• Title/Summary/Keyword: 시추공 레이다 반사법 탐사

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Application of Borehole Radar to Tunnel Detection (시추공 레이다 탐사에 의한 지하 터널 탐지 적용성 연구)

  • Cho, Seong-Jun;Kim, Jung-Ho;Kim, Chang-Ryol;Son, Jeong-Sul;Sung, Nak-Hun
    • 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.

Principles and application of DC resistivity tomography and borehole radar survey. (전기비저항 토모그래피와 시추공 레이다 탐사의 원리 및 응용)

  • Kim Jung-Ho;Yi Myeong-Jong;Cho Seong-Jun;Song Yoon-Ho;Chung Seung-Hwan
    • 한국지구물리탐사학회:학술대회논문집
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    • 1999.08a
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    • pp.92-116
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    • 1999
  • Tomographic approaches to image underground structure using electrical properties, can be divided into DC resistivity, electromagnetic, and radar tomography, based on the operating frequency. DC resistivity and radar tomography methods have been recently applied to site investigation for engineering purpose in Korea. This paper review these two tomography methods, through the case histories acquired in Korea. As another method of borehole radar survey, borehole radar reflection method is included, and its inherent problem and solution are discussed, how to find the azimuth angle of reflector using direction-finding-antenna. Since the velocity anisotropy of radar wave has been commonly encountered in field data, anisotropic radar tomography is discussed in this paper. In DC resistivity tomography, two subjects are focussed, electrode arrays, and borehole effect owing to the conductive fluid in borehole. Using the numerical modeling data, various kinds of electrode ways are compared, and borehole effect is illustrated. Most of the case histories presented in this paper are compared with known geology, core logging data, and/or Televiewer images.

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Application of Radar Survey to a Granite Quarry Mine (화강암 석산 지역에서의 레이다 탐사의 적용)

  • Seol Soon-Jee;Kim Jung-Ho;Cho Seong-Jun;Yi Myeong-Jong;Chung Seung-Hwan
    • Geophysics and Geophysical Exploration
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    • v.4 no.1
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    • pp.8-18
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    • 2001
  • To delineate the inhomogeneities including fractures and to estimate the freshness of rock borehole radar consisting of the reflection and tomography methods, and GPR surveys were conducted at a granite quarry mine. The borehole reflection survey using the direction finding antenna was also conducted to get the spatial orientations of reflectors. 20 MHz was adopted as the central frequency for the borehole radar reflection and tomography surveys and 100 MHz was for GPR. Through the interpretation of borehole reflection data using dipole and direction finding antenna as well as GPR images, which are good agreement with each other, we could determine the orientation of the major fractures in three dimensional way. Parts of travel time curves of tomography data showed the anisotropy, which is uncommon in granite quarry. By comparing the tomography data and TeleViewer images, the anisotropy effect in this area are closely related to fine fissures aligned in the same direction. The area confined by the two fractures, MF2 and MF5, might consist of the most fresh granite in the surveyed area, which was concluded from the borehole radar tomography, and GPR images as well as the distribution of anisotropy.

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Feasibility test on EDZ detection by using borehole radar survey

  • Cho, Seong-Jun;Kim, Jung-Ho;Son, Jeong-Sul;Kim, Chang-Ryol;Sugn, Nak-Hun
    • 한국지구물리탐사학회:학술대회논문집
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    • 2006.06a
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    • pp.239-244
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    • 2006
  • Borehole radar reflection surveys were carried out in the horizontal borehole to detect EDZ while constructing the tunnel for the research facility of the nuclear waste disposal in Korea. The horizontal borehole has been bored at a length of 35 m from shelter to be parallel with the tunnel which would be planed. While the tunnel has been constructing with the explosive excavation, the borehole radar reflection surveys carried out 5 times with the interval of 2 or 4 days for monitoring EDZ. The most typical change of the reflection event resulted from the face of the wall of tunnel which had been produced newly by the excavation of the tunnel daily, EDZ has been detected with constructing images of difference between two measurement stages, and also the change of EDZ through the time has been done, which is due to the generation of crack and weakening of the rock strength of the face of the tunnel's wall near previous portion of the face of a blind end of tunnel according to explosive excavation.

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Automatic Determination of the Azimuth Angle of Reflectors in Borehole Radar Reflection Data Using Direction-finding Antenna (방향탐지 안테나를 이용한 시추공 레이다 반사법 탐사에 있어서 반사층 방위각의 자동 결정)

  • Kim Jung-Ho;Cho Seong-Jun;Yi Myeong-Jong;Chung Seung-Hwan
    • Geophysics and Geophysical Exploration
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    • v.1 no.3
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    • pp.176-182
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    • 1998
  • The borehole radar reflection survey can image the underground structure with high resolution, however, we cannot get any information on the orientation of the reflectors with dipole antenna alone. The direction-finding antenna system is commonly used to give the solution to the problem. However, the interpretation of the data from direction- finding antenna may be time-consuming, and sometimes have ambiguities in the sense of precise determination of the azimuth. To solve the problem, we developed the automatic azimuth finding scheme of reflectors in borehole radar reflection data using direction-finding antenna. The algorithm is based on finding the azimuthal angle possibly showing the maximum reflection amplitude in the least-squared error sense. The developed algorithm was applied to the field data acquired in quarry mine. It was possible to locate nearly all of the reflectors in three dimensional fashion, which coincide with the known geological structures and man-made discontinuities.

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Integrity test and depth estimation of deep foundations (깊은 기초의 건전도시험과 근입깊이 조사)

  • Jo Churl-hyun;Jung Hyun-key;Lee Tai-sup;Kim Hag-soo
    • 한국지구물리탐사학회:학술대회논문집
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    • 1999.08a
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    • pp.202-216
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    • 1999
  • The deep foundation is frequently used for the infrastructures. Since the quality control of the cast-in-place concrete foundations such as CIP piles and slurry walls is not so easy as that of the ready made PC(prestressed concrete) piles, it is necessary to get the information on the integrity of the concrete of the foundation. The depth estimation of foundations whose depths are unknown is also very important in repair and reinforcement works or in safety inspection and assessment to the big structures. The cross-hole sonic logging(CSL) system and the single channel reflection seismic measurement system were developed to test the integrity of pile. The former is well applied to CIP structures, while the later to all kinds of piles with less accurate result compared to that of CSL. To estimate the depth of the deep foundations, parallel seismics, borehole RADAR, and borehole magnetics can be used.

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