• The Journal of Engineering Geology
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• v.29 no.3
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• pp.289-302
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• 2019

As the occurrence of ground subsidence near the excavation site increases recently, studies are being conducted to predict the possibility of ground subsidence prior to excavation. In this study, the ground subsidence risk rating for pre-excavation (GSRp) developed by the previous study was applied to actual excavation sites to verify its applicability. The final results for the evaluation of the ground subsidence risk level for five excavation sites revealed that GSRp scores were calculated between 40 and 79 points and classified mainly into grades II (Good Ground)~III (Fair Ground). In order to verify the evaluation method, the obtained GSRp grades were compared with the measured horizontal displacements. The horizontal displacements measured in five excavation sites were between 25% and 47% of the allowable displacement, which were well agreed with the low subsidence risk level obtained from GSRp calculation. It is expected that the GSRp method can be used as an evaluation tool for predicting the risk of ground subsidence before excavation if GSRp is verified and supplemented through the additional research for the poor soil with the high risk of ground subsidence.

• Journal of the Korean Geotechnical Society
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• v.34 no.8
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• pp.27-36
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• 2018

The collapse behavior of ground subsidence caused by continuous loss of particles depends on the saturated condition and density of the ground. In this study, types of ground subsidence were classified based on the saturated condition and each type was performed on the different relative density to analyze the influence factors on the collapse behavior by distinct element method. According to analysis results, the relatively small amount of settlement occurred on the dense ground and a cavity was created under dense-unsaturated ground. In contrast, loose ground showed the large amount of settlement and collapsed immediately without cavity formation even if the unsaturated ground was simulated. The results demonstrated that because the relative density has influence on the mechanical interlocking and saturated condition has influence on the inter-particle force, these are important factors to change the collapse behavior.

• Journal of the Korean GEO-environmental Society
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• v.19 no.11
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• pp.23-30
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• 2018

According to recent ground collapse occurrence, ground subsidence is increasing every year in downtown area, which is a social problem. The purpose of this study is to investigate the relationship between ground water level lowering and ground collapse through laboratory model experiments. After mixing 1:1 granite weathered soil with sand, sandy soil was formed as a relative density of 30%, 50%, and 80%. And then the changes of soil discharge with change of groundwater level were compared. The physical property of material of which particle distribution were well graded with maximu dry unit weight of $1.94kg/cm^3$ and internal friction angle of 37degrees. Ground water levels were measured at 10 cm, 20 cm, and 30 cm from the bottom. As a result, the experiment shows that the higher the groundwater level works the higher the discharge velocity and the magnitude of underground cavity also increases with elapsed time. Finally, the cumulative quantity of soil discharge occurred up to 30 kg at the elapsed time, 35 minutes. It was also confirmed that the range of ground collapse increased due to soil discharge with ground water level lowering.

• Journal of the Korean GEO-environmental Society
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• v.18 no.5
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• pp.35-43
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• 2017

It is a method of suppressing back ground subsidence by re-injecting groundwater back to the target ground and recovering the underground water level. In order to analyze the subsidence of the back ground due to maintaining the underground water level, indoor model experiments were conducted. Through this study, the factors influencing on the groundwater and the tendency of subsidence back ground by experiments were analyzed and the effect of ground subsidence by reinfusion of groundwater was also investigated. As a result of the subsidence analysis with considering only the influence of the underground water level, the settlement of the ground occurs as the underground water level at the time of ground excavation goes down. The closer to the back of the retaining wall, the maximum settlement occurred. Moreover, it was analyzed that the influence distance where subsidence occurs from retaining wall to the point of about 1.8 H on the basis of the ground collapse. The most effective location of water reinjection is the closet location to the back of braced-cut wall for reducing the groundwater down and also minimizing the ground settlement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.235-253
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• 2018

Groundwater flow induced by cracks in a buried pipe causes ground loss in the vicinity of it which can lead to underground cavities and sinkhole problems. In this study, the ground collapse mechanism and the failure mode based on an aperture in the pipe located in cohesionless ground were investigated through a series of physical model studies. As the influence parameters, size of the crack, flow velocity in the pipe, groundwater level, ground cover depth and ground composition were adopted in order to examine how each of the parameters affected the behavior of the ground collapse. Influence of every experimental condition was evaluated by the final shape of ground failure (failure mode) and the amount of ground loss. According to the results, the failure mode appeared to be a 'Y' shape which featured a discontinuous change of the angle of erosion when a groundwater level was equal to the height of the ground depth. While in the case of a water table getting higher than the level of ground cover depth, the shape of the failure mode turned to be a 'V' shape that had a constant erosion angle. As the height of the ground depth increased, it was revealed that a mechanism where a vertically collapsed area which consisted of a width proportional to the ground height and a constant length occurred was repeated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.217-226
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• 1993

This study is related to the surface subsidence due to the collapse of a underground void during earthquakes. The amount of the settlement due to the collapse of a underground void will depend on the depth of the void, the initial condition of unit weight of sand, the size and type of foundation, the strength of earthquake, the size of a void, etc. The purpose of the paper is to estimate the amount of the subsidence, analyse the factors affecting the subsidence, and develop a program determining the probability of the damages to structures in terms of absolute and differential settlement and rotational settlement. On the base of the results obtained in this study, when the depth of a void is constant and the width of the void increases, the change of the subsidence factor due to the angle of internal friction and the actual effective factor of the void become smaller than that due to the unit weight of sand deposits. In the same condition, the probabilities of damages due to the absolute and differential settlement increase, and those due to the rotational settlement decrease.

