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1.
桥墩基础冲刷是桥梁毁坏的重要因素,是桥梁基础设计的关键指标之一。目前国内外对于桥墩基础在复杂动力条件下冲刷深度的研究常采用物理模型试验方法,利用正态系列模型方法,在波流水槽中研究了水流、潮流和波流共同作用下青州航道桥索塔基础周围流态变化和局部冲刷特征。研究结果表明,桥墩最大冲刷深度和冲淤范围与水流流速、桥墩轴线与水流夹角和波浪等因素有关;在潮流最大流速和恒定流流速一致情况下,桥墩局部冲刷深度达到平衡后,将会达到与恒定流基本一致的最大冲深;波流共同作用下的最大冲刷深度比恒定流增加10%左右。设计桥墩形状在100年一遇水流和波浪共同作用下桥墩基础局部最大冲刷深度为13.7 m。  相似文献   

2.
Abstract

Because scour is one of the main reasons for bridge failure, this study focuses on accurately predicting the maximum scour depth around different vertical and inclined piers. Scouring is an issue of concern in the bridge design process, as most existing equations for predicting local scour near bridge piers suffer from over- or underprediction issues, resulting in higher foundation costs or bridge failure and inaccurate predictions of the scour around piers. The dimensionless maximum scour depths (ys/D) of vertical and inclined piers were investigated for seven pier shapes with different L/D ratios and four inclination angles (θ) under shallow flow conditions. The inclined pier configuration reduced the ys/D of the piers. The maximum ys/D was observed for a rectangular pier with an L/D of 4.5 in both vertical and inclined configurations (θ of 10, 15 and 21°, respectively). The ys/D was significantly decreased by increasing the angle of the pier from 10 to 30°. The ys/D of the inclined rectangular piers decreased as θ decreased from 30 to 10° and the L/D ratio increased from 1 to 4.5. The best ys/D results were obtained for inclined rectangular piers at a θ value of 30° and an L/D ratio of 7.5 compared to other shapes and inclination angles. New equations were developed to predict the local scour depth for circular, square and rectangular bridge piers. The equations yielded excellent results for predicting the maximum clear water scour depth around vertical and inclined piers with inclination angles of 10, 15, 21 and 30°, respectively.  相似文献   

3.
针对水下桩墩的局部冲刷问题,提出一种适用范围广、防冲促淤效果显著的防护措施。该防护措施把一种相对密度略大于水、几何特征特殊的中性网格结构完全覆盖在冲刷坑或可能出现冲刷坑的床面上,以减弱冲刷坑内水动力,促进泥沙落淤,达到减轻局部冲刷的目的。通过数值模拟和水槽试验探讨了中性网格结构对圆桩周围冲刷坑内水动力及床面形态的影响,并研究了网孔尺寸对防冲促淤效果的影响规律。结果表明:该中性网格结构能显著减小局部冲刷坑内的流速,有效抑制局部冲刷,且对桩前来流来沙的影响微弱。孔径比7.7的网格防护结构可以使无黏性沙床上圆桩的局部冲刷深度减少92%,已存在的冲刷坑则可被修复73%。这些研究成果为桩墩局部冲刷防护提供一种新的思路。  相似文献   

4.
This experimental study presents clear-water scour and deposition patterns around hexagonal arrays of circular cylinders in steady flow conditions. Understanding the scour processes around such configurations could facilitate the design of several hydraulic and marine engineering structures, such as bridge piers and piles. The flow alteration caused by the examined porous obstacles depends on the solid volume fraction of the obstacles and on the angle of attack of the incoming flow, due to the limited number of cylinders constituting the array. Flume experiments with erodible bed were carried out for four array densities (solid volume fractions: 0.14, 0.20, 0.32 and 0.56) under three different orientations (regular, angled and staggered configurations). The scour/deposition characteristics were obtained by means of laser scanner and the results were compared to solid cylinders of equal circumambient diameter. Different angles of attack of the incoming flow lead to different blockage ratios, which have direct impact on the scour characteristics and deposition patterns. The arrays with the higher solid volume fraction generated scour/deposition patterns similar to solid cylinder, while in the arrays with the lower solid volume fractions, local scour around the individual small cylinders became evident. Finally, considering that the load bearing capacity of a pier basically depends on the area of its cross-section, a comparison of the maximum induced scour depth and volume by the cylinder arrays and the solid cylinder with equal solid cross-sectional area is presented, in order to introduce an alternative pier configuration that induces less scour. The results showed that the array of cylinders could generate 27% less scour volume and 22% less scour depth compared to its single solid cylinder counterpart.  相似文献   

