty soils. An empirical approach based on thermodynamics offers relatively simple frost heave analysis and the advantage of linking constitutive equations with frost heave to enable geomechanical interpretations. In this paper, we introduce an empirical numerical model using the Segregation Potential (SP) and evaluate reliability through comparative analysis with experimental results of frost susceptible silty soils. While the SP model enables frost heave analysis for the given silty soils, further investigation on various silty soils is necessary to gather data on key input variables.