• Tunnel and Underground Space
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• v.32 no.6
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• pp.568-585
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• 2022

In the present study, we proposed a numerical method for simulating thermally induced fracture slip using a grain-based distinct element model (GBDEM). As a part of DECOVALEX-2023, the thermo-mechanical loading test on a saw-cut rock fracture conducted at the Korea Institute of Civil Engineering and Building Technology was simulated. In the numerical model, the rock sample including a saw-cut fracture was represented as a group of random Voronoi polyhedra. Then, the coupled thermo-mechanical behavior of grains and their interfaces was calculated using 3DEC. The key concerns focused on the temperature evolution, thermally induced principal stress increment, and fracture normal and shear displacements under thermo-mechanical loading. The comparisons between laboratory experimental results and the numerical results revealed that the numerical model reasonably captured the heat transfer and heat loss characteristics of the rock specimen, the horizontal stress increment due to constrained displacement, and the progressive shear failure of the fracture. However, the onset of the fracture slip and the magnitudes of stress increment and fracture displacement showed discrepancies between the numerical and experimental results. 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.

• Economic and Environmental Geology
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• v.34 no.5
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• pp.447-460
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• 2001

The geothermal waters from the Busan area belong to Na-CI type and are characterized by much higher EC (921 ~6,520${\mu}$S/cm) and TDS (608-3,390 mg/L) than other geothermal waters in Korea. The concentration of majorions shows a weakly positive relationship with temperature except for Mg ion. The concentrations of the major cat ions have the order of Na>Ca>K>Mg. Ca ion is enriched and Mg ion is depleted compared with seawater. All Br concentrations of geothermal water are lower than those of seawater, showing a positive relationship with temperature. Generally geochemical characteristics of geothermal waters of the Busan area indicate that these waters have relatively increased Ca and Sr contents and depleted Mg, Na and K contents caused by seawater interaction with wall rock at depth during deep circulation of seawater. Base on the relationship between major ions and temperature, saline geothermal waters are diluted and are cooled by mixing of groundwaters during ascent. Isotope study and reaction path modeling of the overall geochemical system are required in order to better quantify the evolution and origin of geothermal waters in the Busan area.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.211-221
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• 2003

At Aspo hard rock laboratory in Sweden, an in-situ heater experiment called "$\"{A}"{s}"{p}"{o}$ Pillar Stability Experiment (APSE)" is prepared to assess capability to predict spatting and stability in a rock mass between deposition holes for radioactive waste. To Predict reasonably fracturing process at rock pillar under a planned configuration before testing, a boundary element code FRACOD has been applied for modelling. The code has been improved to simulate explicitly fracture evolution both at rock boundaries and in intact rocks. A new inverse stress reconstruction technique using boundary element has been also developed to transfer stress field by excavation and thermal loading into the FRACOD model. This article presents the results from predictive modelling far the planned in-situ test condition. Excavation induced stresses might cause slight fracturing in the pillar walls. Typical shear fractures have been initiated and propagated near central pillar walls during 120 days of heating, but overall rock mass remained stable under the considered configuration. The effects of pre-existing joints and properties of fractures are also discussed. It is found from the results that FRACOD can properly model essential rock spatting and propagation at deep tunnels and boreholes.at deep tunnels and boreholes.

• The Journal of Engineering Geology
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• v.33 no.1
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• pp.39-49
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• 2023

Soil contaminants measured and managed in Korea include those of geologic origin such as arsenic, cadmium, copper, lead, zinc, nickel, mercury, and fluoride. This study identifies the distribution of these contaminants using GIS modeling to analyze the spatial probability of soil contamination originating from geology. The modeling found that cadmium, copper, lead, nickel, and mercury often exceed the regulated standard by <1%. Concentrations of arsenic and zinc greatly exceeded the standard in the vicinity of mines and industrial complexes: mining and industry seemed to have substantial effects on the concentrations of these metals. Although fluoride was sampled at the lowest number of points, its frequency of exceeding the standard was the highest. No obvious source of artificial contamination has been identified, and fluoride's distribution characteristics showed continuity over a wide area, suggesting a strong correlation between geological characteristics and fluoride concentration. The highest frequencies of fluoride exceeding the standard were in Jurassic granite (40.00%) and Precambrian banded gneiss (34.12%). As these rocks contributed to the formation of soil through their weathering, high fluoride concentrations can be expected in soil in areas where these rocks are distributed.

• Explosives and Blasting
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• v.33 no.1
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• pp.13-20
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• 2015

Recently, as the demand for development and utilization of underground space is increasing worldwide, the blast damaged zone has become a major issue in constructing underground structures. In this study, numerical analyses were performed for modelling a small-scale blasting of rock plates using PFC3D and ANSYS LS-DYNA. In order to verify the analysis results, several test blasts were conducted. It is concluded from the study that the numerical modelling methods well simulate the crack propagation procedure near blast holes under given conditions.

