Validity and reliability of the Krumbein-Sloss chart for the estimation of shape-dependent geomechanical properties in sands

The Krumbein-Sloss chart has widely been used as a conventional method with its simplicity and subjectivity in evaluating particle shape parameters. However, its applicability in estimating roundness and sphericity has not yet been validated. We perform a questionnaire study of four sand samples from 2D microscopic images to estimate shape parameters from the chart, and compare it with the theoretically computed values. The results of chart estimation show that the roundness and sphericity tend to be overestimated and underestimated than the computed values, respectively by questionnaires. By the chart-based estimation, we verified the regression model about shape parameters with index void ratio in previous literature, and also proposed a new regression equation to correlate the critical state friction angle. It indicates that the Krumbein-Sloss chart based estimation for quantifying the shape parameters shows statistically meaningful and can be used for correlating geomechanical property as well as predicting shape parameter.