• Geophysics and Geophysical Exploration
• /
• v.18 no.4
• /
• pp.223-231
• /
• 2015

Self-potential (SP) is sensitive to groundwater flow and there are many causes to generate SP. Among many mechanisms of SP, pore-fluid flow in porous media can generate potential without any external current source, which is referred to as electrokinetic potential or streaming potential. When calculating SP responses on the surface due to geothermal fluid within an engineered geothermal system (EGS) reservoir, SP anomaly is usually considered to be generated by fluid injection or production within the reservoir. However, SP anomaly can also result from geothermal water fluid within EGS reservoirs experiencing temperature changes between injection and production wells. For more precise simulation of SP responses, we developed an algorithm being able to take account of SP anomalies produced by not only water injection and production but also the fluid of geothermal water, based on three-dimensional finite-element-method employing tetrahedron elements; the developed algorithm can simulate electrical potential responses by both point source and volume source. After verifying the developed algorithm, we assumed a simple geothermal reservoir model and analyzed SP responses caused by geothermal water injection and production. We are going to further analyze SP responses for geothermal water in the presence of water production and injection, considering temperature distribution and geothermal water flow in the following research.

• Economic and Environmental Geology
• /
• v.16 no.1
• /
• pp.11-18
• /
• 1983

Gyeongsang Basin in the southeastern part of the Korean peninsular is characterized by many fault systems. To decipher the geotectonical evolution of the Korean peninsular and marginal basins in her adjacent areas it is prerequisite to understand the spatial distribution pattern and mutual relationships of these fault systems. Because of difficulties in finding any criterion to recognize the faults in field, their extension and mutual relationships in ages are not very clear yet. As an attempt to find geophysical criteria to recognize the fault, geoelectrical resistivity survey was carried out in this study. With the Wenner configuration four resistivity soundings and twenty seven resistivity profilings were done. The electrode distance used was up to 50m. From the results of the resistivity soundings and boring data of earlier groundwater investigations the depth of alluvial and weathered zone was established to be at most 20m in the study area. In the resistivity profiling low resistivity anomaly zones are detected on every traverse, which are interpreted as caused by fractures, fault clays and mylonites in the fault zone. The width of the fault zone amounts to 0.3-1km. By correlating and connecting the negative anomaly zones from traverse to traverse one can determine the trend of th of the faultzone and therefore that of fault itself. The recognized fault trend in this way was $N15^{\circ}-20^{\circ}E$ and this coincides with the direction of the inferred fault line from earlier geological surface mapping. With the help of this characteristical negative anomaly the existance of another $N80^{\circ}W$ trending fault was estabished. This study has shown that geoelectrical resistivity survey can be applied successfully to the problem of tracing fault line insofar as a fault zone has been developed along fault line.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.8
• /
• pp.15-27
• /
• 2004

Sliding aspects of rock slope, where large-scaled tension cracks are induced during preliminary excavation, have been analyzed. Structure of rock mass is investigated by performing the electrical resistivity survey and the orientations and positions of discontinuities are measured from DOM-drilled core log. Geological evidence far primary failure movement has been detected and clay minerals which possess swelling properties are identified through XRD analysis. Slope stability is examined by considering the orientations of discontinuities and their trace distributions on the cut-face and neighboring natural slope surface. Both orientations and positions of failure-invoking discontinuity planes, traces of which are exposed within the anticipated sliding region, are concerned fur analyzing the preferred sliding directions. Regional sliding vectors are assessed based on the relative positions of potential sliding planes in the boreholes and the general trend of anticipated failure movement of rock slope is also investigated.

• Tunnel and Underground Space
• /
• v.17 no.1 s.66
• /
• pp.66-74
• /
• 2007

The analysis of ground subsidence stability was conducted for the residential area located on the limestone corrosion zone. For the investigation of the cavity distribution in limestone region, various geophysical investigations such as electroresistivity tomography, electromagnetic prospecting are carried out. Geotechnical field tests with drilling are also carried out for the evaluation of the ground characteristics. Based upon their results, numerical modeling is performed for the simulation and prediction of the ground subsidence with the conditions of cavity geometry and groundwater level. The main factor to cause the ground subsidence is estimated as the draw down of the groundwater level below soil overburden, which disturbs the mechanical equilibrium of ground and drives washing away the overburden soil through the cavity and solace subsidence. It seemed that it is essential to maintain the groundwater level continuously above the shallow cavity for the prevention of the ground subsidence on the limestone corrosion zone.

