Investigation of Piping Erosion in Embankment Dams with Downstream Filters

This paper describes the experimental methods developed to understand the piping erosion of impervious core and its interaction with downstream filters in embankment dams. Concentrated leaks through a dam core-filter system are simulated experimentally in the hole erosion filter test (HEFT). The mass rate of erosion in the base soil, the eroded soils entrapped in the downstream filters, and the eroded soil particles passed through the filters that settled in the test unit and suspended in the effluent were derived throughout the test. An interpretation method of test results and determination of the rate of erosion of the dam core with downstream filters are proposed for which no methods are reported in the current literature. Results of experimental investigations indicated that the mechanism of erosion in a soil-filter system and the rate of erosion are influenced dominantly by the relative particle size distribution of base soils and filters, applied hydraulic gradient, coefficient of soil erosion, and dry density of base soil. For the soils and filters tested, the average erosion rate of a specimen compacted to 88% of the standard maximum dry density of soil compacted at standard optimum moisture content, Mdd, is about 4.1 times that of specimen with 97% Mdd. The average erosion rate for soil with erosion coefficient $1.54\times {10}^{-5}\mathrm{s}·{\mathrm{m}}^{-1}$ is about 15.4 times of that for soil with erosion coefficient $3.8\times {10}^{-6}\mathrm{s}·{\mathrm{m}}^{-1}$ for the same downstream filter and hydraulic gradient. The average erosion rate for a hydraulic gradient of 27.17 is about 2.2 times that for a hydraulic gradient 18.9 for the same soil and filter tested. Application of the HEFT for assessing the piping risk rating of embankment dams is presented.

The practical applications of the HEFT presented in this paper extend to the assessment of the piping risk rating of embankment dams. These findings provide a valuable foundation for improving dam safety protocols and the design and maintenance of embankment dams. By gaining a deeper understanding of the factors influencing piping erosion, dam engineers and geotechnical professionals can make informed decisions to enhance the resilience and safety of embankment dam structures, ultimately minimizing the risks associated with this critical geotechnical issue.