• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.05b
• /
• pp.1138-1142
• /
• 2005

The tidal river is a river affected by tide, which causes the water level to rise and fall two times everyday periodically. The local velocity across the river could be very fast because of the cross-sectional characteristics of the river even though it's not a rainy season. Therefore extreme local scour could take place around hydraulic structures such as piers and caissons due to backward flow velocity. For the construction of pier foundation of Ilsan-bridge In the Han River, the field observations were performed to get the velocity and water level. The numerical analysis was performed by HEC-RAS(UNET). The relationship between measured maximum velocity and calculated mean velocity is achieved, which is used to estimate the velocity and water level as the construction is proceeding. Countermeasures for scour were designed with the results of the hydraulic analysis to avoid potential damage during construction work. According to the results of monitoring, the velocity increase after temporary road embankment was negligible, from which it is considered that the degradation of main channel compensated for the constriction of cross-section by embankment.

• Journal of Korea Water Resources Association
• /
• v.54 no.12
• /
• pp.1275-1284
• /
• 2021

This paper presents a machine learning technique applied to prediction of time-dependent local scour around bridge piers in both non-cohesive and cohesive beds. The support vector machines (SVM), which is known to be free from overfitting, is used. The time-dependent scour depths are expressed by 7 and 9 variables for the non-cohesive and cohesive beds, respectively. The SVM models are trained and validated with time series data from different sources of experiments. Resulting Mean Absolute Percentage Error (MAPE) indicates that the models are trained and validated properly. Comparisons are made with the results from Choi and Choi's formula and Scour Rate in Cohesive Soils (SRICOS) method by Briaud et al., as well as measured data. This study reveals that the SVM is capable of predicting time-dependent local scour in both non-cohesive and cohesive beds under the condition that sufficient data of good quality are provided.

• Journal of Korea Water Resources Association
• /
• v.34 no.6
• /
• pp.753-761
• /
• 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
• /
• v.41 no.8
• /
• pp.845-854
• /
• 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.

• 한국방재학회:학술대회논문집
• /
• 2008.02a
• /
• pp.477-480
• /
• 2008

Hydraulic experiment was executed to identify the souring range of bride pier. The experiment categorized three kind of bridge pier shape, that is composed of circle shape, square shape and the special shape. Measured scouring data was compared with the results by empirical CSU formula which was generally used in practice. As empirical formula could not consider backfill, measured scouring range is by far smaller than results of CSU formula. Therefore in case of design anti-scouring structure, there is the possibility of overestimation in case of using empirical formula.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.5
• /
• pp.161-170
• /
• 2022

The maintenance of bridges installed in rivers is carried out through facility safety inspection and repair & reinforcement procedures according to the results. Many studies have been so far conducted on the safety check of the bridge upperstructure because of the ease of access. However as it is impossible to directly investigate whether the pier foundation installed in the river has been scoured. Management of underwater foundations has remained based on theory. In this study, the scour of the bridge foundation installed in such a river was realized in 3D form by using an echo sounder and VRS. This made it possible to predict the scour pattern through comparison and analysis with the ground height of the riverbed at the time of the bridge installation. Based on these results, if the pier foundation is used as an initial data to determine whether or not local scour is present and to predict long-term scouring, bridge collapse due to foundation scour can be prevented.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.2B
• /
• pp.111-120
• /
• 2009

A local scour around a bridge pier is known as one of important factors of bridge collapse. Two approaches are usually used in estimating a scour depth in practice. One is to use empirical formulas, and the other is to use computational methods. But the use of empirical formulas is limited to predict a scour depth under similar conditions to which the formulas were derived. Computational methods are currently too expensive to be applied to practical engineering problems. This study presented the application of artificial neural networks (ANN) to the prediction of a scour depth around a bridge pier at an equilibrium state. This study also investigated various ANN algorithms for estimating a scour depth, such as Backpropagation Network, Radial Basis Function Network, and Generalized Regression Network. Preliminary study showed that ANN models resulted in very wide range of errors in predicting a scour depth. To solve this problem this study incorporated cluster analysis into ANN. The incorporation of cluster analysis provided better estimations of scour depth up to 42% compared with other approaches.

