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United States Department of Agriculture

Agricultural Research Service

Research Project: ENGINEERING TOOLS FOR SAFE, EFFICIENT HYDRAULIC STRUCTURES AND CHANNELS

Location: Hydraulic Engineering Research

Title: Measuring soil erodibility using a laboratory "mini" JET

Authors
item Al-Madhhachi, Abdul -
item Hanson, Gregory
item Fox, Garey -
item Tyagi, Avdhesh -
item Bulut, Rifat -

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2013
Publication Date: June 1, 2013
Citation: Al-Madhhachi, A.T., Hanson, G.J., Fox, G.A., Tyagi, A.K., Bulut, R. 2013. Measuring soil erodibility using a laboratory "mini" JET. Transactions of the ASABE. 56(3):901-910.

Interpretive Summary: Erosion of soil materials occurs in many water flow environments such as rivers, streams, levees, dams, etc. A submerged jet erosion test (JET) is one method that has been developed for measuring the erosion resistance or more commonly termed "erodibility" of soil materials to predict how they will perform in water flow environments. This study compares measurement results from a smaller version of the JET device, referred to as the "mini" JET. Comparisons are made by conducting side by side laboratory tests of equivalently prepared soil samples. The JET test measures two parameters to determine erodibility. The two parameters are the erodibility coefficient and the critical stress. The erodibility coefficient results compared very well between the original JET and the "mini" jet. It was determined from the test results that an adjustment factor would need to be applied to the "mini" JET results for the critical stress values to agree with the original JET device. It was determined that with proper accounting and understanding of the results the "mini" JET can be used instead of the original JET apparatus for characterizing the erodibility of soil materials. The "mini" JET device will be more convenient to use in more remote environments or in situations where water supply is a limiting factor.

Technical Abstract: Typically the erosion rate of cohesive soils is quantified using an excess shear stress equation, dependent on two major soil parameters: the critical shear stress and the erodibility coefficient. A submerged jet test (JET – Jet Erosion Test) is one method that has been developed for measuring these parameters. In this study, a new miniature version of the device ("mini" JET), with the advantage of being easier to use in the field, was used to measure critical shear stress and erodibility coefficient for two cohesive soils (silty sand and clayey sand) and results were compared to the larger original laboratory JET. The objective of this research was to determine if the "mini" JET measured equivalent values for critical shear stress and erodibility coefficient compared to the original JET device. Samples of the soils tested were prepared at different water contents with a standard compaction effort of 600 kN-m/m**3 (ASTM). In-order to compare the performance and repeatability of both JET devices, tests were performed on paired samples prepared in the same way and tested at the same time. Some variability in measuring critical shear stress and erodibility coefficient was observed between paired samples due to variability in the subsamples of the cohesive soil and differences in soil moisture levels. Reasonably equivalent erodibility coefficient values were measured by the two JET devices for both soils but the critical shear stress values measured by the "mini" JET were consistently lower. Observations during testing indicated that settling back of some of the eroded soil into the scour area of the new "mini" JET device may have caused differences in the measured critical shear stress relative to the original JET device. Adjustment of the ratio of the equilibrium depth to the nozzle height of the "mini" JET in the analysis resulted in minimal differences in the estimated critical shear stress between both JET devices. Statistical tests indicated no significant differences between the devices for measuring critical shear stress and erodibility coefficient except for the pre-adjusted critical shear stress. Both JET devices also demonstrated consistent performance in measuring critical shear stress-erodibility coefficient relationships, which compared reasonably well with those observed in previous field research.

Last Modified: 4/17/2014