• Title/Summary/Keyword: Scour

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A Case Study of Scour Vulnerability Evaluation for Shallow Foundations during Floods (홍수시 얕은기초의 세굴위험도 평가 사례연구)

  • Park, Jae-Hyun;Lee, Ju-Hyung;Chung, Moon-Kyung;Kwak, Ki-Seok
    • 한국방재학회:학술대회논문집
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    • 2008.02a
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    • pp.59-62
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    • 2008
  • Scour vulnerability evaluation for shallow foundations was performed to assure bridge safety against scour in the national capital region. The case studies for 26 shallow foundations consisted of site investigation including boring test, bridge scour analysis for the design flood, bearing capacity evaluation of the bridge foundation before and after scour, and comprehensive evaluation of bridge scour vulnerability. Bridge scour vulnerability was determined based on the interdisciplinary concept considering predicted scour depth for the design floods and bearing capacity of foundation as well as dimensions of foundation. Nine of 26 shallow foundations showed the potential future vulnerability to scour with significant decrease in the bearing capacity of foundations due to scour and the remaining 17 were expected to maintain their stability against scour.

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Bridge Foundation and Scour (교량기초와 세굴)

  • 곽기석
    • Proceedings of the Korean Geotechical Society Conference
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    • 2002.11a
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    • pp.168-187
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    • 2002
  • Scour is the physical or chemical attack of flowing water which excavates and carries away material from stream beds and banks. Especially, hydraulic structures such as bridge piers and abutments placed in the channel causes the changes of the flow pattern like acceleration, the formation of vortices, and scour around the structures. Channel scour, especially bridge pier scour is the leading cause of bridge failures. It is very important to apply appropriate methods for both of scour analysis and protection. In this paper, several methods world-widely used for bridge scour analysis and protection are introduced and compared.

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Characteristics of Vortex Structure and Its Shear Velocity in a Scour Hole

  • 김진홍
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.34 no.E
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    • pp.45-59
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    • 1992
  • At downstream part of the hydraulic structures such as spiliway or drainage gate, jet flow can occur by gate opening. If stream bed is not hard or bed protection is not sufficient, scour hole will be formed due to high shear stress of the jet flow. We call this primary scour. Once the scour hole is formed, a vortex occurs in it and this vortex causes additional scour. We call this secondary scour. The primary scour proceeds to downstream together with flow direction but the secondary one proceeds to upstream direction opposite to it. If the secondary one continues and reaches to the hydraulic structure, it can undermine the bottom of hydraulic structure and this will lead to failure of structure itself. Thus, it is necessary to know the physical features of the vortex structure in a scour hole, which is the main mechanism of the secondary scour. This study deals with the characteristics of the vortex structure and its shear stress which causes the secondary scour.

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Experimental Study on Local Scour around Bridge Piers by Scour Protection Devices (세굴보호장치에 의한 교각주위의 국부세굴 실험)

  • 최기봉;김응용
    • Journal of the Korean Society of Safety
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    • v.15 no.1
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    • pp.126-131
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    • 2000
  • This study based on the laboratory works, analyzes factors affecting local scour in order to understand various characteristics of the local scour surrounding bridge piers. Attached with scour protection device as a method for decreasing local scour, it carries out the laboratory experiments and calculates the scour depth. From the experiments attached with the scour protection devices, it seems possible to reduce the scour depth as the protecting plate, column and sacrificial piles are built in the same height with flume bed at pier or footing upstream interrupted falling-flow. And then it could reduce scour depth. The paper presents the following research results: First, the decreasing degree of scour depth is in order of protecting column, protecting plate, sacrificial piles and non-protecting facilities. However, it shows no meaningful difference between protecting column and protecting plate. Second, when $L_p/b$=0.5~1, the decreasing effect of scour depth reached the maximum of 40 percents.

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Scour-monitoring techniques for offshore foundations

  • Byuna, Yong-Hoon;Parkb, Kiwon;Lee, Jong-Sub
    • Smart Structures and Systems
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    • v.16 no.4
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    • pp.667-681
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    • 2015
  • The scour induced by strong currents and wave action decreases the embedded length of monopiles and leads to a decrease of their structural stability. The objective of this study is the development and consideration of scour-monitoring techniques for offshore monopile foundations. Tests on physical models are carried out with a model monopile and geo-materials prepared in a cylindrical tank. A strain gauge, two coupled ultrasonic transducers, and ten electrodes are used for monitoring the scour. The natural frequency, ultrasonic reflection images, and electrical resistivity profiles are obtained at various scour depths. The experimental results show that the natural frequency of the model monopile decreases with an increase in the scour depth and that the ultrasonic reflection images clearly detect the scour shape and scour depth. In addition, the electrical resistivity decreases with an increase in scour depth. This study suggests that natural frequency measurement, ultrasonic reflection imaging, and electrical resistivity profiling may be used as effective tools to monitor the scour around an offshore monopile foundation.

