• Tunnel and Underground Space
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• v.1 no.2
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• pp.218-228
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• 1991

Natural stress measurements have been made at two sites at the depth of 280m from surface by means of stress relief overcoring methods using three directonal deformation gage. Attempts have been made to determine the state of natural stress in the rock and provide useful basic data to investigate the stress distribution and the determination of yield zone around powerhouse cavern. The magnitude and the direction of the miximum principal stress obstained from in-situ stress measurements is -96.1kgf/$\textrm{cm}^2$ and N38$^{\circ}$W, N35$^{\circ}$W respectively. Vertical stresses are in approximately agreement with the theoretical value. The ratio of measured to theoretical stresses are 85% at two sites. The ratio of average horizontal to vertical stresses(k=($\sigma$h)ave/$\sigma$v is 1.07.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.184-193
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• 1998

In order to dispose radioactive wastes safely, it is needed to understand the mechanical, thermal, fluid behavior of rockmass and physico-chemical interactions between rockmass and water. Also, the knowledge about mechanical and hydraulic properties of rocks is required to predict and to model many conditions of geological structure, underground in-situ stress, folding, hot water interaction, intrusion of magma, plate tectonics etc. This study is based on researches about rock mechanics issues associated with a waste disposal in deep rockmass. This paper includes the mechanical and hydraulic behavior of rocks in varying temperature conditions, thermo-hydro-mechanical coupling analysis in rock mass and deformation behavior of discontinuous rocks. The mechanical properties were measured with Interaken rock mechanics testing systems and hydraulic properties were measured with transient pulse permeability measuring systems. In all results, rock properties were sensitive to temperature variation.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.257-268
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• 2005

In situ rock mass is generally heterogeneous and discontinuous, with varying degrees of strength along the planes of weakness. The planes of weakness such as joints, faults, cracks and bedding planes, control the strength and deformation characteristics of the rock mass. Subsequently, the stability of underground opening depends upon the spatial distribution of discontinuities and their mechanical properties in relation with geometrical shape of openins as well as the mechanical properties of intact rock materials. Understanding the behaviour of a discontinuous rock mass remains a key issue for improving excavation design in hiかy stressed environments. Although recent advances in rock mechanics have provided guidelines for the design of underground opening in isotropic rock mass, prediction and control of deformation in discontinuous rock masses are still unclear. In this study, parametric study was performed to investigate the plastic zone size, stress distribution and deformation behavior around underground opening in a discontinuous rock mass using a continuum joint model. The solutions were obtained by an elasto-plastic finite difference analysis, employing the Mohr-Coulomb failure criteria. Non-associated flow rule and perfectly plastic material behavior are also assumed.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.573-573
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• 2009

지열에너지는 지구가 생성될 당시부터 지구 내부에 존재하는 무한한 열에너지로 온실가스 배출이 적으며 태양광이나 풍력 등 다른 신재생 에너지와는 달리 일정한 에너지를 공급할 수 있는 항상성 에너지로 기저부하를 담당할 수 있다. 지열을 이용한 전력 생산은 1904년에 이탈리아 라데렐로에서 처음으로 시작되었으며, 현재까지 화산지대를 중심으로 활발히 이루어지고 있다. 2001년에서 2005년 사이에 전세계 지열발전용량은 약 13% 증가하였으며, 2005년을 기준으로 약 8,933MWe의 지열발전설비가 가동 중이다. 최근 들어 지하 심부까지 시추하여 지열저장소(geothermal reservoir)를 형성하고 이를 통해 지열에너지를 생산하는 새로운 시스템인 EGS(Enhanced Geothermal Systems)가 개발됨에 따라 비화산지대에서도 지열발전소를 건설하려는 움직임이 가속화되고 있다. EGS는 지하 심부의 불투수성 결정질 암반에 존재하는 지열에너지의 경제적인 생산뿐만 아니라 물을 주입하여 생산시키는 순환 방식을 이용하여 지열에너지 획득의 매개 역할을 하는 지열수의 고갈 문제를 해결하였다. 결정질 암반에서의 지열저장소의 형성은 암반 내에 분포하는 불연속면에서 주로 발생하며, 이를 위한 압력 조건은 현지 암반의 응력 분포 특성과 암반 및 불연속면의 물성에 좌우된다. 시추공을 통해 지하 심부의 암반에 수압이 가해지면 물의 주입으로 불연속면의 마찰력이 감소하며, 이로 인해 불연속면에 전단변형이 발생하게 된다. 전단변형은 불연속면을 열린 상태로 유지시켜 지열저장소를 형성하게 된다. 불연속면의 전단 변형시 발생하는 미소 탄성파는 시추공 주변에 설치한 모니터링 장비에서 측정되며, 모니터링 장비에 의해 측정된 미소 탄성파 발생 지점의 클러스터는 지열저장소의 공간적 분포 및 규모를 추정할 수 있는 자료가 된다. 현재 EGS를 이용한 지열발전 프로젝트는 프랑스 슐츠, 스위스 바젤, 호주 하바네로에서 대표적으로 진행 중이다. 슐츠는 현재 1.5MWe의 파일럿 플랜트를 가동 중이며, 하바네로는 파일럿 플랜트 건설 단계를 진행중이다. 스위스 바젤은 지열저장소를 형성시킬 목적으로 수행된 주입시험에서 발생된 문제에 대한 기술의 신뢰성을 확보할 목적으로 잠시 중단된 상태다. 제주도는 신생대에 분출하여 형성된 대표적인 한국의 화산지형으로 지열부존 가능성이 높을 것으로 예상되는 지역이다. 따라서 폐사는 지열에너지 부존 특성을 파악하기 위한 심부 물리 탐사 및 탐사정 시추가 실시될 예정이며 궁극적으로 국내 최초의 상용화된 지열발전소 건설을 목표로 하고 있다.

