• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.369-376
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• 2007

Electrical resistivity tomography was carried out at seawater intrusion monitoring wells located at watershed in coastal areas. It is difficult to identify the characteristics of resistivity near monitoring well in case of using high signalto-noise ratio array due to the high conductivity condition in coastal aquifer although electrical resistivity survey is well adopted to delineate hydrogeological characteristics with the distribution of electrical resistivity. To improve the quality of electrical resistivity survey for two sites with seawater intrusion monitoring wells, inversion with the results of holeto-surface electrical resistivity tomography using single well was executed. The results of inversion for aquifer near wells were verified with the results of drilling log with the informations of fracture, electrical conductivity logging and normal resistivity logging. The inversion for aquifer near one of two wells was also performed at low and high tide with the same electrodes, respectively. From the inversion result, it is possible to obtain the resistivity images with high resolution and to identify the characteristics of aquifer related to seawater intrusion with tidal fluctuation. From this study, it was demonstrated that the hole-to-surface electrical resistivity tomography method accompanied with drilling log, electrical conductivity logging and normal resistivity logging would be useful to delineate the hydrogeological structures near monitoring wells in coastal areas.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.354-357
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• 2004

방사성폐기물 처분 연구의 일환으로 대전 유성북부 화강암 지역내 200～500m 심도를 갖는 9개의 심부 시추공이 착정되었으며, 이중 3개 시추공에 대하여 다중패커시스템이 설치되어 장기적으로 심도별지하수의 수리특성, 화학특성 및 동위원소 특성이 모니터링 되고 있다. 다중패커시스템이 설치되기 전의시추공 지하수의 수리 및 지화학 특성은 심도에 따라 별다른 특성이 보이지 않지만, 다중패커시스템 설치 후, 심도에 따라 특징적인 수리 및 지화학특성을 보여주고 있다. 또한, 다중패커시스템이 설치된 시추공의 경우, 최상부 구간을 제외하고 모든 구간 지하수의 수리화학특성은 일정기간이 경과한 후에는 각 구간별로 거의 일정한 값으로 유지되고 있음을 보여준다. 그러나, 지하수의 함양특성이 크게 변하는 우기 동안에는 지하수 수두압이 심도 약350m의 구간까지 변화되는 특성을 보여주고 있다. 동위원소특성 역시 심도구간에 따라 특징적인 값을 보여주며, 장기적으로 일정한 구간별 특정 값을 보여주고 있다.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.561-573
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• 2023

Korea Atomic Energy Research Institute (KAERI) constructed the KURT (KAERI Underground Research Tunnel) to analyze the hydrogeological/geochemical characteristics of deep rock mass. Numerous boreholes have been drilled to conduct various field tests. The selection of suitable investigation intervals within a borehole is of great importance. When objectives are centered around hydraulic flow and groundwater sampling, intervals with sufficient groundwater flow are the most suitable. This study defines such points as hydraulic outliers and aimed to detect them using borehole geophysical logging data (temperature and EC) from a 1 km depth borehole. For systematic and efficient outlier detection, machine learning algorithms, such as DBSCAN, OCSVM, kNN, and isolation forest, were applied and their applicability was assessed. Following data preprocessing and algorithm optimization, the four algorithms detected 55, 12, 52, and 68 outliers, respectively. Though this study confirms applicability of the machine learning algorithms, it is suggested that further verification and supplements are desirable since the input data were relatively limited.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.4
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• pp.491-505
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• 2018

