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Title: Deriving parameters of a fundamental detachment model for cohesive soils from flume and jet erosion tests

Author
item AL-MADHHACHI, ADBUL-SAHIB - Oklahoma State University
item Hanson, Gregory
item FOX, GAREY - Oklahoma State University
item TYAGI, AVDHESH - Oklahoma State University
item BULUT, RIFAT - Oklahoma State University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2013
Publication Date: 4/1/2013
Citation: Al-Madhhachi, A., Hanson, G.J., Fox, G.A., Tyagi, A.K., Bulut, R. 2013. Deriving parameters of a fundamental detachment model for cohesive soils from flume and jet erosion tests. Transactions of the ASABE. 56(2):489-504.

Interpretive Summary: Determining the erodibility of cohesive soils is an important challenge for many water resource management issues in the world including levees, dams, dykes, rivers, streams, canals, and landscapes. The erosion rate of cohesive soils is commonly predicted based on the stress applied by the water flow and the erodibility of the soil. The erodibility of the soil is usually based on a threshold and rate coefficient parameter. A submerged jet test (JET – Jet Erosion Test) is one method that has been developed for measuring these parameters. This study proposes the use of an alternative model, "The Wilson Model," for predicting erosion rate. The advantage of this model is that it accounts for more soil properties and environmental conditions within the model. The objective of this study was to: 1) develop methods of analysis of the JET to measure the soil parameters for the "Wilson Model;" and 2) compare the previously measured parameters for predicting erosion rate to the "Wilson Model" parameters determined from the open channel laboratory tests and JET results for two cohesive soils. The open channel tests were treated as the standard test method, and JET tests were conducted on two soils to independently measure the soil parameters. There were two sizes of JET apparatus tested. The advantage to the "Wilson Model" is that it is a more mechanistically based detachment model and can be used to predict and account for the hydraulic stresses and soil material orientation across a larger set of environmental conditions.

Technical Abstract: The erosion rate of cohesive soils is commonly quantified using the 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. The disadvantage of using the excess shear stress equation is that parameters change according to erosion conditions. A more mechanistically based detachment model, the "Wilson Model," is proposed in this paper for modeling the erosion rate of soils for the range of environmental and fluvial conditions experienced. The general framework of the "Wilson Model" is based on two soil parameters (b0 and b1). The objective of this study was to: 1) develop methods of analysis of the JET to determine the b0 and b1 parameters from the "Wilson Model", in a similar fashion to the previous methodology developed for open channel flow; and 2) compare the excess stress parameter erodibility coefficient and the "Wilson Model" parameters b0 and b1 determined from the flume tests and JET test results for two cohesive soils. Flume tests, treated as the standard test method, and original and "mini" JET tests were conducted on two soils to independently measure the excess shear stress parameter erodibility coefficient, and the "Wilson Model" parameters b0 and b1. Soil samples of the two cohesive soils (silty sand and clayey sand soils) were placed and packed at different water contents in a soil box for the flume tests and the JET tests. No statistically significant differences were predicted for the excess shear stress parameter erodibility coefficient and for the "Wilson Model" parameters b0 and b1 when derived from the flume tests and JET devices, except for b1 with the original JET. The advantage of the "Wilson Model" is that the more mechanistically based detachment model can be used to predict and account for the hydraulic stresses and material orientation (i.e. stream beds versus streambanks).