• Tunnel and Underground Space
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• v.27 no.3
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• pp.146-160
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• 2017

$CO_2$ sequestration for alleviating global warming is a hot issue in the world. In this study, TOUGH2 and FLAC3D were combined for analyzing the hyro-mechanical coupling behaviors expected in $CO_2$ sequestration and applied it to Sleipner project carried out in Norway. In the analysis, the influence of pore pressure on in situ stress was considered and the influence of caprock permeability on hydro-mechanical behaviors was analyzed. In the condition of constant injection rate, pressure and saturation at the injection well, liquid and gas saturation in rock, major and minor stress variations with time and distance from the injection well, and horizontal and vertical displacements after injection could be investigated. The major principal stress was quickly increased in the early stage and then slowly decreased to a stable value, which was higher than the initial value. In contrast, the minor principal stress returned to initial value after some increase in the early stage. Surface upheaval was steadily increased and it was up to 15mm in 2 years after injection. When the caprock's permeability was changed from $3e-15m^2{\sim}3e-18m^2$, it was found that the injection well pressure and surface upheaval were inversely propotional to the permeability.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.192-202
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• 2013

The domestic demand of natural gas has increased continuously due to the sudden rise of oil price and regulations on greenhouse gas to global warming. In order to improve the supply security of natural gas market in Korea, the agreement on supply of pipeline natural gas (PNG) in Russia was signed between Gazprom and Korea Gas Corporation in 2008. If the supply plan of Russian natural gas is realized, underground storage facilities would be required in order to balance supply and demand of natural gas because the gas demand is concentrated in the winter. This study investigated the safety of the storage facility in quantitative way considering several design parameters such as gas pressure, depth of the storage cavern, rock condition and in-situ horizontal stress ratio. Two dimensional stress analyses were conducted using axi- symmetry condition to examine the behavior of cavern depending upon suggested design parameters. Results showed that the factor of safety, defined as the ratio of 'shear strength'/'shear stress', was largely affected by the depth, rock class and gas pressure but was insensitive to the coefficient of lateral pressure(Ko).

• Tunnel and Underground Space
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• v.30 no.5
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• pp.473-483
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• 2020

This paper examines the vertical stress change concentrated on mine pillar which occurs due to the stress disturbance from opening excavation at room and pillar mine by FLAC3D, a finite difference method (FDM) software. The mesh size combination is decided with a careful consideration of relative error and run-time, then its performance is verified. A series of numerical analyses is conducted and the vertical stress at central pillar was observed for the test cases of 1×1 to 11×11 mine pillars, 40 m to 320 m depth with 40 m difference. The results show that the vertical stress of pillar approaches to the similar value with the value estimated by tributary area theory(TAT) when the development area (N_P) is increased or the height of overburden (H_OB) is decreased, while it is overestimated in the opposite case. Furthermore, it also represents that the vertical stress factor (VSF) converges to a specific value when the depth is increased whille keeping the development area identical.

• Tunnel and Underground Space
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• v.13 no.5
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• pp.331-343
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• 2003

Though the Grouting has been in use for a long time, it is still regarded as an technique rather than engineering. The study of ground improvement by grouting is rare especially in jointed rock mass. In this study, biaxial compression tests were performed in the jointed rock mass models with .ough surfBce joints assembled with blocks before and after grouting. The load-deformation curves of the jointed rock masses showed a non-linear relationship before grouting but showed a relatively linear deformaion behavior after grouting. Improvement ratio (deformation modulus after grouting/deformation modulus before grouting) decreased with increasing joint spacing and lateral stress. Improvement ratio decreased exponentially with increasing deformation modulus of the rock mass model before grouting. Three-dimensional FDM analysis was performed to a highway tunnel case using experimental data of grouted rock. The convergence of the tunnel predicted after grouting by the numerical modelling coincided with those attained from the field measurement.

• Tunnel and Underground Space
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• v.30 no.6
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• pp.559-572
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• 2020

This paper performs laboratory experiments for borehole stability considering temperature and true triaxial stress condition, and observes a thermo-mechanical behavior of the rock under stress and temperature conditions of deep underground. China yellow sandstone and Hwangdeung granite specimens were used to perform a true triaxial compression test. Mechanical tests were carried out under nine confining pressure conditions, and thermo-mechanical tests using granite samples were carried out under six confining pressure conditions at 60-100℃. In the mechanical tests, maximum principal stress at borehole breakout was proportional to intermediate principal stress. In the thermo-mechanical tests, it was confirmed that thermal stress is added to the stress field of the borehole with the increase in temperature, resulting in additional breakout progress. To analyze the results of the laboratory experiment, Mogi-Coulomb failure criterion was used. The results of traditional triaxial compression test on cylindrical specimens and borehole breakout under true triaxial compressions matched well with Mogi-Coulomb failure criterion.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.185-205
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• 1999

Hydraulic fracturing tests were performed in two inclined boreholes for the design of underground oil storages in Korea. Extensions of their application limits were expected through a precise comparison between the interpretation techniques for the vertical and the inclined boreholes. Especially, it was verified that the magnitude of in-situ stress can be varied even in the same rock mass with a variety of geographic/geotechnical characteristics. It was also demonstrated that its orientation can be changed even in the same borehole with the existence of explicit discontinuities.