共查询到18条相似文献，搜索用时 125 毫秒
1.
长江口沙波分布区桥墩局部冲刷深度计算公式的改进 总被引：1，自引：0，他引：1
利用多波束水深仪、浅地层剖面仪和多普勒流速仪对长江口苏通大桥南、北主墩区域现场测量,结果显示主墩周围最大冲刷深度为8.3 m和19.6 m。建墩前后河床形态变化显著,建墩后桥墩所在床面由平床改变为典型不对称沙波发育,平均波长为30.8 m和23.1 m,平均波高为4.2 m和9.4 m,陡坡朝向下游。基于实测水文条件和地形资料,以沙波起动流速和落急最大流速分别取代单向流作用下"平床"假定的桥墩局部冲刷计算公式中单颗粒泥沙的起动流速和墩前流速,获得河口涨落潮双向流作用下沙波底床桥墩局部冲刷计算公式。且该公式计算的苏通大桥南、北主墩局部冲刷深度为9.5 m和22.1 m,非常接近实测值。 相似文献
2.
利用多波束水深仪、浅地层剖面仪和多普勒流速仪对长江口苏通大桥南、北主墩区域现场测量,结果显示主墩周围最大冲刷深度为8.3m和19.6m.建墩前后河床形态变化显著,建墩后桥墩所在床面由平床改变为典型不对称沙波发育,平均波长为30.8m和23.1m,平均波高为4.2m和9.4m,陡坡朝向下游.基于实测水文条件和地形资料,以沙波起动流速和落急最大流速分别取代单向流作用下“平床”假定的桥墩局部冲刷计算公式中单颗粒泥沙的起动流速和墩前流速,获得河口涨落潮双向流作用下沙波底床桥墩局部冲刷计算公式.且该公式计算的苏通大桥南、北主墩局部冲刷深度为9.5m和22.1m,非常接近实测值. 相似文献
3.
金塘大桥桥墩附近的海床冲刷 总被引：2，自引：0，他引：2
东起舟山市金塘岛的沥港镇,跨越灰鳖洋,西至宁波市镇海区新泓口的金塘大桥,为舟山大陆连岛工程的主体.大桥全长为18.5 km,海面桥墩近350个,桥墩附近海床冲刷深度主要包括因风浪和潮流引起的自然冲刷、因建桥使过水断面缩窄而产生的一般冲刷和桥墩阻水形成的马蹄形漩流引起的局部冲刷.河流上桥墩局部冲刷已进行过大量研究,建立了可供设计使用的桥墩冲刷计算公式,而金塘大桥位于灰鳖洋海域,作用水流为极其复杂的往复流,使海床局部冲刷深度难以利用现有公式进行计算,因此采用海域实测地形资料分析了桥轴线附近的海床自然冲刷,利用水槽正态模型试验模拟研究了桥墩附近的一般冲刷和局部冲刷.实测资料表明,该海域潮流流速大小与潮差有较好的相关关系,潮差越大,潮流流速也越大,而桥墩的局部冲刷深度也随流速的增大而增大,因此,选取潮差频率为300年一遇和10年一遇的特大潮分别作为运行期和施工期的潮流边界.桥位所处的海床较为稳定,故以最新的实测地形各桥墩处高程作为冲刷试验起始高程.试验初期桥墩附近海床快速下切形成冲刷坑,随后冲刷值迅速减小,海床渐趋稳定.研究表明,该大桥所处海域总体上趋于动态平衡状态,桥轴线东段微冲、西段微淤.运行期金塘大桥附近的海床自然冲刷,一般均在1.1 m以内,仅在主槽附近较大,约5 m左右.试验表明,潮流作用下桥墩附近的一般冲刷和局部冲刷均明显大于自然冲刷幅度,主墩最大局部冲刷幅度为14.4 m,引桥桥墩最大局部冲刷幅度为7.8～10.3 m;据此可得到桥墩附近海床的总体冲刷幅度和设计高程,不仅为工程建设、运行的安全性及经济性提供了坚实的技术支撑,而且可供其它海域建桥后桥墩附近海床的冲刷研究提供参考. 相似文献
4.
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
5.
长江大桥桥墩受水流冲刷和泥沙淤积的影响,需要定期对桥墩水域地形进行监测和分析。结合安庆长江公路大桥水域监测实例,阐述了使用多波束测深系统和声学多普勒流速剖面仪(ADCP)对大桥水域进行联合监测,采用GIS软件对大桥水域地形进行冲淤计算,并制作了桥墩的立体图和大桥区域的水域冲淤变化图,分析了桥墩及附近水下地形与水流的变化,对桥墩的冲刷研究具有非常重要的意义,监测成果为大桥的安全运营提供了有益的安全保障。 相似文献
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7.
本研究通过对胶州湾大桥建成前后湾内泥沙冲淤情况进行模拟。探讨了典型时刻胶州湾大桥附近海域的海流流速和流向情况。对比胶州湾大桥建成前湾内的流场模拟结果可知,胶州湾大桥的建设对胶州湾内整体的海流流态影响较小。胶州湾大桥的建设对胶州湾水动力的改变主要在桥墩建设附近海域。通过大桥建设前后冲淤数值模拟结果可知,工程前后工程附近冲淤趋势基本一致,只是在大桥桥墩附近出现冲淤变化较大的情况,表现为在桥墩的南北两侧出现较大桥建设前淤积加强区,在桥墩的东西两侧出现冲刷加强区,在通航孔桥墩跨度较大的海域,冲刷强度增大比较明显。 相似文献
8.
