• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.157-163
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• 2007

Crack detection technique for concrete structures has been developed in this study. Experimental tests were carried out to detect a surface and internal crack, employing common fiber optic cables and OTDR(optical time domain reflectometry), an optical signal analyzer which is widely used to detect damages at fiber optic cables in the field of optical engineering. While initial concrete crack is ready to occur under cracking force, the occurrence and location of the crack are simultaneously detected to give the same damage to fiber optic cables which have been attached to and/or embedded into concrete in advance. It is obtained through successive tests that the principal factors for crack detection is the covering state of fiber optic cable, and total 4 tests including a preliminary test were conducted and the crack detection technique was verified. The practical usefulness would be expected at crack management and maintenance of concrete structures.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.224-224
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• 2021

광학원격탐사를 통해 취득할 수 있는 초분광 영상은 관련 기술의 발전으로 다양하게 활용이 되고 있다. 특히 초경량 UAV를 기반으로 초분광 센서를 적용한 광학원격탐사는 광범위하게 분포하는 국내 제방의 불안정 요소를 탐지하는데 보다 효과적일 것으로 판단되며 대상에 대한 광역모니터링을 통해 많은 자료를 얻을 수 있고, 고해상도 영상 자료를 활용한 세밀한 분광 및 공간정보 분석이 가능하다. 본 연구에서는 제방 균열 평가를 위해 UAV를 활용하여 안동댐 하류 제방 균열을 대상으로 고해상도 초분광 영상을 취득하였으며, 기 개발된 제방 균열 평가 소프트웨어를 이용하여 조도와 최대강도 데이터에 따른 제방 균열 평가를 실시하였다. 연구지역의 지질은 중생대 백악기의 일직층으로써 적색이암, 셰일, 역질사암 등이 주를 이루고 있으며 제방 내 토양은 대부분 입도가 균일하며 일부 역암이 관찰되는 지역으로 조립토가 주를 이루고 있다. 기 개발된 소프트웨어의 특징은 측정된 데이터를 바탕으로 균열 여부를 판별할 수 있는 프로그램으로써 측정지점마다 별도의 조도와 최대강도 데이터가 주어졌을때, 해당 데이터에 대한 균열 여부를 판별할 수 있다. 주요기능은 제방 균열 여부 판단, 데이터 입력 및 판단을 출력하기 위한 GUI 인터페이스를 제공한다. 연구 결과 제방 균열 평가 소프트웨어를 적용하여 균열과 비균열에 대한 탐지가 가능한 것으로 나타났다. 특히 비균열 포인트의 경우 암석이나 토양의 성질, 빛의 반사에 따라 일부 차이가 있지만 균열은 매우 유사한 반사율 정보를 보이는 것으로 나타났다.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.107-113
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• 2001

This study was conducted preliminarily to develop the crack source location technique for plain concrete beam using acoustic emission(AE). Before the main experiment, the test of virtual An source location was achieved in plain concrete block. The sensor layout was mutually compared between triangular layout and rectangular layout. As the results of test, AE source location by triangular layout was evaluated more effective than that by rectangular layout. The specimen to apply he source location technique was man in total nine specimens (each three in 40 %, 50%, 60% of W/C ratio) which the experiment variable was the compressive strength level(W/C ratio). The bending loading method is selected by cyclic loadings to evaluate the degree of concrete damage. It is seen that Kaiser effect and Felicity effect exists through analysis of AE parameters in coming failure experiment. As a result of analyzing the felicity ratio(FR) values, it is shown that this values can be used for evaluating the degree of concerto damage. AE activity is started highly at the 70% of failure load without the compressive strength level. Thus considered by a index in constructing the system of the failure warning at application of the field structure. And the results compared the real cracking location with the source location has perceived by AE monitoring before it is appeared the primary crack by visual observation.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.155-159
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• 2009

Crack-controlled method which utilizes the dynamic energy such as explosives and propellent gases have been applied to the development of mineral resource and oil and civil engineering. It is necessary to consider the fracture processes associated with the material properties and external forces to control crack propagation using borehole pressure. To investigate the influence of the applied borehole pressure waveform on the crack propagation in rock masses having different material properties, a no-free surface model was used, consisting of a borehole in rock with a continuous boundary. Loading rates ranging from 1 to 100MPa/${\mu}s$ with different rock mass properties was employed to investigate the loading rate dependency of fracture patterns in the rock mass.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 1995.03a
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• pp.92-100
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• 1995

