Laboratory Test for Evaluating Limitation of Flows during Internal Erosion in Zoned Dams

摘要

A new laboratory test, named the flow limitation erosion test (FLET), has been designed and developed to study upstream flow limitation during the phase of progression of internal erosion in the embankment of zoned dams. Upstream flow limitation may occur because of the presence of the shell or a transition zone upstream of a cracked core. In the FLET, the soil specimen is composed of core and upstream shell materials. These are compacted inside a test apparatus made up of several pieces assembled in steps. Then the soil specimen is subjected to water flow through a predrilled hole in the core material to simulate a concentrated leak, initiated, for example, by large differential settlement or hydraulic fracture. In most tests, the hole is also drilled in the upstream material to simulate the scenario in which the mechanism causing the flaw in the core is also likely to affect the upstream zone. Combinations of the same core material and several types of coarse-grained upstream materials (broadly graded and gap-graded soils) are tested for a range of compaction conditions and hydraulic loads. It is shown that FLET is capable of assessing whether there is upstream flow limitation and whether the internal erosion process stops, shows a trend of slowing down, or progresses. Upstream flow limitation is shown to be dependent on the fines and gravel content, fines plasticity, and compaction water content of the upstream material. In the particular case of the tested gap-graded soils, it is shown to be also dependent on the initial gradient along the upstream material.