As an alternative to deep geological disposal technology, which is considered as a reference concept, the domestic applicability of deep borehole disposal technology for high level radioactive waste, including spent fuel, has been preliminarily evaluated. Usually, the environment of deep borehole disposal, at a depth of 3 to 5 km, has more stable geological and geo-hydrological conditions. For this purpose, the characteristics of rock distribution in the domestic area were analyzed and drilling and investigation technologies for deep boreholes with large diameter were evaluated. Based on the results of these analyses, design criteria and requirements for the deep borehole disposal system were reviewed, and preliminary reference concept for a deep borehole disposal system, including disposal container and sealing system meeting the criteria and requirements, was developed. Subsequently, various performance assessments, including thermal stability analysis of the system and simulation of the disposal process, were performed in a 3D graphic disposal environment. With these analysis results, the preliminary evaluation of the domestic applicability of the deep borehole disposal system was performed from various points of view. In summary, due to disposal depth and simplicity, the deep borehole disposal system should bring many safety and economic benefits. However, to reduce uncertainty and to obtain the assent of the regulatory authority, an in-situ demonstration of this technology should be carried out. The current results can be used as input to establish a national high-level radioactive waste management policy. In addition, they may be provided as basic information necessary for stakeholders interested in deep borehole disposal technology.

• The Journal of Engineering Geology
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• v.15 no.1
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• pp.1-8
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• 2005

As a trial to find an efficient technique for determining hydraulic conductivity, a test application of electrical conductivity measurement technique was made using a signal conditioning data acquisition system in borehole. The experiment was made in two test boreholes BM-2 and BM-3 which are located in the Experiment forests of Kangwon National University in Bongmyongri, Chunchon. We obtained series of electric conductivity variation curves after the beginning and completion of saline water injection using these two bore-holes as the pumping well and the observing well alternatively, The analysis of time series electrical conductivity data suggests kinds of valuable information about aquifer properties by holes and depths, and we could confirm the potential of this method as an efficient tool for in situ aquifer test.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.258-262
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• 2003

연안지역에서 해수침투대의 평가를 위하여 다양한 물리검층을 수행하였다. 특히, 해수침투대의 정량적인 평가에 활용될 수 있는 지층의 공극측정은 매우 어려운 문제중의 하나이다. 연안지역의 경우, 미고결지층에 대한 불교란 시료 채취가 어렵고 대부분의 관측정은 시추공 붕락방지를 위하여 내경 50mm 의 PVC 케이싱을 설치하는 경우가 많기 때문에 공극의 측정은 현실적으로 많은 어려움이 따른다. 본 연구에서는 전남 영광지역에서 각종 조사목적으로 굴착한 시추공에서 다양한 물리검층을 수행하여 공내수의 높은 전기전도도가 기원하는 지층을 확인하고자 하였다. 전자유도검층과 공극검층을 수행한 시추공(YK-4호공)에 대한 해석결과, 공내수의 높은 전기전도도는 물리검층법으로 추정한 사질층 공극수와 비슷한 범위를 보였다. 물리검층법으로 추정한 공극이나 높은 염수를 보이는 구간에 대한 해석결과는 보완해야할 많은 부분이 있지만 제한된 현장 상황에서 조사결과의 불화실성을 줄이는데 많은 기여를 할 것으로 기대된다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.528-531
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• 2003

안산시 단원구 대부동, 보령시 청소면 장곡리와 서천군 비인면 선도리의 해안가 4곳에서 전기비저항 탐사를 이용하여 해수침투 조사용 관측정 주변의 대수층구조와 해수침투여부를 파악하고자 하였다. 공내수의 심도별 전기전도도를 확인 해본 결과, 4개의 조사공에서 180-48,000$\mu$S/cm의 각기 다른 값을 보였으며, 전기비저항 검층의 결과에서는 16인치 Short-Normal 검층 0.5-19.28$\Omega$m, 64인치 Long-Normal 검층 1.36-47.45$\Omega$m 그리고 Lateral 검층에서는 0.16-6.69$\Omega$m의 값의 분포를 보였다. 이를 통해 해수에 의해 지하수 및 주변 지질이 완전히 오염된 관측정과 우려되거나 아직 해수침투가 일어나지 않은 관측정을 구분할 수가 있었다. 또한 시추공-지표간 토모그래피를 통해 관측정 주변의 개략적인 수리지질 구조도 파악할 수 있었다.

