• Journal of Korea Water Resources Association
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• v.44 no.6
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• pp.449-459
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• 2011

By examining the experimental results, the critical mean velocity which initiates the movement of riprap is increased with the riprap size in mean diameter, the mean diameter over water depth (d/h), Froude number (Fr), and turbulent shear velocity over critical mean velocity (u*/${\nu}$) which have great correlations among them so these parameters are adopted governing hydraulic stability for riprap. The hydraulic stability equation for riprap is developed by regression analysis. The developed equation is expanded from 0.36~0.73 m/s of experimental range to 0~5.0 m/s for the application in engineering discipline. So many useful relations among those parameters including critical mean velocity are derived by expanding to high Reynolds regions. Mean diameter calculation results by expanding to high Reynolds regions coincide with the calculations of ASCE and USBR at the range of 0~3.0 m/s and the calculation result of ASCE at the range of 3.0~5.0 m/s. The results by developed formulae coincide well with the formulae of ASCE in general and also the results by recently developed existing formulae of hydraulic stability for riprap. Thus, the developed equation has the high applicability in engineering discipline to evaluate the hydraulic stability for riprap.

• Water for future
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• v.28 no.4
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• pp.205-213
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• 1995

Flow in meandering channel is a great concern to civil engineers and may further be characterized as one of the key problems in river morphology. It is difficult to state generalized criteria for channel improvement applicable to any particular river. But it is important to provide some principles and quidelines for the design engineer. The objective of this experimental study is to suggest riprap size, principles and quidelines for the design engineer by the hydraulic model test. For the sake of effective uses for the bank stabilization, hydraulic model tests about riprap weight and size are performed and examing thoroughly. Riprap weight for the upstream of the curvature appex can be computed by U.S.B.R. and Brahms' equation, and the size by Mavis and Laushey's equation. Those for the downstream can be computed using Brahms' and Steinberg's equations, respectively.

• 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 Korea Water Resources Association
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• v.34 no.6
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• pp.753-761
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• 2001

In this paper, the experiments to decide the riprap size for the local scour protection at bridge piers and the coefficients of attack angle were conducted. A formula for the decision of the riprap size and a figure for the coefficients of attack angle were suggested based upon the experimental results. The coefficients of attack angle indicate different values based on the variation of the length-width ratio of bridge pier and the coefficients are increased by the increment of the attack angle. In this paper, the experiments using the piers having the opening ratios of 90%, 92.86% and 95% were conducted. Also, the attack angles 0$^{\circ}$, 15$^{\circ}$, 30$^{\circ}$, 45$^{\circ}$ and 60$^{\circ}$ as well as four different length-width ratios of the bridge pier were utilized. The suggested formula were compared with 6 different formulas and the riprap sizes calculated using the equation suggested in this paper indicate the similar patterns with the formula suggested by Richardson. The suggested formula in this paper can be widely applied in the riprap design for the local scour protection around the bridge pier with the consideration of the attack angle to the flow.

• Journal of Korea Water Resources Association
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• v.33 no.4
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• pp.385-392
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• 2000

An experimental investigation was conducted to determine the effect of a nonuniform pier on the stability of riprap placed around bridge piers. A nonuniform pier is one of which the cross-sectional dimension varies over the length of the pier and comprises a cylinder of diameter bp placed on a larger diameter of foundation bf. and the stability of riprap are significantly influenced by the height of foundation z. The critical height of foundation is defined as the height of foundation which has the same critical velocity to that of uniform pier without foundation, and it was found to be zc=0.8bf. For z

• Ecology and Resilient Infrastructure
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• v.10 no.1
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• pp.1-10
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• 2023

Developmental technique is mixed bio-polymer and riprap to protect the breaking of a levee. Purpose of new technique is restraint from scour and failure of bankside. Technique of this research can apply shore protection and embankment overflow reinforcement works. Because This technique is easy for construction. In order to apply the technique in fields, It is need to conduct the test-bed or real scale experiment study for stability-guaranteed. In case of embankment overflow reinforcement works, It is difficult to conduct test bed in the field. Real scale experiment was conducted in River Experiment Center. Purpose of real scale experiment is to reappear disaster scene by embankment overflow and verify restraint from scour and failure about the technique. In this experiment results, We can find the strength effect of mixed bio-polymer and riprap.

• 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 Korea Water Resources Association
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• v.41 no.8
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• pp.845-854
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• 2008

The old bridge of Woljeong-gyo, which has the fluvial history and culture, represents the ancient construction and civil engineering techniques. It is the oldest stone bridge in Korea and currently restored with its vicinities. In this study, the experimental model was used to analyze the hydraulic characteristics, the local pier-scour depth without scour protection, and the stability of riprap protection using the old grid type panels and stones for Woljeong-gyo of the study area. The water levels were increased around 30cm due to the restored bridge piers and foundations and the effects went up to 200m upstream. The maximum scour depth of 5.4m was measured and the scour protection tests were performed with the riprap size calculated using empirical equations and the existing scour protection range. The riprap of the existing scour protection in the upstream side was broken away, while the riprap of extended scour protection was very stable for the design flood condition of Woljeong-gyo area.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.2
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• pp.38-45
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• 2003

This paper intends to analyze the movement characteristics of the suspended solid(SS) generated in a riprap work which is the most widespread process in harbor construction. The generation and movement behaviors of SS are investigated when 1) basic ripraps (0.001~0.03㎥) are cast for breakwater construction, 2) ripraps are loaded on carrier for riprap casting in the sea-wall construction of dredged material pocket, and 3) ripraps for inner filling are cast. The result of the present study shows that the SS generation is considerable when basic ripraps are cast for breakwater construction and the SS diffusion reaches up to 500m in high tide period. When ripraps are loaded on carrier, the SS is generated by the ripraps running down into sea from carrier, thereby showing a high concentration of SS in the vicinity of carrier. In the surface layer, SS distribution is confined in the vicinity of the carrier due to the prompt sinking of the SS. However the SS in the bottom layer is diffused approximately up to loom and then the SS concentration reaches to the background one. In the riprap (less than 0.03㎥) casting for inner filling using pork crane, SS is diffused approximately up to 300m in the surface layer and more than 300m in the bottom layer. It is quite interesting that the movement of the SS generated in harbor construction is mainly controlled by wind drift in the surface layer and tidal current in the bottom layer, and also the diffusion range of SS in the bottom layer is much larger than that in the surface layer.

• Journal of Korean Society of Disaster and Security
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• v.17 no.2
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• pp.1-11
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• 2024

Most reservoirs in South Korea are earthen dams, mainly because they are cost-effective and easy to construct. However, earthen dams are highly vulnerable to seepage and overtopping, making them prone to sudden failure during excessive flooding. Such sudden failures can lead to a rapid increase in flood discharge, causing significant damage to downstream rivers and inhabited areas. This study investigates the effect of riprap placement on the slopes of earthen dams in delaying dam failure. Delaying the failure time is crucial as it allows more time for evacuation, significantly reducing potential casualties, which is essential from a disaster response perspective. Hydraulic experiments were conducted in a straight channel, using two different sizes of riprap for protection. Unlike previous studies, these experiments were performed under unsteady flow conditions to reflect the impact of rising water levels inside the dam. The target dam for the study was a cofferdam installed in a diversion tunnel. Experimental results indicated that the presence of riprap protection effectively prevented slope failure under the tested conditions. Without riprap protection, increasing the size of the riprap delayed the failure time. This delay can reduce peak discharge, mitigating damage downstream of the dam. Furthermore, these findings can serve as critical reference material for establishing emergency action plans (EAP) for reservoir failure.