• 한국지구물리탐사학회:학술대회논문집
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• 2002.09a
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• pp.46-66
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• 2002

High-resolution multichannel seismic data were collected in the coastal area near the Gori nuclear power plant to investigate Quaternary fault pattern and timing. A 12 channel streamer, a sparker, and a portable recorder were used for data acquisition. Because the group interval of the streamer was 6.25 m and the sparker can generate acoustic waves with the frequency content of up to 500 Hz, the data show a significant improvement both in horizontal and vertical resolution. The area surveyed is covered with 30-40 m thick Holocene sediments that constitute the mud belt along the southeastern coast of Korea. The survey area is characterized by the well discriminated Pleistocene and Holocene boundary and shallow gas-charged zones. A number of Quaternary faults were found in the sediment column, that are nearly vertical and extend north-south. The Quaternary faults, arranged at a spacing of a few hundred meters, suggest that they were formed in response to compression, although some of them reveal extensional characteristics. Locally, faults disrupt Incised-channel fills that are interpreted to have formed in the early stage of transgression after the beginning of the Holocene. Seismic sections suggest that shallow gas in the mud belt sediments made its way upward through the fractured fault planes. The tectonism responsible for the opening of the East Sea has not persisted since the late Miocene, but vigorous Quaternary faulting activity in the vicinity of the southeastern Korean Peninsula indicates that tectonic stability has yet to be achieved in this region underlain by the hotter than normal mantle.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.793-798
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• 1999

This study was conducted to evaluate structural integrity and crack source location of plain concrete beams using acoustic emission. Three point bending tests were carried out plain concrete specimen under cyclic loadings. The variable is W/C of concrete. From the tests it was shown that a breakdown of the kaiser effect and high AE activities during unloading could be effective indices to estimate the level of deterioration in plain concrete structures. The time and location and propagation of crack could be easily determined by monitoring AE, which concludes that AE technique can be a very useful tool to evaluate structural integrity of concrete plain beams.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.896-902
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• 2000

Crack detection technique for concrete structures has been developed in this study,. The technique utilizes OTDR(Optical Time Domain Reflectometer) method that is widely used in the field of optical engineering. At present, some techniques, such as the naked eye inspection, inspection by crack gauge, ultra sonic detection and os on, are used for crack detection. However, these are not economical and are often time-consuming works. This method employs a common optical fiber as a means of crack detection. Th optical fiber is fully attached to concrete surface, and a crack on concrete could be detected to synchronize with the crack on optical fiber. The experimental verification was performed for concrete beams and the intial crack on the beam was detected under cracking force.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.423-428
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• 2000

This Study was conducted to evaluate structural integrity and crack source location of RC structures strengthened with Carbon Fiber Reinforced Plates using acoustic, Four pont bending tests were carried out RC reinforced with C.F.R.P for the several strengthening specimens, the process of fracture was monitored by Acoustic Emission and duration and energy in AE parameters were analyzed. The location and propagation of crack could be easily determined by monitoring AE, which concluded that AE technique could be a very useful tool to evaluate structural integrity of reinforced RC structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.181-188
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• 2002

The objective of this study is to determine crack depth located under steel reinforcement in concrete specimens using ultrasonic method. Experimental studies were performed on concrete specimens containing vertical and inclined surface-opening cracks with known depths. The other studies were carried out on specimens with flexural crack. Experimental results have shown that the crack depth is effectually measured when the distance between the probes is less than the crack depth. The effect of steel on crack depth estimation is studied through a model by considering P-waves diffaction at the tip of crack and steel. In addition, experimental results show that the ultrasonic method is one of useful methods to evaluate the crack depth in reinforced concrete.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.307-314
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• 2010

Although conventional seismic data processing is based on the assumption that the media are isotropic, the subsurface is often anisotropy in shale formation or carbonate with cracks and fractures. This paper presents the anisotropic parameter and seismic modeling in transversely isotropic media with a vertical symmetry axis using seismic physical modeling. The experiment was successfully carried out with VTI media, laminated bakelite material, using contact transducer of p and s-wave transmission. The variation of velocities with angle of incidence was clearly shown in anisotropic material. Comparing these velocities with the calculated phase velocities, the (P) and (S)-wave velocity observed in anisotropic material was a very good agreement with the calculated values. Anisotropic parameter ${\varepsilon}$, ${\delta}$, ${\gamma}$ was estimated by using Lame's constant calculated from the observed velocity. For the purpose of testing (S)-wave polarization, a birefringence experiment was carried out. The higher velocity was associated with the polarization parallel to the fracture, and the lower velocity was associated with the polarization perpendicular to the fracture.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.717-733
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• 2019

