• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.4
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• pp.361-371
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• 2009

Resistivity tomography is very effective geophysical method to find out the resistivity distribution and its change in time around a tunnel. Thus, the resistivity tomogram can provide helpful information which is necessary for the effective maintenance of the tunnel. However, an air filled tunnel severely distorts tomography data, especially when the current or potential electrode is placed near the tunnel. Moreover, the distortion can often lead to misinterpretation of tomography monitoring data. To solve these problem, we developed a resistivity modeling and time-lapse inversion program which include a tunnel. In this study, using the developed program we assured that the inversion including a tunnel gives much more accurate image around a tunnel, compared with the conventional tomogram where the tunnel is not included. We also confirmed that the time-lapse inversion of resistivity monitoring data defines well resistivity changed areas around a tunnel in time.

• Geophysics and Geophysical Exploration
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• v.11 no.4
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• pp.368-372
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• 2008

This study evaluates the usefulness and capability of surface electrical resistivity technique for identifying the weak zones or subsurface cavities in karst area with limestone formation. Weak zones or cavities near surface can be potentially dangerous and several problems are associated with collapse of roads or buildings accompanied by subsidence phenomena. In this paper, both two and three dimensional resistivity investigation were conducted to investigate subsidence along a road in Yongweol-ri, Muan-gun, South Korea. The results of the resistivity survey using dipole-dipole array provide a clear view of the weathered regolith, the distribution of weak zones or cavities and bedrock. Several low resistivity areas were identified and subsequent drilling led to the discovery of several weak zone or clay-filled underground cavities. The drilling results show excellent correlation with the resistivity images. It is illustrated, the ability of electrical technique to produce high resolution images of subsurface, which are useful for subsidence assessment. Also the results of this study have demonstrated that two and three dimensional electrical resistivity surveys are useful for delineating the subsidence area. Based on resistivity imaging, the map of hazardous zone has been developed.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.191-201
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• 1999

The interpretation of resistivity data has, so far, mainly been made under the assumption that the earth is of relatively simple structure and then using one or two-dimensional inversion scheme. Since real earth structure and topography are fully three-dimensional and very complicated In nature, however, such assumptions often lead to misinterpretation of the earth structures. In such situations, three-dimensional inversion is probably the only way to get correct image of the earth. In this study, we have developed a three-dimensional inversion code using the finite element solution for the forward problem. The forward modeling algorithm simulates the real field situation with irregular topography. The inverse problem is solved iteratively using the least-squares method with smoothness constraint. Our inversion scheme employs ACB (Active Constraint Balancing) to enhance the resolving power of the inversion. Including Irregular surface topography in the inversion, we can accurately define the earth structures without artifact in the numerical tests. We could get reasonable image of earth structure by Inverting the real field data sets taken over highway bridge construction site.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.1
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• pp.1-8
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• 2015

Recently, constructions of coastal structure including wind turbine structure have increased at southwest shore of Korea. There is a big difference of tide which rage from 3.0 m to 8.0 m at south and wet shore of Korea, respectively. In such ocean circumstance, large scour may occur due to multi-directional tidal current and transverse stress of the wind. therefore scour surrounding wind turbine structure can make system unsafe due to unexpected system vibration. In this study, hydraulic resistance capacity, i.e., critical velocity and critical shear stress, was evaluated by RCT. Uni-directional and bi-directional hydraulic resistance capacities of the samples which were consolidated by different preconsolidation pressures were correlated with soil resistivities of same samples. According to the correlation, it is possible to estimate hydraulic resistance capacity from electrical resistivity of soil. Through the updating the correlation for various soil types, it is expected that the hydraulic resistance capacity of whole construction site will be simply determined from the electrical resistivity.

• Journal of Korean Society of societal Security
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• v.2 no.3
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• pp.39-46
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• 2009

A small loop-loop multi-frequency electromagnetic(EM) induction method is a useful technique to map a resistivity distribution efficiently and non-destructively. However, for quantitative interpretation and depth sounding, the quality of measured data is crucial. In this paper, we propose a bias correction of measured data by using background noise measurements to obtain reliable data, and propose an evaluation technique of apparent that can provide a resistivity image easily. We have performed small loop-loop EM measurements to detect water saturation in a man-made test site. The application of our proposed techniques to the measured data was successful.

