钱塘江河口过江隧道河段极端洪水冲刷深度的预测

Prediction of erosion depth under the action of the exceptional flood in the river reach of a tunnel across the Qiantang estuary

钱塘江河口为强冲积性河口,在洪潮水流共同作用下河床冲淤剧烈,极端洪水条件下河床的冲刷深度是过江隧道工程的关键问题之一。基于河床演变分析、动床数值模拟和动床物理模型等研究手段,建立了钱塘江河口过江隧道河段洪水冲刷深度的预测模型,分别经钱塘江河口的典型实测地形、水流泥沙及河床冲淤等实测资料进行验证。在此基础上预测了某过江隧道河段在极端洪水作用下河床最大冲刷深度,三种研究方法所得的结果定性定量基本合理,且与后来地质详勘的沉积分析成果基本一致,进一步表明了预测模型的可靠性,预测的最大冲刷深度可为过江隧道的合理埋设提供科学依据。

The Qiantang estuary is a strong alluvial estuary. The sedimentation/erosion extends usually reaches 5 - 10 under the action of the flood or tidal flow. So the riverbed erosion extend is the key technical problem for the tunnel project across the Qiantang estuary. In the paper, three prediction methods on the maximum erosion depth of the river bed nearby this tunnel are set up based on the analysis of the hydraulic geometry of river channel, the sediment mathematical model and the movable bed physical model. These models are calibrated using hydrographic field data as well as those on the historical morphological changes in the Qiantang estuary. After the calibration these models are used to investigate the maximum scour depth caused by an exceptional flood in the cross-section of a tunnel across the Qiantang estuary. Finally, the maximum erosion depth and ero- sion curve of the riverbed cross-section nearby the tunnel under the 100-year flood is predicted by the three predicting methods, and the predicted result agrees very well with the geologic drilling data. It is shown that the predicted result is basically reasonable and the scientific basis is offered for the study of this tunnel.