# 江湖汇流段桥墩布设对行洪安全的影响研究Study towards the Influence of Bridge Pier Layout on Flood Carrying Safety in River-Lake Confluence Section

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The confluence section of the Yangtze River and the Dongting Lake has always been a sensitive section for flood control, where schemes need to be adopted to calculate the impact of the project on flood dis-charge and river regime. In this paper, both mathematical and physical models are compared in analyz-ing the impact of the construction of a super-large bridge on river flood discharge in the confluence area of rivers and lakes. The results show that the construction has little effect on the water level and velocity of the main channel and the distribution pattern of cross-section velocity changes little, and the main flow line has not changed before and after the project. The comparison shows that the results between the two methods are not much different and the qualitative conclusions are consistent. There is no essential difference between the results obtained by the two methods, which can be used as the basic data for the analysis of Engineering impact degree and provide reference for design and river management.

1. 引言

2. 研究区概况

2.1. 河段概况

Figure 1. River trends of the engineering river section

2.2. 拟建工程概况

3. 模型构建与验证

3.1. 二维水流数学模型

1) 计算范围

2) 网格布置

3) 工程概化

3.2. 物理模型设计

1) 几何相似

2) 水流运动相似

3) 模型制作

Figure 2. Grid arrangement of computing area

3.3. 模型验证

3.3.1. 模型验证资料

3.3.2. 二维水流数学模型验证成果

3.3.3. 物理模型验证成果

Figure 3. Layout of model test section

Figure 4. Verification of water surface line

Figure 5. Verification of current velocity

4. 工程对河道行洪的影响分析

4.1. 模拟条件

Table 1. Calculation engineering conditions

4.2. 二维水流数学模型分析成果

4.2.1. 水位变化分析

4.2.2. 流速变化分析

1) 拟建工程的实施对对右岸的流速无影响；

2) 12#主墩两侧局部区域流速有所增加，其中右侧流速增加区域位于主槽内；

3) 左岸滩地上桥墩附近局部区域流速主要表现为减小。

4.2.3. 流向变化分析

4.3. 物理模型分析成果

4.3.1. 水位试验成果

4.3.2. 流速变化试验成果

1) 拟建工程的实施对流速的影响局限在工程附近的局部区域内，且对右岸的流速无影响，对左岸主槽流速的影响表现为Z12#主墩附近流速增加，其最大增加值为 0.05 m /s，最大流速增加区域在横向上距Z12#主墩约400 m。

2) 拟建工程的实施将导致滩地上流速的变化，其中桥位上游流速减小最大值为 0.15 m /s；桥墩之间流速增加最大值为 0.09 m /s；最大影响范围为桥址上游0.5 km、下游1.5 km。

3) Z12#主墩及锚碇前缘水流流速减小，其中距Z12#主墩前缘15 m处水流流速减小最大值为 0.14 m /s；距锚碇前缘15 m处水流流速减小最大值为 0.16 m /s。

4.3.3. 流向变化试验成果

4.4. 结果对比

5. 结论

1) 桥梁主桥采用双塔双跨钢桁架梁悬索桥，采取桥墩布设尽量减少数量、规避主泓区域的设计措施后，数学模型和物理模型结果均显示，工程建设对河道水位及流场改变不大，影响范围有限，不会对工程河段河道行洪产生明显不利影响。

Table 2. Water level changes before and after construction

Table 3. Comparison of physical model test and mathematical model calculation results

2) 两种方法取得的成果进行相互对比、校核，避免了一种方法可能存在的误差对评价结论带来的影响，两种方法取得成果无本质区别，均可以作为工程影响程度分析的基础数据。考虑到数学模型计算水位壅高值略小于物理模型，流速变化略大于物理模型计算成果，按照偏安全的原则，工程影响程度以计算中较大值作为评价工程建设影响的依据。

3) 为进一步减小工程建设对河道行洪的影响，建议加强河段内桥墩的尺寸和形状研究，尽量减小阻水面积，提升桥墩的流线型设计与河段内不同洪水流态的吻合度。

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