• The Journal of the Convergence on Culture Technology
• /
• v.6 no.2
• /
• pp.467-472
• /
• 2020

Methods for deriving design input-parameters to ensure the stability of a structure on a common ground are generally well known. Folded metamorphic rocks, such as the study area, are highly foliated and have small faults parallel to the foliation, resulting in special research methods and tests to derive design input parameters, Etc. are required. The metamorphic rock ground with foliation development of several mm intervals has a direct shear test on the foliation surface, the strike/dip mapping of the foliation, the boring investigation to determine the continuity of the foliation, and the rock mass rating of the metamorphic rock. etc. are required. In the case of a large number of small foliation-parallel faults developed along a specific foliation plane, it is essential to analyze the lineament, surface geologic mapping for fault tracing, and direct shear test. Folded ground requires additional geological-structural-domain analysis, discontinuity analysis of stereonet, electrical resistivity exploration along the fold axis, and so on.

• Proceedings of the Korean Quaternary Association Conference
• /
• 2004.06a
• /
• pp.46-46
• /
• 2004

Van Mijenfjorden은 스발바드 군도의 Spitsbergen 서부에 위치하는 두 번째로 큰 피오르드로 온난하고 염분도가 높은 북대서양의 표층수가 북극해로 유입되는 Gateway에 위치하기 때문에 전지구적이며 지역적인 기후변화의 영향을 받는 지역이다. 1999년 IMAGES 프로그램의 일환으로 프랑스 탐사선인 'R/V Marion Dufresne'을 이용하여 북극해의 스발바드 군도에 위치하는 Van Mijenfjorden (77$^{\circ}$ 46.87'N and 15$^{\circ}$ 17.81'E)에서 약 18m의 빙ㆍ해양 퇴적물 코아(MD99-2305)를 시추하여 마지막 최대 빙하기 이후의 고환경변화를 연구하였다. AMS 14C 연대 측정에 의하면 diamicton 층인 하부 2m를 제외한 16m의 퇴적층은 지난 12cal. ka BP경에 피오르드에 존재하던 조수빙하(tidewater glacier)가 해빙되기 시작한 이후에 퇴적되었다. 특히 유기지화학 자료와 부유성과 저서성 유공충의 산출양상 그리고 저서성 유공충인 C. reniforme의 산소ㆍ탄소 안정동위원소 비에 의하면 코아 MD99-2305에는 Van Mijenfjorden에서 홀로세 동안에 일어난 퇴적환경변화를 잘 기록하고 있다. 특히 홀로세 동안에 피오르드내의 퇴적환경 변화는 조수빙하의 확장과 후퇴와 밀접한 관계가 있으며, 유기물의 탄소동위원소(13Corg) 비는 -24에서 -22$\textperthousand$ 값의 변화를 보인다. 이는 Van Mijenfjorden 퇴적물에 공급된 유기물은 육상과 해양기원이 혼합되어 퇴적되었음을 지시한다. 지난 12 cal. ka BP 이후 13Corg 값이 뚜렷하게 변하는 것은 Van Mijenfiorden에서 조수빙하의 변동과 표층수에서의 생산력의 변화를 강하게 반영한다. 강하게 반영한다.53%가 이공계 출신, 100대 기업 CEO의 38.4%가 이공계 출신, 대입수능시험에서 자연계 지원비율이 감소 -40.1%('99)\$\longrightarrow$34.7%('00)\$\longrightarrow$29.4%('01)\$\longrightarrow$26.9%('02)\$\longrightarrow$30.3%('03)\$\longrightarrow$31.5%\$\longrightarrow$'04)필요성, 효과적인 운전자 교육 정책 등이 그것이다. 자동차 긴급 피난 차선은 유용한 시설로 여러곳에서 그 기능이 발휘되고 있으므로 많은 고속도로 관계자들은 설계, 시공 및 유지 관리 측면에서 유의해야 할 것이다.미세조직을 광학현미경으로 압출방향에 평행한 방향과 수직방향으로 관찰하였고, 열간 압출재 이방성을 검토하기 위하여 X선 회절분석을 실실하여 결정방위를 확인하였다. 전기 비저항 및 Seebeck 계수 측정을 위하여 각각 2$\times$2$\times$10$mm^3$ 그리고 5$\times$5$\times$10TEX>$mm^3$ 크기의 시편을 준비하였다.준비하였다.전류를 구성하는 주요 입자의 에너지 영역(75~l13keV)에서 가장 높은(0.80) 상관계수를 기록했다. 넷째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의 발달과 밀접한 관계가 있음을 시사한다.se that were all low in two aspects, named "the Nonsignificant group". And the issues were

• Journal of the Korean Geosynthetics Society
• /
• v.14 no.2
• /
• pp.95-103
• /
• 2015

