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Tony L. Wahl, Pierre-Louis Regazzoni, and Zeynep Erdogan. 2009. "Practical Improvements for the Hole Erosion Test". Bureau of Reclamation, Report Number PAP-994.

Abstract: The constant-head hole erosion test (HET) is one of several available procedures for characterizing the erodibility of cohesive soils important to internal erosion investigations of dams and levees. Measurements of accelerating flow rate through an eroding pre-drilled hole in a test specimen yield estimates of the critical shear stress and erosion rate coefficient. Two methods for analyzing HET data were investigated. The first is a deterministic method in which initial and final eroded hole diameters are used to compute initial and final friction factors, and intermediate hole diameters are then computed from flow rates measured during the course of the test. The variation of the friction factor during HETs was studied and an improved modeling method was developed for estimating intermediate values of the friction factor. The second method for HET data analysis is the fitting of the observed flow rate record to a nondimensional numerical model for piping erosion. This method does not require determination of friction factors nor the measurement of the final hole diameter, which can be problematic. Applying both analysis methods to numerous tests showed that they yield generally similar results. As a result, the Bureau of Reclamation has drafted new procedures for performing HETs and analyzing test data. Unfortunately, tests do not always proceed as planned, so both analysis methods are not applicable to all tests. Thus, Reclamation uses each analysis method as appropriate, based on judgment of the analyst. This increases the rate of test success, although there are still some tests that defy analysis. The applicability of the HET to soils of varying erodibility is discussed and compared to other erodibility test methods.

Web Link: http://www.usbr.gov/pmts/hydraulics_lab/pubs/PAP/PAP-0994.pdf

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