Discussion of “Correlations for Fully Softened Shear Strength Parameters” by B. A. Castellanos, T. L., Brandon, and D. R. VandenBerge, This Article Was Published in Geotechnical Testing Journal , Vol. 39, No. 4, 2016. [DOI: 10.1520/GTJ20150184]

• Published in: Geotechnical testing journal 2017-05, Vol.40 (3), p.517-525
• Main Author: Stark, T. D.
• Format: Article
• Language: English
• ISSN: 0149-6115; 1945-7545
• DOI: 10.1520/GTJ20160148

In this paper, the authors criticize the fully softened strength (FSS) correlation by Stark and Eid (Stark, T. D. and Eid, H. T., 1997, “Slope Stability Analyses in Stiff Fissured Clays,” J. Geotech. Geoenviron. Eng., Vol. 123, No. 4, pp. 335–343) and subsequent updates (Stark, T.D., Choi, H., and McCone, S., 2005, “Shear Strengths for Analysis of Landslides,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 131, No. 5, pp. 575–588; Stark, T. D. and Hussain, M., 2010, “Shear Strength in Preexisting Landslides,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 136, No. 7, pp. 957–962; Gamez, J. and Stark, T. D., 2014, “Fully Softened Shear Strength at Low Stresses for Levee and Embankment Design,” Geotech. Geoenviron. J., Vol. 140, No. 9) in the following five areas: (1) use of a torsional ring shear device, (2) converting the ring shear results to the triaxial compression mode of shear, (3) sample processing, (4) a non- continuous strength envelope, and (5) use of three distinct clay-size fraction groups even though admitting that the Stark and Eid (Stark, T.D. and Eid, H.T., 1997, “Slope Stability Analyses in Stiff Fissured Clays,” J. Geotech. Geoenviron. Eng., Vol. 123, No. 4, pp. 335–343) correlation “is used widely and has been generally accepted in practice.” The authors also use questionable direct shear test data from Castellanos (2014, “Use and Measurement of Fully Softened Shear Strength,” Ph.D. dissertation, Virginia Tech, Blacksburg, VA, p. 805, https://www.dropbox.com/s/0k0ym51d8jdmn4v/Castellanos-FSS-Thesis-2014.pdf?dl=0.) to develop a fully softened strength correlation based on index properties, i.e., clay-size fraction (CF) and plasticity index (PI). The following paragraphs address these five criticisms, the questionable ring shear and direct shear testing presented in Castellanos (2014, “Use and Measurement of Fully Softened Shear Strength,” Ph.D. dissertation, Virginia Tech, Blacksburg, VA, p. 805, https://www.dropbox.com/s/0k0ym51d8jdmn4v/Castellanos-FSS-Thesis-2014.pdf?dl=0.), and the proposed FSS correlation.