• The korean journal of orthodontics
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• v.26 no.5 s.58
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• pp.637-645
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• 1996

In non-growing Class III malocclusion, the critical aspects which determine the need of orthognatic surgery are the severity of skeletal discrepancy, incisor inclination, overbile and soft tissue profile. Two-jaw surgery is more effective in correcting severe sagittal, vertical, transverse skeletal discrepancies and facial asymmetry. And more esthetic and stable profile can be achieved by two-jaw surgery Some midfacial deficiency Patients can be treated by Pyramidal Le Fort II osteotomy to maintain infraorbital rim and malar complex and to advance nasomaxillary complex. Others who require advancement of infraorbital rim and malar complex can be treated by quadrangular Le Fort II osteotomy. On the following cases, patients who had represented midfacial deficiency and mandibular prognathism were treated with combined orthodontic-surgical therapy by Le Fort II osteotomy and BSSRO.

• Journal of the Korean GEO-environmental Society
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• v.16 no.12
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• pp.13-22
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• 2015

Developed ground cavity due to leakage of decrepit old sewer pipe causes ground surface settlement and brittle fracture of pavement. Recently, for 5 years, frequency of occurrence of ground subsidence phenomenon tends to increase rapidly and/or steadily. It is difficult to investigate ground surface settlement and/or subsidence in urban area because most ground surfaces are covered with asphalt or concrete pavement. In this research, therefore, ground surface settlement, influence zone and settlement of sewer pipe were analyzed using finite element method. Not only reinforced effect of pseudo-plastic backfill that is applied to prevent ground surface settlement or subsidence spot, was compared and analyzed using numerical analysis program, but also direct shear test was carried out to determine strength parameters of pseudo-plastic backfill.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.139-148
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• 2017

Ground subsidence caused by damaged water pipe and sewer is recently increasing due to the aging of city and pipeline in many city. Although many recent studies have verified characteristics of ground subsidence due to wastewater pipe breakdown, research about characteristics of ground subsidence due to water pipe is insignificant. subsidence due to water pipe is insignificant. This study aims to identify the ground failure mechanism caused by water and sewer pipe breakdown. Accordingly, we conducted an indoor model experiment to verify characteristics of ground subsidence considering characteristics of ground and ground failure. The water pipe pressure and velocity head was considered to find out ground subsidence mechanism. Also comparative analysis is conducted by analyzing relative density and fine-grain content considering embedded condition of water pipe. When the relative density and seepage pressure is low, small scale ground subsidence can occur, but when the conditions are opposite, ground subsidence occur in large scale and expands to ground level over time. Furthermore, it is acknowledgeable that ground cavity that is formed after soil run off due to seepage in deep earth, maintains steady strength and stays on the ground level for long period.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.30-30
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• 2007

현재 다양한 종류의 RF 통신 제품이 시장에 등장하면서 제품의 경쟁력 확보에 있어 소형화 정도가 중요한 이슈가 되고 있다. Passive Device는 RF Circuit을 제작할 때 많은 면적을 차지하고 있으며 이를 감소시키기 위해 여러 연구가 진행되고 있다. 가장 효과적인 방법으로 반도체 집적기술로 크기를 줄이는 방법이 있으나, 공정이 비싸고 제작 시간이 오래 걸려 제품개발 시간과 개발비용이 상승하게 된다. 반면에 SoP-L 공정은 PCB 제작에 이용되는 일반적인 재료와 공정을 사용하므로 개발 비용과 시간을 줄일 수 있다. SoP-L의 또 하나 장점은 다종 재료를 다층으로 구성할 수 있다는 점이다. 최근 chip-type의 Device를 PCB 기판 안에 내장하는 방법의 RF Circuit 소형화 연구가 많이 진행되고 있다. 본 연구에서는 SoP-L 공정으로 chip-type 수동소자를 PCB 기판 내에 함몰하여 수동소자회로를 구현, 분석하여 보았다. 수동소자회로는 880 MHz~960 MHz(GSM) 영역과 1.71 GHz~1.88 GHz(DCS) 영역을 나누는 Diplexer를 구성하였다. 1005 size의 chip 6개로 구현한 Diplexer를 표면실장과 함몰공정으로 제작하고 Network Analyzer로 측정하여 비교하였다. chip 표면실장으로 구현된 Diplexer는 GSM에서 최대 0.86 dB의 loss, DCS에서 최대 0.68 dB의 loss가 나타났다. 표면실장과 비교하였을 때 함몰공정의 Diplexer는 GSM 대역에서 약 0.5 dB의 추가 loss가 나타났으며 목표대역에서 0.6 GHz정도 내려갔다. 이 결과를 바탕으로 두 공정 간 차이점을 확인하고, 함몰공정으로 chip-type 수동소자를 사용하였을 때 고려해야 할 점을 분석하였다. 이를 바탕으로 SoP-L 함몰공정의 안정성을 높여서 이것을 이용한 회로의 소형화에 적용이 가능할 것으로 기대한다. 특히 능동소자의 DC Power Control에서 고용량의 수동소자를 이용할 때 집적도를 높일 수 있을 것이다.