Determining Erosion Indices of Cohesive Soils with the Hole Erosion Test and Jet Erosion Test

Two methods of soil erodibility testing, the hole erosion test (HET) and submerged jet erosion test (JET), were investigated to determine the correlation between their results and to evaluate and improve them for potential application to the modeling of embankment dam erosion and breach processes. Basic assumptions regarding the behavior of the friction factor for flow through the predrilled hole in the HET were investigated, and it was found that the friction factor was best correlated with the hole diameter rather than the test time as previous investigators had assumed. This finding and others were used to develop improved HET testing and data analysis procedures including a method that does not require measurement of the final eroded hole diameter. The HET and JET methods were compared to one another by using them to determine erodibility parameters of identically prepared remolded soil specimens. The JET method indicated much greater erodibility in a direct comparison of quantitative results, which indicates that results of each test should be interpreted using criteria adapted to each particular test. Differences in erodibility were one or more orders of magnitude in erosion rate and two or more orders of magnitude in critical shear stress. The JET method seemed to be more sensitive to variations in soil fabric, and specimens with a coarse and nonuniform soil structure seemed to produce the greatest differences between HET and JET results. Differences between HET and JET results are also thought to include simplified stress descriptions in each test environment and fundamental differences in the mechanisms of erosion exploited by each test. The JET proved to be a more easily applied test method, with a higher ratio of successful tests and a greater ability to successfully test soils of widely varying erodibility. The JET also has the advantage of being suitable for in situ field testing wherever a soil surface of interest can be exposed. Ultimately, selection of a test for any particular purpose should be made primarily based on the application and the erosion mechanisms of importance.