承受长周期船行波越顶荷载的抛石丁坝设计方法

摘要

近年来，随着船队结构逐步向大型船舶演变，德国河口地区的船行荷载持续增大。其中丁坝尤易受长周期初级船行波荷载的影响：波浪越顶丁坝的现象在部分河段已造成严重破坏。近年来的研究多集中于水动力过程本身，而针对这一特殊荷载工况的抛石粒径设计方法迄今仍属空白。为建立设计方法并深入认识导致丁坝冲刷的过程，本文对既有的两座丁坝原型试验数据进行了分析。该原型试验历时数年，配套开展了包括波浪与流速观测以及激光扫描测量在内的综合监测。文中考察了初级波高、越顶水流条件与石块运动之间的关系，并利用其与堰流及抛石护坡越流问题的相似性，将既有解析公式与经验公式应用于本问题并加以评价，同时讨论了周围水位等重要影响因素。最终，采用 Thornton 等提出的稳定性函数可正确预测绝大多数实测冲刷事件，且误判事件极少。在此基础上，本文提出了承受长周期船行波荷载的抛石丁坝粒径设计流程。

Abstract

In German estuaries ship-induced loads have increased in recent years due to the gradual change of the fleet structure towards bigger vessels. Groynes in particular are vulnerable to long-period primary ship wave loading due to an overtopping phenomenon which at some localities leads to severe damages. While in recent years the hydraulic processes have been the focus of investigations, currently no rock sizing method exists for this special load case. To develop a design method and to better understand the processes leading to groyne erosion, the data from a previously conducted prototype experiment with two groynes is analysed in this paper. The prototype experiment was carried out over several years and was accompanied by a comprehensive monitoring, consisting of wave and current measurements as well as laser scan surveys. Relationships of primary wave heights, overtopping flow conditions and rock movements are investigated. Making use of similarities to weir flow and overtopped riprap embankments, existing analytical and empirical formulae are applied to this problem and evaluated. Important influencing factors like the ambient water level are discussed. Ultimately, using the Thornton et al. (2014) stability function the majority of observed erosion events could be predicted correctly with only a small number of false detects. On this basis, a workflow for the stone sizing of rock groynes exposed to long-period ship waves is formulated.