• Journal of Korean Society of Transportation
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• v.16 no.2
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• pp.99-105
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• 1998

이 논문은 포장체 하부구조내 공동(空洞)현상에 대한 위치를 규명하는데 있어서 신속하면서, 간단하고 신뢰성있는 방법을 제시하고자 한다. 동적관입시험(DCP)을 사용하여 콘크리트 슬라브하부의 노상토에 대한 강도를 측정하였다. 타격회수에 대한 침하의 양으로 측정되는 동적관입침하율을 비교하여 포장체하부의 연약지반에 대한 위치를 규명하였다. 콘크리트 포장체 하부의 공동(空洞)현상 및 연약화된 노상토에 대한 정보를 얻고자 하는 엔지니어를 위하여 시험방법 및 결과분석 등을 현장시험을 통하여 체계적으로 설명하였다.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.33-43
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• 2016

In order to analyze ground relaxation and cavity formation mechanism due to deteriorated sewer pipe, field test was carried out and a numerical assessments were compared with the field test results. An artificial underground cavity was intended using the ice block overlaying the buried pipe and confirmed that the cavity and relaxation of the surrounding ground were gradually formed as the ice block starts to melt down. Such mechanism was highly suspected to be involved with soil particle interlocking as a soil compaction was a typical process for the buried pipes. In exploring such mechanism numerically, commercially available DEM (Discrete Element Method) code PFC2D was used and the interlocking induced cavern behaviors were successfully simulated and compared with field test results by utilizing the clump logic imbedded in PFC code.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.165-168
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• 2008

This study performed the 3-dimensional inspection analysis for cavitation by using the ultrasonic pulse velocity method to detect detailed various cavitations in a concrete test material. The internal-void are made of non-void test material and two types of which a regular square type and a rectangle type that produced through the 3-dimensional cavitation to put into a $500{\ast}500{\ast}500mm$ sized non-reinforced concrete test material. The tomography method for the ultrasonic pulse velocity method was used for the non-destructive test. As a result, this study has found that it is possible to visualize the cavitation as an image, and to analyze the internal-void in detail by the non-destructive method.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.599-606
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• 2000

본 연구는 피에조콘(Piezocone) 관입 시험에 의한 과잉간극수압의 소산(Dissipation)특성을 파악하기 위하여, 실측된 소산실험 결과치와 Gupta & Davidson에 의해 개발된 연속 공동확장이론(Successive Cavity Expansion Theory) 모델을 비교하였고, 그 경험적 이론의 적합성을 규명하였다. 연속 공동확장 이론이란, 콘 관입이 유발하는 관입 주변지반의 변환 메커니즘을 연속적인 공동확장의 전개과정로 파악할 때, 관입주변의 연속적 공동확장 영역에서 발생된 과잉간극수압들은 연속적으로 소산되어지고, 결국에는 관입멈춤직후 얻게 되는 소산시험의 결과도 이러한 과잉간극수압의 연속적 소산 메커니즘으로부터 그 영향을 받는다는 개념이다. 본 연구의 실험방법은 Piezocone 관입을 위한 연약모형지반 조성을 위하여 초대형 Slurry Consolidometer에 Slurry를 45일간 압밀시킨후 Calibration Chamber(Louisiana State University Calibration Chamber System)에 옮긴 후 2차 압밀시키는 Two-Stage Consolidation Method를 사용하였다. 또한 모형지반내에 8개의 Piezometers를 설치하여 Piezometers를 설치하여 Piezocone 관입시 유발되는 지반 내에서의 과잉간극수압의 변환을 측정하였다. 실험결과와 이론 예측치를 비교함으로써 연속 공동확장이론 모델은 u$_2$형식의 피에조콘 관입 소산시험 결과들과 잘 들어맞는 모습을 보여줬으나, 관입으로 인한 주변 지반의 과잉간극수압의 소산변화는 정성적으로만 모사 되는 모습을 보여줬다.

• Journal of Biomedical Engineering Research
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• v.19 no.3
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• pp.297-303
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• 1998

The sinus distal to the prosthetic heart valve influences the valve closure behavior and velocity field near the valve, therefore affects the hydrodynamic performance of the prosthetic heart valve. In order to study the effects of valve distal geometry on the hydrodynamic performance of the prosthetic valves, mechanical bileaflet valve(SJMV), monoleaflet polymer valve(MLPV) and trileaflet polymer valve(FTPV) are inserted in the test sections which have the straight and the sinus shape distal to the valve. Leakage volumes and systolic mean pressure drops are measured in the pulsatile mock circulation flow loop. Leakage volumes are slightly less and systolic mean pressure drops are higher in the sinus test section comparing to those in the straight test section, but the differences are statistically insignificant. Flow waveforms are analyzed in order to predict the valve closure behavior. The distal sinus does not affect the closure of the MLPV, but early valve closure of SJMV is observed in the sinus test section. This effect is more significant in FTPV, and the reverse flow peak of FTPV is reduced in the sinus test section. Therefore the sinus distal to the valve can reduce the reverse flow jet caused by sudden valve closure.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.728-732
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• 2004