In this study, the causes and countermeasures for the leakage of a sea dyke under construction are analyzed. In general, the seabed ground is clearly divided from the embankment but a lot of parts show abnormal zones with low resistivity from the results of electric resistivity survey. Hence the causes of the leakage are considered as following: three-dimensional shear strain behavior, irregular compulsory replacement of the soft seabed ground with low strength and quality deterioration of the waterproof sheets during the closing process. The improvement method is determined by considering the constructability in the seawater and its velocity condition, durability, economic feasibility, similar application cases and so on. Consequently, a combination of low slump mortar and slurry grouting and injection method is selected as an optimum combination. Mixing ratio and improvement pattern are determined after drilling investigation and pilot test. The improvement boundary is separated into general and intense leakage area. The construction is performed with each pattern and the improvement effects are confirmed. The confirmed effects with various tests after completion show tolerable ranges for all of the established standards. Finally, various issues such as prediction of length of the waterproof sheet, installation of it against seawater velocity, etc. should be considered when sea dykes are designed or executed around the western sea which has high tide difference.

• Journal of Environmental Impact Assessment
• /
• v.25 no.3
• /
• pp.209-221
• /
• 2016

The section from water source to 2.6km upper stream of Hantan River is protected as the drinking water quality protection area according to guidelines of Ministry of Environment, because water source of the Gwanin water intake plant has been known the river. However, opinions were consistently brought up that the standard of water source protection zone must be changed with using underground water as water source because of contribution possibility of underground water as the water source of Gwanin water intake facility. In this regard, hydrogeologic investigation including resistivity survey and hydrogeochemical investigation were carried out to assess water source and infiltration of contaminant for the plant. Quaternary basaltic rocks (50m thick with four layers) covered most of the study area on the granite basement. As the result of the resistivity survey, it is revealed that permeable aquifer is distributed in the boundary of two layers: the basaltic layer with low resistivity; and the granite with high resistivity. Considering of outflow from Gwanin water intake facility, the area possessing underground water was estimated at least $5.7km^2$. The underground water recharged from Cheorwon plain was presumed to outflow along the surface of unconformity plane of basalt and granite. Based on field parameters and major dissolved constituents, groundwater and river water clearly distinguished and the spring water was similar to groundwater from the basaltic aquifer. Temporal variation of $SiO_2$, Mg, $NO_3$, and $SO_4$ concentrations indicated that spring water and nearby groundwater were originated from the basaltic aquifer and other groundwater from granitic aquifer. In conclusion, the spring of the Gwanin water intake plant was distinguished from river water in terms of hydrogeochemical characteristics and mainly contributed from the basaltic aquifer.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.18 no.1
• /
• pp.1-12
• /
• 2016

When utilizing a Tunnel Boring Machine (TBM) for tunnelling work, unexpected ground conditions can be encountered that are not predicted in the design stage. These include fractured zones or mixed ground conditions that are likely to reduce the stability of TBM excavation, and result in considerable economic losses such as construction delays or increases in costs. Minimizing these potential risks during tunnel construction is therefore a crucial issue in any mechanized tunneling project. This paper proposed the potential risk events that may occur due to risky ground conditions. A resistivity survey is utilized to predict the risky ground conditions ahead of the tunnel face during construction. The potential risk events are then evaluated based on their occurrence probability and impact. A TBM risk management system that can suggest proper solution methods (measures) for potential risk events is also developed. Multi-Criterion Decision Making (MCDM) is utilized to determine the optimal solution method (optimal measure) to handle risk events. Lastly, an actual construction site, at which there was a risk event during Earth Pressure-Balance (EPB) Shield TBM construction, is analyzed to verify the efficacy of the proposed system.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.6
• /
• pp.17-29
• /
• 2009

There has been an increase in the investigation of deep sea sediments with a consequent increase in the amount of energy required to undertake these investigations. The geotechnical characteristics of Ulleung Basin sediment are explored by using depressurized specimens following methane production tests carried out on pressured core samples obtained at 2,100 m water depth and 110 m below sea floor. Geotechnical index tests, X-ray diffraction, and scanning electron microscope are conducted to identify the geotechnical index parameters, clay mineralogy, chemical composition, and microstructure of the sediments. Compressibility, and elastic and electromagnetic wave parameters are investigated for two samples by using a multi sensing instrumented oedometer cell. The strength chatracteristics are obtained by the direct shear tests. The dominant clay minerals are mostly kaolinite, illite, chlorite, and calcite. The SEM shows a well-developed flocculated structure of the microfossil. Void ratio, electrical resistivity, real permittivity, conductivity, and shear wave velocity show bi-linear behavior with the effective vertical stress: as the vertical effective stress increases. The friction angle obtained by the direct shear test is about $21^{\circ}$, which is similar to the value observed in the Ulleung Basin sediments. This study shows that the understanding of the behavior acting on the diatomaceous marine sediment is important because it often maintains the useful energy resources such as gas hydrate and so will be the new engineering field in the next generation.