• Geophysics and Geophysical Exploration
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• v.8 no.1
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• pp.50-58
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• 2005

Recently, the imaging of geological structures beneath water-covered areas has been in great demand because of numerous tunnel and bridge construction projects on river or lake sites. An electrical resistivity survey can be effective in such a situation because it provides a subsurface image of faults or weak zones beneath the water layer. Even though conventional resistivity surveys in water-covered areas, in which electrodes are installed on the water bottom, do give high-resolution subsurface images, much time and effort is required to install electrodes. Therefore, an easier and more convenient method is sought to find the strike direction of the main zones of weakness, especially for reconnaissance surveys. In this paper, we investigate the applicability of the streamer resistivity survey method, which uses electrodes in a streamer cable towed by ship or boat, for delineating a fault zone. We do this through numerical experiments with models of water-covered areas. We demonstrate that the fault zone can be imaged, not only by installing electrodes on the water bottom, but also by using floating electrodes, when the depth of water is less than twice the electrode spacing. In addition, we compare the signal-to-noise ratio and resolving power of four kinds of electrode arrays that can be adapted to the streamer resistivity method. Following this numerical study, we carried out both conventional and streamer resistivity surveys for the planned tunnel construction site located at the Han River in Seoul, Korea. To obtain high-resolution resistivity images we used the conventional method, and installed electrodes on the water bottom along the planned route of the tunnel beneath the river. Applying a two-dimensional inversion scheme to the measured data, we found three distinctive low-resistivity anomalies, which we interpreted as associated with fault zones. To determine the strike direction of these three fault zones, we used the quick and convenient streamer resistivity.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.185-185
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• 2013

최근 의료 영상 센서는 급속도로 발전을 이룩하여 미세 병변의 위치와 그 크기를 진단하는 데에 많은 이용이 되고 있다. 하지만 기존 flat panel형태의 의료영상 센서는 인체의 굴곡으로 인한 영상 왜곡으로 발전의 한계에 이르고 있는 실정이다. 이 영상 왜곡으로 인한 오진은 환자에게 불필요한 피폭, 수술적 요법, 약물치료 등 환자에게 치명적인 의료사고를 일으킬 수 있다. 이러한 한계를 극복하기 위하여 flexible substrate을 이용한 투명전극들이 의료영상 센서로서의 적용을 연구 되어 졌다. IZO, ITO, FTO 등의 투명전극들 중 Indium Tin Oxide(ITO)는 다른 전극에 비해 높은 투명도와 낮은 저항으로 인하여 다양한 부분에서 널리 이용 되고 있다. 그러나 ITO를 flexible substrate로 적용 시 불충분한 resistivity와 기계적 강도를 지니고 있으며, 유연성을 위해 전극 재료의 두께를 감소시키면 전도성의 문제를 일으키는 단점이 있는 것으로 알려져 있다. 이러한 문제점을 보완 및 해결하기 위하여 본 연구에서는 sputtering magnetron system를 이용하여 polyethylene terephthalate(PET) substrate 위에 ITO을 증착함으로써 전기적 특성을 알아보았다. PET 필름의 크기를 55 절단하였고 증착 온도는 고온에서 수축하는 PET 필름의 물성을 고려하여 $23^{\circ}C$로 설정 하였다. 가스의 분압 비를 Ar는 50ccm으로 고정하고 O2의 비율을 각각 0, 0.2, 0.4, 0.8, 1ccm으로 나눈 후, 비율에 따라 각각 30, 60, 90sec간 sputtering 증착을 하였다. 또한 각각 30, 60, 90sec간 sputtering 증착하여 O2 유량과 sputtering 증착 시간의 변화에 따른 ITO의 전도특성과 유연성에 대한 전도특성을 측정하였다. 유연성을 측정하기 위해선 bending 각도를 각각 $0^{\circ}$ $30^{\circ}$, $45^{\circ}$, $60^{\circ}$로 구부린 후, Two-point probe를 이용하여 변화된 저항을 통해 ITO의 전기적 성질의 변화를 측정 하였다. 측정결과 flexible ITO substrate의 전도특성은 sputtering 증착시간이 증가할수록 저항 값이 낮아지는 것을 확인하였지만, O2 유량이 증가 시 저항이 낮아지다가 다시 증가하는 결과를 알 수 있었다. 본 연구에서는 Ar:O2의 50:0.8의 조건에서 90sec동안 sputtering 증착한 ITO가 131 ${\Omega}/cm^2$의 저항 값이 측정 되었고 다른 조건에서는 164 ${\Omega}/cm^2$에서 4.7 $k{\Omega}/cm^2$까지 저항변화를 가져 Ar:O2의 50:0.8의 조건이 최적화에 좋은 조건이라 판단하였다. 또한 50:0.8의 조건의 ITO의 경우 bending test시에서도 131 ${\Omega}/cm^2$에서 316 ${\Omega}/cm^2$ 정도의 안정적인 저항변화를 가지는 반면 다른 조건에서는 128 ${\Omega}/cm^2$에서 6.63 $k{\Omega}/cm^2$까지의 변화를 나타나 기계적 형상변화에도 분압비가 영향을 주는 것을 확인 할 수 가 있었다. bending 각도에 따른 저항의 변화를 측정하였을 시, 각도 변화에 따라 중심부의 저항 값이 $60^{\circ}$에서 가장 높은 변화가 나타나 전기저항이 높아진 원인을 찾기 위해 Scanning Electron Microscope (SEM)촬영을 한 결과 저항값이 높아짐에 따라 ITO의 압축응력이 작용하는 부근에 Crack이 발생함을 알 수 있었다. 이러한 결과로 flexible ITO substrate의 Crack발생률을 최소화 시키고 bending시 전도성을 유지하기 위해서는 가스의 유량 최적화가 flexible substrate의 기계적형상변화에 대한 ITO의 내구성을 향상시킬 수 있는 해답이 될 것으로 사료된다.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.537-547
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• 2011