• Journal of Korea Water Resources Association
• /
• v.41 no.4
• /
• pp.445-454
• /
• 2008

Many countermeasures for local scour at bridge piers constructed on the river and sea have been developed and researched to protect piers against local scour. The most commonly employed method is riprap protection, which is sometimes required the filter installation between riprap and base layers. However, the construction of stone filters are really hard to perform in the field, require the high cost, or sometimes are impossible. The experimental modeling is conducted to analyze the riprap failure modes and the stability of riprap protection without filters based on the different approach velocity and riprap layer thickness conditions. Also, the stability index to evaluate the performance of riprap protection is developed using the experimental results. The cover and thickness of the riprap layer play a very important role in the stability and thicker riprap layers can prevent a total disintegration of the riprap layer effectively, especially due to winnowing failure.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2007.05a
• /
• pp.1701-1705
• /
• 2007

국부세굴은 수공구조물 주변에서의 국부적인 흐름변화가 그 원인이라 할 수 있으며 이러한 변화는 교각 또는 교대의 하상재료를 굴착하여 이동시키는 침식작용의 결과이다. 이러한 교량의 교각 또는 교대, 그리고 교각을 지지하는 구조물에서 발생하는 국부세굴은 교량의 수명과 안정성에 좋지 않은 영향을 미쳐 재산상의 피해를 줄뿐만 아니라 교량 붕괴 사태 등으로 인한 대형 인명사고를 초래하는 원인이 될 수도 있다. 따라서 국부세굴의 경향을 예측하고 분석하는 것은 교량 구조물이나 수중 구조물의 설계에 있어서 매우 중요한 과업이다. 이러한 국부세굴을 예측하고 분석하는데 있어서 국내에서는 일정한 흐름조건에 대한 최종세굴심을 예측하는데 초점이 맞추어져 있다. 하지만 국부세굴은 하상재료에 따라 세굴이 진행되는 속도가 다르며 세굴의 진행은 시간 의존적인데 반해 국내에서의 국부세굴의 예측과 분석은 최종세굴심 산정에 초점이 맞추어져 있다. 이에 본 연구에서는 보다 실질적이고 경제적인 국부세굴 경향을 예측할 수 있도록 다양한 하상재료에 대한 시간에 따른 세굴 변화의 특성을 파악하고 분석하였다. 이를 위해 하상재료에 따라 수리실험을 실시하였고, 이를 통해 하상재료에 따른 세굴심의 시간적 변화 곡선을 구하였다. 이렇게 구한 하상재료에 따른 세굴심의 시간적 변화 곡선을 통해 하상재료별 평형세굴심 산정하였고, 산정한 평형세굴심과 기존 세굴심 산정공식을 이용하여 입자별 세굴심을 산정하여 비교 분석하였다.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2006.05a
• /
• pp.583-587
• /
• 2006

국부세굴의 발생은 일반적으로 흐름조건, 구조물 조건과 하상재료 세 가지의 주 원인으로 구분할 수 있다. 흐름조건의 경우 구조물 영향으로 발생되는 3차원적인 와류가 주요원인이며 하상재료의 경우 여러 요인이 있겠지만 비중이 같은 입자라 가정할 경우 입자의 크기를 주요 변수로 정할 수 있다. 교각 국부세굴에 관한 연구는 1960년대 이후 연구자들에 의해 매우 다양하게 수행되어 졌으며 많은 산정공식도 제시되었다. 하지만 기존 연구는 최대세굴심 조건으로 다양한 하상재료와 시간에 대한 세굴변동(홍수사상 등)에 대한 영향을 고려하는데 어려움이 있다. 특히 국내의 경우 다양한 하상재료와 홍수빈도를 고려할 때 이에 대한 세굴적용은 매우 중요한 인자라 할 수 있다. 따라서 교각세굴에 대한 궁극적인 목적은 다양한 하상재료와 홍수빈도를 고려할 수 있는 세굴평가를 제안하는데 있다. 이를 위해 본 연구에서는 우선적인 연구로 입자의 다양성과 이미지 기법을 이용한 실시간 측정을 통해 보완하여 입자에 따른 시간적 변화를 분석하였다. 현재 4가지의 하상재료의 입경차이에 따른 국부세굴의 시간적 변화와 초기세굴 발생의 수리적 조건을 파악하고 기존연구와 비교분석하였으며, 이를 기초자료로 세굴심$(S,\;S_{max})$, 교량주변 전단력$({\tau}_p,\;{\tau}_{pc})$, 접근수로부 전단력$({\tau}_a)$와 입자한계전단력$({\tau}_c)$에 대한 시간분석 (time effect)을 통해 다양한 하상재료와 홍수빈도를 해석을 위한 초기분석을 수행하는데 목적이 있다. 수리모형실험에 사용된 가변경사수로의 제원은 $0.6m(W){\times}20m(L){\times}2m(H)$이며 모형구조물은 투명한 아크릴로 제작하였다. 실험방법은 교각 내부에 CC카메라를 전 후면 및 상측면에 설치하여 세굴 발생을 실시간으로 촬영한 후 이미지 분석을 통해 분석하였다.