本文根据石臼港煤码头引桥桥墩周围的局部冲刷的三次实测资料,研究了波浪与潮流共同作用下孤立建筑物周围的局部冲刷问题,发现一种在波浪与潮流同向的下游形成二个深度基本相同、位置明显对称的冲刷坑的新的冲刷形态。 相似文献
9.
海流作用下海底管道局部冲刷数值分析 总被引：1，自引：0，他引：1
在任意拉格朗日-欧拉参考坐标系下,采用基于雷诺平均的Navier-Stokes方程组(RANS)、流线迎风有限元方法、泥沙输运模型以及底床变形方程,对海流引起的海底管道局部冲刷进行了数值模拟。着重讨论了均匀来流流速和海底管道直径对局部冲刷发展过程及平衡冲刷深度的影响作用。数值结果表明,在冲刷的初始阶段,冲刷深度随时间迅速增加,之后缓慢逼近极限平衡深度;在管径一定的情况下,管道附近的局部平衡冲刷深度与流速大致呈线性关系;当流速超过某一临界区域后,最大平衡冲刷深度出现的位置并不在管道正下方,而是随流速的增加向管道下游方向移动;另外,管道直径也会对平衡冲刷深度产生比较明显的影响,在相同流速下,平衡冲刷深度大致随管径呈线性增大。在本文的计算范围内,海底管道的相对局部平衡冲刷深度基本随雷诺数线性增加,但流速对冲刷深度的影响作用要比管径的影响作用更为明显。 相似文献
10.
为探究台阶式沉井基础附近局部冲刷的影响,建立三维水动力数学模型,计算分析恒定流下台阶式沉井基础附近水动力特征。基于数值模拟结果设计了8个有效试验工况进行物理模型试验,分别探究了台阶式沉井平台宽度、埋置深度以及挡墙高度对局部冲刷特性的影响并进行讨论。试验结果表明台阶式沉井局部最大冲刷深度随平台截面宽度比增大逐步减小并趋于稳定。台阶式沉井局部最大冲刷深度随平台埋深比增大而逐步减小最终趋于稳定。台阶式沉井平台处设置较低挡墙对减小沉井周围局部冲刷最大深度有小幅的效果。 相似文献
11.
A laboratory study of local scour at complex piers under steady clear-water conditions is presented. The term complex piers is used to define a bridge pier comprising of a column, pile cap, and pile group. Comprehensive data over the full range of possible pile cap elevations for complex piers with different geometries were obtained using five complex pier models, which were scaled down from existing bridges in Malaysia. The data are used to evaluate existing methodologies for characterizing the effective width of complex piers with varying pile cap location relative to the undisturbed streambed. The effect of pile cap location on scour depth is also addressed. To improve the predictions of local scour at complex piers, the new data and some previous data are used to propose a new method to predict local scour depth at complex piers. 相似文献
12.
H. Omara G. M. Abdeelaal K. Nadaoka A. Tawfik 《Marine Georesources & Geotechnology》2020,38(2):133-143
AbstractBecause 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
13.
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
14.
The reliable estimation of the local scour depth at a bridge pier is essential for proper design and maintenance of bridge piers. Most local scour formulae have been developed based on the results of laboratory experiments. The formulae based on laboratory data do not often produce reasonable predictions for field piers because laboratory investigations are apt to oversimplify or ignore many of the complexities of the flow fields around the bridge piers. Validation of the formulae is necessary in order to ascertain which of the formulae are able to provide reasonable estimates of the local scour depth. In this study, six commonly cited formulae based on laboratory data or field data were selected for validation using 180 laboratory data sets gathered from the literature and 446 field data sets collected from four countries. The six formulae validated in this paper are the Colorado State University (CSU), Neill, Froehlich, Breuser, Laursen, and simplified Chinese formulae. Comparisons between the predicted and measured depths were performed using scour from the laboratory and field data. An artificial neural network technique was also applied in order to compare the tendencies between the field and laboratory data sets. 相似文献
15.
Prediction of scour depth at piers with debris accumulation effects using linear genetic programming
Mehdi Jamei 《Marine Georesources & Geotechnology》2020,38(4):468-479
AbstractExact evaluation of scour depth around piers under debris accumulation is crucial for the safe design of pier structures. Experimental studies on scouring around pier bridges with debris accumulation have been conducted to estimate the maximum scour depth using various empirical relationships. However, due to the oversimplification of a complex process, the proposed relationships have not always been able to accurately predict the pier scour depth. This research proposes linear genetic programming (LGP) approach as an extension of the genetic programming to predict the scour depth around bridge piers. Among the artificial intelligence techniques, LGP and locally weighted linear regression (LWLR) models have not been used to predict the scour depth at bridge piers. Literature experimental data were collected and used to develop the models. The performance of the LGP method was compared with gene-expression programming, LWLR, multilinear regression and empirical equations using rigorous statistical criteria. The correlation coefficient (R) and the root mean squared error (RMSE) were (R?=?0.962, RMSE =0.31) and (R?=?0.885, RMSE =0.542) for the LGP and LWLR, respectively. The results demonstrated the superiority of the LGP method for increasing the accuracy of the predicted scour depth in comparison with the other models. 相似文献
16.
AbstractSediment 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
17.
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
18.
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