Scour Erosion Around Vertical Embankments and Abutments in a Rectangular Channel (구형수로에서 연직 제방 및 교대 부근의 하상 세굴)

  • 박승우
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.28 no.1
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    • pp.41-50
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    • 1986
  • This paper attempts to qualitatively characterize scour erosion processes near USGS constriction type-I structures with vertical embankments and abutments. The scour dimensions and rates of sand beds around the structure models were measured in a rectangular flume. The test results showed that scour took place at a rapid rate at initial stages, which were followed by a stage of slow and general scour with greater extends. The maximum scour depth was observed near upstream corner of embankments. Empirical relationships for scour dimensions were derived, that were based on the results from a dimensional analysis of scour processes.

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Comparison of Local Scour around Pipeline Caused by Waves and Steady Currents (파랑 및 정상흐름에 의한 해저관로 주변의 국부세굴 특성 비교)

  • Kim, Kyoung-Ho;Oh, Hyoun-Sik
    • Journal of Ocean Engineering and Technology
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    • v.25 no.2
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    • pp.21-28
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    • 2011
  • The primary purpose of the present study was to investigate the mechanism causing scour around a pipeline placed on the seabed in a shallow water zone. Such submarine pipelines are usually exposed to currents and waves. The present experiments made estimates for each different flow type. The scour width and depth in the equilibrium scour phase were analyzed by non-dimensional parameters. The experiment in this study considered various parameters: pipe diameters, wave periods, wave heights, and current velocities. Using the experimental results, the correlations of scour width, scour depth, and main non-dimensional parameters such as the Fr number and KC number were analyzed. In the case of steady currents, the scour hole was closely related to the bottom velocity, while the scour hole in waves showed a relatively low correlation to the bottom velocity because when exposed to waves the scour hole was restricted according to the movement distance of the water particles during a wave period. However, the scour width under a steady current was not limited because vortex shedding was well developed from having enough time and distance.

Dynamic Behavior Analysis of Bridges under the Combined Effect of Earthquake and Scour (지진 및 기초의 세굴을 고려한 교량시스템의 동적거동분석)

  • 김상효;최성욱;이상우;김호상
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2002.03a
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    • pp.187-194
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    • 2002
  • Bridge dynamic behaviors and the failure of the foundation are examined in this study under seismic excitations including the local scour effect. The simplified mechanical model, which can consider the effect of various influence elements, is proposed to simulate the bridge motions. The scour depths around the foundations are estimated by the CSU equation recommended by the HEC-18 and the local scour effect upon global bridge motions is then considered by applying various foundation stiffness based upon the reduced embedded depths. From the simulation results, it is found that seismic responses of a bridge with the same scour depth for both foundations increase due to the local scour effect. The bridge scour is found to be significant under weak and moderate seismic intensity. The recovery durations of the foundation stiffness after local scour are found to be critical in the estimation of the probability of foundation failure under earthquakes. Therefore, the safety of the whole bridge system should be conducted with the consideration of the scour effect upon the foundations and the recovery duration of stiffness should be determined rationally.

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State-of-the-art of Pier Scour Prediction for Design Application

  • Choi, Gye-Woon;Ahn, Sang-Jin;Kang, Kwan-Won
    • Korean Journal of Hydrosciences
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    • v.2
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    • pp.39-59
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    • 1991
  • Scour at bridge pier is a complicated three-dimensional problem involving interaction of fluld force on movable aid nonuniformily distributed sand grains. Although several analytical solution approaches, experimental research and field investigations for scout at piers have been conducted, no comprehensive and universally acceptable solution is so far available. Even though many methods and equations for predicting scour at piers are available in the literature, hydraulic and/or bridge design engineers are often at a loss over which method or equation is applicable for the specific bridge sites. To provide better understanding about scour phenomena and better predicting of scour at piers, intensive research is conducted through comprehensive review of published literature. Based on the research the state-of-the-art of pier scour prediction for design application is provided as a design guide for practicing engineers in this field. Recommendations for applying aggradation and degradation, contraction scour, and local scour prediction methods or equations are suggested. It is hoped that this paper may provide good information for the prediction of scour at piers.

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Monitoring bridge scour using dissolved oxygen probes

  • Azhari, Faezeh;Scheel, Peter J.;Loh, Kenneth J.
    • Structural Monitoring and Maintenance
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    • v.2 no.2
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    • pp.145-164
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    • 2015
  • Bridge scour is the predominant cause of overwater bridge failures in North America and around the world. Several sensing systems have been developed over the years to detect the extent of scour so that preventative actions can be performed in a timely manner. These sensing systems have drawbacks, such as signal inaccuracy and discontinuity, installation difficulty, and high cost. Therefore, attempts to develop more efficient monitoring schemes continue. In this study, the viability of using optical dissolved oxygen (DO) probes for monitoring scour depths was explored. DO levels are very low in streambed sediments, as compared to the standard level of oxygen in flowing water. Therefore, scour depths can be determined by installing sensors to monitor DO levels at various depths along the buried length of a bridge pier or abutment. The measured DO is negligible when a sensor is buried but would increase significantly once scour occurs and exposes the sensor to flowing water. A set of experiments was conducted in which four dissolved oxygen probes were embedded at different soil depths in the vicinity of a mock bridge pier inside a laboratory flume simulating scour conditions. The results confirmed that DO levels jumped drastically when sensors became exposed during scour hole evolution, thereby providing discrete measurements of the maximum scour depth. Moreover, the DO probes could detect any subsequent refilling of the scour hole through the deposition of sediments. The effect of soil permeability on the sensing response time was also investigated.