• Geophysics and Geophysical Exploration
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• v.9 no.4
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• pp.279-290
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• 2006

The borehole radar methods used to tunnel detection are mainly classified into borehole radar reflection, directional antenna, crosshole scanning, and radar tomography methods. In this study, we have investigated the feasibility and limitation of each method to tunnel detection through case studies. In the borehole radar reflection data, there were much more clear diffraction signals of the upper wings than lower wings of the hyperbolas reflected from the tunnel, and their upper and lower wings were spreaded out to more than 10m higher and lower traces from the peaks of the hyperbolas. As the ratio of borehole diameter to antenna length increases, the ringing gets stronger on the data due to the increase in the impedance mismatching between antennas and water in the boreholes. It is also found that the reflection signals from the tunnel could be enhanced using the optimal offset distance between transmitter and receiver antennas. Nevertheless, the borehole radar reflection data could not provide directional information of the reflectors in the subsurface. Direction finding antenna system had a advantage to take a three dimensional location of a tunnel with only one borehole survey even though the cost is still very high and it required very high expertise. The data from crosshole scanning could be a good indicator for tunnel detection and it could give more reliable result when the borehole radar reflection survey is carried out together. The images of the subsurface also can be reconstructed using travel time tomography which could provide the physical property of the medium and would be effective for imaging the underground structure such as tunnels. Based on the results described above, we suggest a cost-effective field procedure for detection of a tunnel using borehole radar techniques; borehole radar reflection survey using dipole antenna can firstly be applied to pick up anomalous regions within the borehole, and crosshole scanning or reflection survey using directional antenna can then be applied only to the anomalous regions to detect the tunnel.

• Tunnel and Underground Space
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• v.15 no.1 s.54
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• pp.28-38
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• 2005

According to the recent development of measurement system utilizing one or a set of boreholes, visualization of the explored underground became to be a major issue. It induced even the introduction of monitoring apparatuses on the borehole wall with multi-function tool, but the usage of these was often limited by where is unfavorable rock condition and a few of engineers can approach. And so, a portable type of borehole camera with only the essential function has been investigated and a few of commercial models about this is recently being applied into the field condition. This paper was based on the monitoring results obtained using a commercial model by Dr. Nakagawa. Discontinuities in rock mass were the topic for the visualization, and it was studied how can visualize their three dimensional distribution and what a numerical formulation is needed and how to understand the visualization result. The numerical formulation was based on the geometric correlation between the dip direction / dip of discontinuous plane and the trend / plunge of borehole, a set of the equation of a plane was induced. As field application of this into two places, it is found that the above visualization methodology will be especially an useful geotechlical tool for analyzing the local distribution of discontinuities.

• Journal of the Korean Geophysical Society
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• v.9 no.1
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• pp.37-45
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• 2006

Velocity structures were defined in the vicinty of the 140-m deep test borehole in the pungam basin through simultaneous inversion of surface seismic refraction and far-ofset VSP traveltime data. Seismicenergy generated at the surface by a seisgun was recorded both at 42 surface locations at 3-m intervalsalong the profiles in the N20E and its orthogonal directions and at 71 m depth in the borehole. Forthe ofset VSP study, seismic energy was generated by a 5 kg sledgehamer at the surface in the horizontal ofset range of -19.5∼+19.5 m from the borehole. The seismic signals were detected at 9∼99 m depths with 1∼2 m intervals and recorded for 204 ms per shot. After shot static corrections,first-arrival times picked from both the surface refraction and borehole records were simultaneouslyinverted to yield velocity tomograms. The tomograms indicate that a 1.5 m thick soil layer with velocities les than 500 m/s overlies basements having a velocity range of 3,067 ∼5,717 m/s. Within the basements,∼4 m and deeper than 71 m. The high-velocit yzones may be due to conglomerates intercalated with sandstones and siltstones. No evidence for large-scale fracture zones or faults is detected near the borehole