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Title: EROSION FUNCTION APPARATUS FOR SCOUR RATE PREDICTIONS: DISCUSSION

Author
item Hanson, Gregory
item Simon, Andrew

Submitted to: Journal of Geotechnical and Geoenvironmental Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2002
Publication Date: 7/1/2002
Citation: Hanson, G.J., Simon, A. 2002. Erosion function apparatus for scour rate predictions: Discussion. Journal of Geotechnical and Geoenvironmental Engineering. 127(2):105-113.

Interpretive Summary: This paper discusses a paper of "Erosion Function Apparatus for Scour Rate Predictions" written by J.L. Briaud, H.C. Chen, Y. Cao, W. Han, and K. W. Kwak and published in the Journal of Geotechnical and Geoenvironmental Engineering Vol. 127, No. 2 pp. 105-113, 2001. Briaud et al. point out the need for a tool to measure the erosion resistance of soil materials in streambeds around bridges because bridge scour is the number one cause of bridge failures. Briaud et al. describe a tool that they have developed to measure erosion resistance. This discussion paper supports the need pointed out by Briaud et al. as well as points out the development of a submerged jet apparatus that can be used for the same purpose. The submerged jet apparatus can be taken to the field to conduct measurements rather than bringing a sample into the laboratory as required by the apparatus described by Briaud et al. Submerged jet test results of cohesive streambeds are also compared with the results of Briaud et al. The results show similar trends and indicate that the samples tested by Briaud et al. classify as very erodible to moderately erodible in the five-category classification system developed from submerged jet test results. Measurement of cohesive soil material erosion resistance is important for designing bridges as well as many other engineered structures built in and around water. Being aware of the tools available to the engineer for this purpose is essential to proper design.

Technical Abstract: This paper is a discussion paper of "Erosion Function Apparatus for Scour Rate Predictions" written by J. L. Briaud, H.C. Chen, Y. Cao, W. Han, and K. W. Kwak and published in the Journal of Geotechnical and Geoenvironmental Engineering Vol. 127, No. 2 pp. 105-113, 2001. Scour is the number one cause of bridge failures, and Briaud et al. developed an erosion apparatus for characterizing streambed materials. The apparatus is used to measure both the erosion rate with changes in hydraulic stress. The apparatus requires an undisturbed sample brought into the laboratory. Briaud et al. defined two terms based on their test result: the initial slope of the erosion rate curve Si, and the critical stress ?c. The results and purpose of this apparatus are similar to the submerged jet apparatus for characterizing the erodibility of cohesive materials. The results of the jet apparatus are used to determine the erodibility coefficient kd, and d?c. These terms are very similar in definition to the terms defined by Briaud et al. The results of tests on cohesive stream beds using the jet apparatus are compared with the results by Briaud et al. The results indicate that the erodibility the soil materials tested by Briaud et al. have similar trends and classify as very erodible to moderately resistant. The discussion paper lends support to the conclusions about cohesive soil erodibility testing as described by Briaud et al. It also points out the option of in-situ testing of cohesive materials using a submerged jet apparatus.