• KCID journal
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• v.2 no.2
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• pp.37-45
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• 1995

In this study, formulae related tidal current-stone diameter and weight have been analyzed based on the real sea dike construction situation. Three formulae which denoted Shields, Isbash and Netherlands's simple method have been compared by the various ti

• Journal of Korea Water Resources Association
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• v.49 no.12
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• pp.1035-1044
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• 2016

In joint portions of the levee and the barrier, complex 3-dimensional flow was generated and collapse of revetment occurred frequently. For these reasons, it is necessary to install the joint revetment with greater stability as compared with the general revetment at the joint portions. However, design criteria for joint revetment was not presented in River Design Criteria (KWRA, 2009). Therefore it is necessary to research for engineering design of the joint revetment. In this study, hydraulic experiments were performed under various flow conditions in order to realize the collapse conditions of riprap and carried out in 20.0 m straight open channel with one side levee and the width was 4.0 m. The diameter of riprap covered around joint revetment was 0.03 m and the inlet discharges were $0.5{\sim}0.8m^3/s$. The numerical simulations were performed under same conditions with experiment. as results of this numerical simulations, the influence range was confirmed from the distribution of flow characteristics and shear stress. As a result, the riprap diameter of the joint revetment was calculated from 4.1 to 6.9 times greater than that of general revetment. As the inlet discharge was large, the range of vulnerable area was developed long in the downstream direction despite of same withdrawal velocity of riprap. Through this study, the methods of calculating the riprap diameter and influence range were proposed according to hydraulic characteristics of flow around joint revetment. At a later study, if additional experiments about effect of flood plane and various types of barrier is applied, it is expected that rational design method with stability of joint revetment can be proposed.

• Journal of Korean Society of Disaster and Security
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• v.11 no.1
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• pp.31-38
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• 2018

The 99.1% of small dam and most of the levees in Korea are soil dam which can be constructed with lower cost and less effort compared with ones made of concrete. However, they are so vulnerable to overflow. Sudden collapses of these strucrues lead to increase flow rate rapidly, which may cause catastrophic problems in downstream regions. In this study, the experimental study on the collapse delay effect of riprap that was laid on slope of soil levee was carried out. A prismatic rectangular open channel was used and three different sizes of the riprap were installed on slope of a scaled earth dam. A new formula for the collapse time of the levee with the installation of riprap was presented, using the previous researches and the dimensional analysis. In this process, an unsteady flow condition was considered to derive the deviation time of the riprap. And additional experiments were conducted to understand the effect of reinforcement of riprap, and it was found that the reinforcement of riprap was more effective than twice sizing of intial riprap. If the collapse time is delayed, EAP (Emergency Action Plan) and forecasting can greatly reduce the degree of flood damage. Also, it will be meaningful that the results of this study are used for river design.

• Journal of Korean Society of Disaster and Security
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• v.12 no.1
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• pp.57-66
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• 2019

One of the most serious problems with concrete small dams or barriers installed in small/median rivers is the deposit of sediments, especially, in Korea. An effective way to discharge such sediments to downstream is to construct a bypass pipe under the river bed. However, efficiency may become lowered if ripraps are entered into the bypass pipe. Therefore, in this study, we derived the threshold condition for the exclusion of ripraps from the bypass pipe using 3D numerical analysis. Upstream flow of the small dam was assumed to be stationary, and the energy concept was applied to the control volume containing the bypass pipe and its periphery. As a result, when the ratio of the water level difference between upstream and downstream to the diameter of the riprap was approximately equal to 1.2, the threshold condition for exclusion of the stones or riprap from the bypass pipe was affirmatively determined. If the characteristics of the adsorptive sediment adversely affecting the river environment in the future would be taken into account, results from this study are expected to put to practical use in the management of concrete small dam with bypass pipe system.

• The Journal of Engineering Geology
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• v.12 no.1
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• pp.89-93
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• 2002

Seismic geotomography method was performed to verify rock-filled settlement and its stability in No.38+0 profile and No.40+0 profile. The velocity distributions of geotomography method expressed the quantitative value of the ground conditions. The rock-filled layer and in-situ sediments layer are clearly divided on the basis of seismic velocity 2100 m/sec which is derived from the results of seismic geotomography and boring. Current rock-filled settlement conditions are somewhat different from designed settlement estimation line. Seismic geotomography represents current settlement conditions as a quantitative analysis.

