Abstract

A major hazard to embankment dams is internal erosion and piping arising from concentrated leaks through transverse cracks in the core near the crest due to differential settlement or desiccation. This contribution summarises experiments and a formal boundary layer analysis of flow through such transverse cracks subject to near-horizontal pressure gradients. The critical hydraulic gradients, at which erosion in such cracks may initiate, occur at the downstream end of the crack. This location and the maximum crack width defines the local point most vulnerable to erosion. The hydraulic laboratory measurements are shown to be consistent with equivalent international standards describing depths at free overflows, in spite of the narrow vertical profile of the cracks, provided that the tendency towards laminar flow in very narrow cracks is incorporated within the modelling. A backwater model based on conventional representations of flow in narrow channels is verified qualitatively by hydraulic laboratory data. Flow-depth relationships, maximum crack wall hydraulic stresses, normalised hydraulic wall stress profiles and depth profiles along cracks are presented for the two principal crack geometries present in embankment dams. These characterisations are a significant improvement on the simplified methods previously used to assess internal erosion in transverse cracks in dams.

摘要

堤坝的一个主要危险是内部侵蚀和管道，这是由于不均匀沉降或干燥造成的，通过坝顶附近核心区的横向裂缝集中泄漏。这一贡献总结了实验和正式的边界层分析，分析了在近水平压力梯度下通过这种横向裂缝的流动。临界水力梯度，在这种裂缝中可能开始侵蚀，发生在裂缝的下游端。这个位置和最大裂缝宽度定义了最容易受到侵蚀的局部点。尽管裂缝的垂直剖面很窄，但水力实验室测量结果表明与描述自由溢流深度的等效国际标准一致，前提是模型中包含了非常窄的裂缝中的层流趋势。水力实验室数据对基于狭窄渠道流动常规表示的回水模型进行了定性验证。针对路堤坝中存在的两种主要裂缝几何形状，提供了流动深度关系、最大裂缝壁水力应力、归一化水力壁应力分布和沿裂缝的深度分布。这些特征是对以前用于评估大坝横向裂缝内部侵蚀的简化方法的重大改进。给出了堤坝中存在的两种主要裂缝几何形状的归一化水力壁应力分布和沿裂缝的深度分布。这些特征是对以前用于评估大坝横向裂缝内部侵蚀的简化方法的重大改进。给出了堤坝中存在的两种主要裂缝几何形状的归一化水力壁应力分布和沿裂缝的深度分布。这些特征是对以前用于评估大坝横向裂缝内部侵蚀的简化方法的重大改进。