최근 지하 공간의 활용이 증대되는 추세에 이와 관련되어 지하 구조물의 시공전 또는 시공 중에 있어 시공 전략 수립, 장비 결정, 안정성 및 경제성 등을 위해 암반 내의 파쇄대나 균열대의 발달 및 분포에 대한 탐사는 필수적으로 선행되어야 한다. 이러한 탐사에는 분해능이 매우 높은 탐사 기술이 요구되며, 일반적으로 시추공이나 지하 갱도를 이용한 탄성파 탐사나 지오레이다(georadar) 탐사를 많이 사용하고, 자료해석을 위한 역산 기법으로는 지오토모그래피(geotomography)가 필수적인 기법으로 인식되고 있다. (중략)

• Geophysics and Geophysical Exploration
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• v.21 no.3
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• pp.162-170
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• 2018

The purpose of this study is to understand the ground change of large scale mountainous region and to estimate the active weak zone using geophysical exploration (electrical resistivity and refraction seismic explorations) in large scale deep landslide area located in Wanjugun, Jeollabukdo. We also analyzed the characteristics of deep landslides occurred in metamorphic rocks region and confirmed the approximate scale. As a result of comparative analysis of N-value by standard penetration test (SPT), low resistivity anomaly, and tension crack identified from field investigation, a discontinuity in soil layer was estimated at 10 ~ 15 m below the surface. Based on this results, the distribution pattern of active weak zone was confirmed between the discontinuity in soil layer and estimation line of bedrock.

• 한국지구물리탐사학회:학술대회논문집
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• 2010.10a
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• pp.195-198
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• 2010

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.163-171
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• 2009

Subcritical crack growth is one of the main causes of time-dependent fracturing in rock. In the present study, we investigated subcritical crack growth in rock in distilled water (pH = 5.7) and in an aqueous solution of sodium hydroxide (NaOHaq, pH = 12), comparing the results to those in air. We also investigated the effect of the pH in an aqueous environment. We used andesite and granite for all our tests. We determined the relationship between the crack velocity and the stress intensity factor using the double-torsion test under conditions of controlled temperature. We showed that crack velocities in water were higher than those in air, in agreement with other research results indicating that crack velocity increases in water. When we compared our results for NaOHaq with those for water, however, we found that the crack velocity at the same stress intensity factor did not change even though the pH of the surrounding environment was different. This result does not agree with the accepted understanding that hydroxide ions accelerate subcritical crack growth in rocks. We concluded that the pH at the crack tip influences subcritical crack growth, and not the bulk pH, which has little effect.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.15-20
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• 2005

Defects of dam body which can be induced in seepage or leakage procedure can directly affect dam safety. Therefore, a proper inspection method should be carried out in the first place to find out their positions and sizes, After that, some reinforcement works such as grouting and the corresponding assessment could be taken in a proper way. The dam(center core type earth dam) issued in this study has been in need for intensive diagnosis and reinforcement work, because a lot of slumps similar to cracks, seepage and some boggy area have been observed on the downstream slope. High resolution seismic reflection method was performed on the crest profile twice before and after grouting work(Aug. 2001 and Nov. 2004) aimed at the dam inspection and the assessment of grouting efficiency as well. To enhance the data resolution, P-beam energy radiation technique which can reduce the surface waves and hence to reinforce the reflection events was used. Strong reflection events were recognized in the stack section before grouting work, It seems that the events would be caused by e.g. horizontal cracks with a considerable aperture, Meanwhile such strong reflection events were not observed in the section after grouting. That is, the grouting work was dear able to reinforce the defects of dam body. Hence, the section showed an well arranged picture of dam inner structure. In this sense, seismic reflection method will be a desirable technique for dam inspection and for monitoring dam inner structure as well.

• Proceedings of the KSEG Conference
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• 2004.03a
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• pp.16001-16125
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• 2004

물리검층은 주로 석유탐사 분야에서 개발·이용되어왔으나 소구경 시추공을 이용하는 지반조사. 자원평가, 지하수조사 또는 환경오염조사 등에서 물리검층의 수요가 증가하고 있다. 국내에서 수행된 물리검층은 우라늄 탐사 목적으로 1980년 전후로 많이 수행되었으며 1990년 중반에는 지하수 조사에 일부 활용되어 왔다. 현재 물리검층의 활용도가 증가하고 있는 분야는 지반조사 분야로 원위치 물성측정, 시추공과 교차하는 암반의 균열파악 등 터널, 교량과 같은 각종 토목분야의 지반조사에 많이 활용되고 있다. 이외에도 지하수 유동특성 규명이나 환경오염조사, 자원평가(지열, 온천, 석·골재, 금속광상 등)에도 활용되고 있다. (중략)