Electrical resistivity tomography surveys using boreholes were applied to reveal the cause of a catastrophic land subsidence accompanied by the excessive groundwater withdrawal in urban karst area and to map the connectivity of disseminated cavities over the study area. In order to understand the hydrogeological characteristics, resistivity using exsitu core samples, groundwater level for five boreholes, and hydraulic conductivity using slug test were measured. The hydraulic conductivity variation ranging from 0.8 to $9.3{\times}10^{-4}\;cm/s$ for five boreholes and a gentle slope of groundwater level indicated that there is no significant characteristics of hydraulic heterogeneity. Core samples of the lime-silicated rock were classified as three groups including cracked, weathered, and fresh and measured the resistivity values ranged from 103 to 161, 218 to 277, and 597 to 662 ohm-m, respectively. Drilling results that showed the cavity filled with clay materials and tomogram for this region indicated resistivity value lower than 50 ohm-m. From the inverted resistivity results for each section with five boreholes, cavity and fractured layer were distributed along the depth between 10 and 20 m overall area and cavities ranging from 4 to 6 m filled with clay materials.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.93-98
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• 2009

Comprehension of physical properties distribution of underground cavity must be made primarily to show the clear image of the state of the cavity. A physical scale model experiment is executed assuming that underground cavity in filled with air or water of different ratio. The state of cavity wall is considered wet. Cavity model is made of agar. As a experimental result, even if the cavity wall is wet, high air and water ratio cavity shows high anomaly.

• The Journal of Engineering Geology
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• v.15 no.1
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• pp.19-27
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• 2005

The Sambo mine is located in Hae-je Myeon, Moo-an Gun, Chollanamdo, which consists of host gneiss and rhyolite possessing quartzite veins with other compositions such as gold, silver, and sublimated sulfur. The ore grade estimated from the core was 0.05～10.9g/t or less in gold and 0.05～389g/t or less in silver, indicating a partial mineralization. The purpose of this paper is to understand the subsurface structures and the distribution of mineralized bodies in the Sambo mine using a combined method of Schlumberger, Wenner, and Dipole-di-pole resistivity surveys on the surface and the resistivity tomography survey in boreholes. The result of three-dimensional resistivity inversion showed that the mineralized body is extended to 240m long in the N10°～20°E direction, with 30m wide and 80 m thick from the surface. The low resistivity zones (<1,000ohm-m) determined from the resistivity image were in good agreement with the mineralized bodies and weak zones identified from the logged cores.