기존의 지하 공동구 감시 시스템은 광케이블, 누설 동축케이블(LCX), 각종 제어케이블을 사용하여 통신 선로를 구축하기 때문에 시설비가 대단히 고가이며, 여러 가지 통신선로의 이용에 따른 유지보수가 어렵고 시공기간이 길어 시설 확대에 어려움이 있었다. 따라서 통신케이블의 설치 없이 기존에 설치된 공동구의 전등용 저압 전력선을 통신선로로 그대로 이용할 수 있는 전력선 통신 기술을 적용하여 유지보수가 용이한 저비용의 지하 공동구 감시제어시스템을 개발하는 것이 바람직하다. 본 논문에서는 공동구에서의 전력선 통신의 특성을 조사, 시험시스템 설계${\cdot}$제작, 현장실증시험을 통한 성능시험 및 분석을 수행하여 전력선 통신을 적용한 안정적인 공동구 감시제어 시스템을 제안하고자 한다.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.11a
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• pp.67-68
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• 2013

본 연구는 국내 전체 화재발생 건수에서 가장 높은 비율을 차지하고 있는 주거공간에 대한 화재 및 인명안전의 개선 대책에 관한 기초연구이다. 주거공간은 다른 어떠한 방호공간보다 가장 높은 수준의 안전이 요구되는 소방대상물이다. 국내의 주거공간을 대표하는 공동주택의 안전을 확보하는데 가장 중요한 역할을 하는 것이 화재감시시스템이며 이를 구성하는 요소 중에서도 감지기의 성능이 가장 중요한 역할을 한다. 감지기의 성능은 인간의 두뇌와 같은 기능을 하기 때문이다. 이미 일본의 경우는 공동주택 전용의 화재감시시스템을 개발하고 기준으로 제정하여 널리 보급하고 있는 실정이다. 또한 미국은 공동주택 전용의 화재감시시스템이 별도로 존재하지는 않지만 화재특성 및 화재하중 등에 대한 시험을 통해 다양한 방호공간을 효율적으로 적용할 수 있도록 상세한 코드가 정립되어 있다. 따라서 본 연구에서는 국내 공동주택에 적합한 전용 화재감시시스템을 개발하는데 필요한 기초 연구로서 국내와 방재선진외국의 감지기 설치 및 성능을 검증하는데 필요한 설치 및 시험 기준에 대하여 조사하였다.

• Journal of the Society of Disaster Information
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• v.16 no.1
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• pp.60-69
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• 2020

Purpose: Cavity growth process monitoring is to periodically monitor changes in common size and topography for general and observational grades to predict the rate of common growth. The purpose of this study is to establish a systematic cavity management plan by evaluating the general and observational class community in a non-destructive method. Method: Using GPR exploration equipment, the acquired surface image and the surrounding status image are analyzed in the GPR probe radargram in depth, profile, and cross section of the location. The exact location is selected using the distance and surrounding markings shown on the road surface of the initial detection cavity, and the test cavity is analyzed by calling the radar at the corresponding location. Result: As a result of monitoring tests conducted at a cavity 30 sites of general and observation grade, nine sites have been recovered. Changes in scale were seen in 21 cavity locations, and changes in size and grade occurred in 13 locations. Conclusion: The under road cavity is caused by various causes such as damage to the burial site, poor construction, soil leakage caused by groundwater leakage, waste and ground vibration. Among them, indirect factors could infer the effects of groundwater and localized rainfall.

• Journal of the Korean GEO-environmental Society
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• v.15 no.12
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• pp.117-128
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• 2014

Generally, when constructing a tunnel close to existing structures, the tunnel must be built at a constant distance from the structures that is more than width of tunnel to minimize the impact of interference between an existing structures and new tunnel. Spacing of these closed tunnels should be designed considering soil state, size of tunnel and reinforcement method. Particularly when the ground is soft, a care should be taken with the tunnel plans because the closer the tunnel is to the existing structures, the greater the deformation becomes. As methods of reviewing the effect of cavities on the stability of a tunnel, field measurement, numerical analysis and scaled model test can be considered. In the methods, the scaled model test can reproduce the engineering characteristics of a rock in a field condition and the shape of structures using the scale factor even not all conditions cannot be considered. In this study, when construction of a tunnel close to existing structures, the method and considering factors of the scaled model test were studied to predict the actual tunnel behavior in planning stage. Furthermore, model test results were compared with the numerical analysis results for verifying the proposed model test procedure. Also, practical results were derived to verify the stability of a tunnel vis-a-vis cavities through the scaled model test, which assumed spacing distances of 0.25 D, 0.50 D, and 1.00 D between the cavities and tunnel as well as the network state distribution. The spacing distances of 1.0 D is evaluated as the critical distance by the results of model test and numerical analysis.

• Tunnel and Underground Space
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• v.15 no.4 s.57
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• pp.250-263
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• 2005

Progressive and localized brittle failures around an excavated opening by the overstressed condition can act as a serious obstacle to ensure the stability and the economical efficiency of construction work. In this paper, the characteristics of the brittle failure around an circular opening with stress level was studied by the biaxial compressive test using sealed specimen and by the numerical simulation with $PFC^{2D}$, one of the discrete element codes. The occurring pattern and shape of the brittle failure around a circular opening monitored during the biaxial loading were well coincided with those of the stress induced failures around the excavated openings observed in the brittle rock masses. The crack development stages with stress level were evaluated by the detailed analysis on the acoustic emission event properties. The microcrack development process around a circular opening was successfully visualized by the particle flow analysis. It indicated that the scaled test had a good feasibility in understanding the mechanism of the brittle failure around an opening with a high reliability.