• Journal of Korea Water Resources Association
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• v.33 no.6
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• pp.725-731
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• 2000

Experimental studies were conducted in a clear water condition to investigate the functioning of a sack gabion as a scour countermeasure at bridge piers. For different sizes of fill materials of sack gabions no difference was observed in the initial movement of sack gabions. Significant factors on the dislodging of sack gabions are approaching flow depth and velocity, pier width, and thickness and length of sack gabions. It was observed that the stability of the sack gabions is increased in a collective body of riprap stones than the placement of individual riprap stone. The length of a sack gabion has significant effect on its initial movement and the stability of a sack gabion was found to be increased by lengthening the length of gabions. The experimental results were used to derive formulas sizing gabions for scour protection at bridge piers. piers.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.4
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• pp.319-326
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• 2001

This paper reports on a recent investigation to determine criteria for the design of rubble-mound breakwaters. Existing theories and empirica] equations have been carefully reviewed and a new relation is proposed for the determination of optimum weight of armor unit of rubble-mound breakwater. A new parameter is introduced into the new semi-theoretical equation, which is closely related with the surface particle velocity of wave motion. The laboratory data reported by van der Meer(1987) were used for the determination of proper relations of empiricat parameters introduced into the new empirical equation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.4
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• pp.413-420
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• 2008

Wave force is an important factor which gives a direct affect to stability of the rubble mound breakwater. Particularly wave force has been considered as the main cause of displacement for replaced rubble mound breakwater which permits a little displacement to some degree. But the effect on displacement by wave force has not been considered and reflected in design. Therefore in this study, we compared numerical analysis displacement with field measured displacement so that the effect of wave force on displacement can be reflected in design. Result of the numerical analysis displacement was well consistent with field measured displacement data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.127-136
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• 2011

The settlement of a compaction plate resting on the surface of rubble-mound and subjected to a vibrating vertical load can be characterized by a transient amplitude and a plastic settlement. As long as the maximum imposed load does not exceed the bearing capacity of the rubble-mound, plastic settlement will approach an ultimate value and essentially steady-state vibration will ensue. For the settlement behavior by vibro-compaction, most laboratory experiments were conducted on laterally confined samples with loads over the full surface area or on samples placed on a vibrating table. In the field, the loads cover only a small fraction of the surface area. In this study, crushed stones are loaded with the same as field condition. According to the vibro-compaction experiments on crushed stone, it was found that approximately 90% of total settlement occur within 2 minutes and plastic settlement increases with increasing cyclic stress levels including static and dynamic stress. A compaction equation on which the number of load cycles, amplitude of plate, settlement, width of plate, and cyclic stress are related each other is proposed.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.28-31
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• 2010

충청남도 서해안은 생태환경의 보고로서 갯벌, 사구, 해안습지 등 독특한 자연적 특성을 갖고 있는 지역이다. 그러나 다른 지역에 비해 대규모 간척 및 매립으로 인한 해양생태계 피해에 현저히 노출되어 있고, 최근 산업화 및 관광권화가 진행되고 있으며 해안선 침식 방지를 위한 연안정비사업으로 각종 연안 방호구조물이 건설되었다. 이 중 가장 많이 건설된 연안 호안구조물은 배후지역의 안정성 확보, 해안도로의 건설 등 다양한 목적으로 축조되었다. 그러나 성장위주의 경제정책으로 연안 호안구조물이 무분별하게 설치되어 파도와 호안 구조물의 접촉 시 호안구조물이 파랑을 견디지 못해 사면피복재가 산란되어 외관상 주변 환경을 해칠 뿐만아니라 2차 피해까지 야기 시킬 우려가 있다. 본 연구에서는 호안구조물의 리모델링을 통해 안정성을 증대시키기 위해 서해 연안지역의 4개 시 군 29개 지점을 대상으로 호안구조물 현황에 대해 조사하고 호안구조물의 리모델링을 통해 붕괴된 지역을 대상으로 파랑에 대해 안정한 사석재 소요질량을 호안구조물의 경사 별로 산정하여 비교하였다. 피복재 소요질량 산정을 위한 설계파고는 유의파고를 적용하였으며, 산정공식은 허드슨공식(Hudson, 1959)을 사용하였다. 추가적으로 사석 층의 두께와 단위면적당 수용해야할 사석재의 개수를 산정하여 호안구조물 설계 시 사석재의 배치를 용이하게 할 수 있도록 하였다. 본 연구에서 산정된 값들은 초기설계로서 파랑에 안정한 호안구조물의 설계 조건 중 일부분으로 호안구조물의 최종 설계 시 조파실험을 통하여 안정성을 검증 해야 할 것으로 판단된다.