In this study, lining thickness distribution and its behind state (particularly, its void state) were analyzed using the GPR survey data performed on three currently operating NATM tunnels. Results of GPR analysis showed that void areas were mostly detected between concrete lining and primary support, particularly, near the crown of the tunnels. The lining thickness in the left-hand side of the tunnel was different from that of the right-hand side by 8.6~253.5 mm when measured in transverse direction. It was also found that longitudinal cracks were prevailed in the area lining thickness was sharply changed. Longitudinal thickness distribution at the crown was also studied and tested by performing 3 goodness-of-fit tests in order to find the most suitable thickness distribution. Normal distribution (or similar distribution) fit most suitably to the measured data if the measured average thickness was larger than designed one; Gamma and/or Inverse Gauss distribution fit to the measured data reasonably well if the measured average thickness was less than the designed value of thickness. Since actual lining thickness can be a potential index when assessing the state and safety of the unreinforced NATM tunnel lining, measuring of the lining thickness with GPR survey might be needed rather than assuming the thickness is always constant and same with the designed value.

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

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.354-354
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• 2015

코팅 층과 소지 사이의 접합력 평가를 위하여 박리 시험법(Peel Off Test), 블리스터 시험법(Blister Test), 압입균열 시험법(Indentation Test), 직접 인장 시험법(Direct Full Off Test), 스카치 테이프 시험법(Scotch Tape Test), 그리고 스크래치 시험법(Scratch Test) 등이 사용되어 왔다. 이 중 박리 시험법과 스카치 테이프 시험법이 산업계에서 일반적으로 사용되고 있다. 전자 산업계에서 많이 사용되고 있는 박리시험법은 금속박막과 절연체 기판 사이의 접합력을 간단하게 측정할 수 있으며, 실험값의 재현성이 뛰어난 장점이 있다. 또한, 측정하는 동안 만들어지는 박리 곡선(Peel Curve)로부터 분석의 신뢰성 여부를 확인할 수 있다. 이러한 장점에도 불구하고 박리 시험법 특성 상 금속 코팅층의 강도가 금속 피막/기판간 접합 강도를 초과하여야 하기 때문에 수백 nm 이하의 박막의 접합력 측정에는 적용하기가 어렵다. 이에 반하여, 스카치 테이프 분석법은 일정길이의 접착 테이프를 박막 표면에 붙인 후 다시 떼어내면서 접착력을 평가하는 방법으로, 박막의 접합력 평가에 적용이 가능하다. 그러나 이 방법은 합격 불합격 여부를 판정하는 정성적인 방법으로 정량평가가 어렵다. 또한, 박막에 접착 테이프를 붙일때의 압력, 테이프를 박리할 때의 각도 및 속도를 일정하게 제어하기가 쉽지 않아 결과의 신뢰성이 높지 않다. 스크래치 테스트는 탐사침(Stylus)을 이용하여 박막의 표면에 하중을 증가시키면서 기판을 이동하여, 피막의 균열이나 박리될 때의 임계 하중값 (Critical Load; Lc)을 측정하는 방법이다. 이 방법은 시편 준비가 쉽고 간단하여 빠른 분석이 가능하고, 수백 nm 이하의 박막에도 적용 가능하다. 또한, 접합력을 정량화 할 수 있기 때문에 변수에 따른 접합력 비교가 용이하다는 장점이 있다. 이와 같은 분석적 장점에도 불구하고, 스크래치 시험을 통한 접합력 측정 방법은 아직까진 산업적으로 널리 활용되지 못하고 있다. 따라서, 본 연구에서는 스크래치 테스트의 원리 및 이론에 대하여 간략히 알아보고, 스크래치 분석을 이용한 접합력 비교에 대한 실제 사례들을 소개하고자 하였다.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.65-70
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• 2005

A low resistivity zone is found in many places such as a fractured fault zone, weathered zone and aquifer. The electrical resistivity is influenced mainly by pore fluid as well as the clay mineral types and contents, Hence, it is very important to understand the relationship between the electrical resistivity and clay contents associated with the low resistivity zone for geotechnical applications such as civil engineering. This study examines the characteristics of clay mineral types and contents to electrical resistivity through sample measurements, and proposes an expression relating the resistivity and clay content. The electrical resistivity is measured for an artificial agar specimen with clay minerals instead of a natural rock. The clay minerals used are Kaolinite and Montmorillonite. Montmorillonite shows remarkably lower resistivity than Kaolinite, although its clay content is fewer than that of Kaolinite. Also, the proposed expression shows a good correlation coefficient as high as 0.89 or more in all clay minerals.