Laboratory Test for Evaluating Crack Filling During Internal Erosion in Zoned Dams

A new laboratory test, the crack-filling erosion test (CFET), was developed to study crack filling during the progression of internal erosion in the embankment of zoned dams. Crack filling involves the transport of eroded material from an upstream zone, through a flaw in the core, which is then retained by a downstream granular layer. In the CFET, the specimen comprises a core, an upstream shell material, and a downstream filter layer. These are compacted inside a test apparatus made up of several pieces. The specimen is subjected to water flow through a predrilled hole in the core to simulate a concentrated leak. Seven granular upstream materials, two core soils, and two granular filters are examined. Following an extensive testing program, experimental observations and physical descriptions are presented. Three main types of pattern behaviors are identified: rapid crack filling with almost “no erosion” of the core; filtering after “some erosion” or “excessive erosion” of the core and/or upstream material; and “continuing erosion” of the core and upstream material. When the core has moderate-to-high resistance to erosion, crack filling is mainly governed by grading properties of the upstream zone and of the filter. Crack filling is more likely to occur the finer the filter layer, the higher the fine-sand content of the upstream soil, and the lower the fines content of the upstream soil. Test results are checked against the subjective guidelines on crack-filling action available in the literature.