5.
6.
针对我国南海某岛礁珊瑚砂地基上的圆形桩基础,采用N-S方程K-s模型、双向耦合方式跟踪流场中颗粒运动轨 迹的方法,对桩周珊瑚砂的冲刷规律进行了求解,分析了桩体周围流体的速度场以及桩体表面剪应力场的分布规律,同时对桩周珊瑚砂冲刷坑的形成过程进行了模拟。计算结果表明,在桩体周围形成的马蹄形漩涡和桩柱后方的尾涡作用下,桩周土体出现了较为明显的冲刷现象,涡旋的释放显著地影响着珊瑚砂地基上桩基的冲刷坑形状;而且,由于珊瑚砂颗粒密度较石英砂小,水动力作用下桩周冲刷坑更容易形成,所以实际工程中需要考虑有效的防护措施。  相似文献   

7.
Experimental Study on Local Scour Around Bridge Piers in Tidal Current   总被引:8,自引:1,他引:7  
Local scour around a bridge pier is an important pm‘mneter for the design of a bridge. Compared with the local scour in a mono-directional current, the local scour in a tidal current has its unique characteristics. In this paper, several aspects of local scour around bridge piers in tidal current, including the scour development process, the plane form of a scour hole and the maximum scour depth, are studied through movable bed flume experiments.  相似文献   

8.
1 .IntroductionWiththedevelopmentofexploitationofmarineresources ,theconstructionofoffshorestructuresdevelopsrapidly ,suchasmarineoilplatforms ,deep waterbreakwaters ,marinebridges ,largehar bors,etc .Thesestructureswillchangesurroundingwaveandcurrentconditionsandleadtolocalscourofseabed ,resultinginstructuraldamage .Therefore ,localscouraroundmarinestructuresaswellastheirprotectionhasdrawnmuchattentionfromrelativeengineeringfields .Manyscholarshaveconduct edtheoreticalanalysisandexperimentals…  相似文献   

9.
Bridge scour is recognized as one of the key factors that causes structure failures, which in turn leads to economic and life loss. In this study, flume tests of four typical arrangements of pier groups embedded in sand under steady clear water conditions were carried out to observe the process and maximum depth around piles of scour. The investigation included single pile, tandem piles, side-by-side piles, and 3 × 3 pile groups. Different conditions including different pile spacing, flow velocity, and water depth are considered. Moreover, the evaluation of design methods from the United States, New Zealand, and China was analyzed and compared through experimental and mathematical methods. The experimental results show that shielding and jetting effects are obvious in pile groups, which become less obvious with the increase of pile spacing. The dynamic process of scour around single pile and pile groups are quite different. Meanwhile, most of the predicted scour depths by these equations tend to be much larger than those from field data, which may lead to overdesign and consequently high construction cost. In addition, data from this study and some laboratory experiment data from previous work were used to derive the correction factors of a new scour prediction equation, which can be used to estimate the scour in a sand bed and agree well with the observations.  相似文献   

10.
Abstract

Sediment has a severe effect on bridge stability, and time-domain reflectometry (TDR) is a suitable method for assessing scour depth. This paper presents a fundamental study to demonstrate the suitability of a circular TDR system to enhance the resolution when monitoring scour depth with consideration of detailed local changes over a wide area around piers. A total of 32 electrodes are vertically installed on a cylinder pier around the circumference at ~7.36?mm intervals. Scour depth is investigated through small-scale laboratory experiments, where a measured waveform reflects the artificially constructed scour depth with high resolution (≈5?mm). Different scour types including circular, mushroom, elliptical, and irregular shapes are developed to verify the application of circular TDR, and shapes are predicted through the detailed local distribution. The influences of the reflected waveform according to water level change, temperature variation, and salinity effect are investigated as additional considerations, and the relative deviation of scour depth is analyzed. This study demonstrates that the proposed circular TDR system achieves better resolution than existing single TDR systems and may provide a better alternative technique for monitoring scour depth.  相似文献   

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