• The Journal of the Petrological Society of Korea
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• v.13 no.4
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• pp.214-223
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• 2004

Oxygen and hydrogen isotopic compositions of the Jurassic peraluminous Hwacheon granite were measured, and compared with those of other Jurassic peraluminous Daebo granite in Korea. $\delta$$\^$18/O values for quartz and feldspar of the Hwacheon granite range from 8.2 to 10.6 and 5.8 to 9.0$\textperthousand$, respectively. Whole rock $\delta$$\^$18/O values for banded biotite gneiss country rocks surrounding the Hwacheon granites range from 8.1 to 9.4$\textperthousand$. Whole rock and biotite $\delta$D Values for Hwacheon granite range from -84 to -113 and -107 to -113$\textperthousand$, respectively. Whole rock $\delta$D values for banded biotite gneiss country rocks range from -76 to -100$\textperthousand$. Both $\delta$$\^$18/O and $\delta$D values of the Hwacheon granite are characterized by low values compared to the 'normal' values for the fresh peraluminous granitic rocks. Low $\delta$$\^$18/O values of the Hwacheon granite resulted from fluid-rock interaction for a long period. Isotopic modelling result renders that a relatively low-$\delta$$\^$18/O fluid below -1$\textperthousand$ was involved in subsolidus isotopic exchange under a relatively high fluid/rock ratio (<-6). The fluid of meteoric origin has experienced a modification of oxygen isotopic composition as a result of fluid-rock interaction with the Hwacheon granite and surrounding metapelitic country rocks.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.4
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• pp.273-281
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• 2007

Hyperalkaline groundwater formed by groundwater-cement components and its reaction with bedrock in a nuclear waste repository were simulated by geochemical modeling. The result of groundwater-cement components reaction showed that the pH of water was 13.3 and the precipitated minerals were Brucite, Katoite, Calcium Silicate Hydrate(CSH1.1), Ettringite, Hematite, and Portlandite. The result of interaction between such minerals and groundwater sampled in Gyeongju area also showed that the pH of groundwater reached 12.4. Interaction between such hyperalkaline groundwater and granite was simulated by kinetic model during $10^3$ years. This result showed that the final pH of groundwater reached 11.2 and the variation of pH was controlled by dissolution/precipitation of silicate and CSH minerals. Groundwater quality was also determined by dissolution/precipitation of silicate, CSH, oxide minerals. Our results show that geochemical modeling of long-term hyperalkaline groundwater and rock interaction can contribute to the safety assessment of engineered barrier by predicting geochemical condition in repository site.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.3
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• pp.263-273
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• 2007

When a tunnel or an underground structure is excavated in deep geological environments, the failure process is affected and eventually dominated by stress-induced fractures growing preferentially parallel to the excavation boundary. This fracturing is generally referred to as brittle failure by spatting and slabbing. Continuum models with traditional failure criteria such as Hoek-Brown or Mohr-Coulomb criteria have not been successful in prediction of the extent and depth of brittle failure. Instead cohesion weakening and frictional strengthening (CWFS) model is known to predict brittle failure well. In this study, CWFS model was applied to predict the brittle failure around a circular opening observed in physical model experiments. To obtain the input parameters for CWFS model, damage-controlled tests were carried out. The predicted depth and extent of brittle failure using CWFS model were compared to the results of the physical model experiment and numerical simulation using traditional model.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.282-283
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• 1999

핵폐기물 지하처분, 지열개발, 지하 환경의 안전과 제어 등과 관련된 문제에 있어서 암석 및 암반의 역학적 거동 외에 열·수리·화학적 상호작용에 대한 이해가 필요하다. 이미 전세계적으로 국가별로 혹은 공동연구를 통하여 열·수리·역학적 상호작용에 관하여 많은 연구가 진행되었으며 최근 화학적 상호작용에 대한 문제가 추가적으로 제기되고 있다. 특히 장기간의 지하 환경의 안정성에 미치는 중요한 요소로 크립현상과 열·수리 화학적 상호작용 연구에 대한 필요성이 제기된 바 있다. 이 중 열·역학적 상호작용에 대해서는 현장문제에 적용 가능한 만은 연구결과가 제시된 바 있으나 기타 상호작용에 대해서는 다양한시험방법과모델링으로 인하여 아직가지 통일된 의견이 제시된 바 없다. 제 2주제에는 총 92편의 논문이 접수되었으며, 이 논문들의 내용, 성격, 해석방법 등을 간략히 정리하였다.

• Geophysics and Geophysical Exploration
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• v.9 no.3
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• pp.241-249
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• 2006

Due to the long tectonic history and the very complex geologic formations in Korea, the anisotropic characteristics of subsurface material may often change very greatly and locally. The algorithms commonly used, however, may not give sufficiently precise computational results of traveltime data particularly for the complex and strong anisotropic model, since they are based on the two-dimensional (2D) earth and/or weak anisotropy assumptions. This study is intended to develope a three-dimensional (3D) modeling algorithm to precisely calculate the first arrival time in the complex anisotropic media. Considering the complex geology of Korea, we assume 3D TTI (tilted transversely isotropy) medium having the arbitrary symmetry axis. The algorithm includes the 2D non-linear interpolation scheme to calculate the traveltimes inside the grid and the 3D traveltime mapping to fill the 3D model with first arrival times. The weak anisotropy assumption, moreover, can be overcome through devising a numerical approach of the steepest descent method in the calculation of minimum traveltime, instead of using approximate solution. The performance of the algorithm developed in this study is demonstrated by the comparison of the analytic and numerical solutions for the homogeneous anisotropic earth as well as through the numerical experiment for the two layer model whose anisotropic properties are greatly different each other. We expect that the developed modeling algorithm can be used in the development of processing and inversion schemes of seismic data acquired in strongly anisotropic environment, such as migration, velocity analysis, cross-well tomography and so on.