Discussion: Development of a Single-Point Method to Determine Soil Plastic Limit Using Fall-Cone Data [Geotech Geol Eng 41:4473–4485, 2023]

This discussion article presents a critical appraisal of three empirical correlations developed via multiple regression analysis and presented in the Kayabali et al. [Geotech Geol Eng 41:4473–4485, 2023. https://doi.org/10.1007/s10706-023-02527-0 ] (the Authors’) investigation for the determination of the soil consistency limits. Specifically, based solely on British Standard (BS) fall-cone (FC) test data, the Authors purport that the correlations given by Equations 2 and 3 of their paper can be used to predict the ASTM rolling-plate plastic limit (i.e., PL RP ), while their Equation 4 can be used to predict the BS FC liquid limit (i.e., LL FC ). The Authors demonstrated that these correlations gave good predictions of the measured LL FC and PL RP water contents (i.e., w L(FC) and w P(RP) , respectively) for 87 fine-grained soils they sourced from different parts of Central Turkey. Employing newly compiled large and diverse consistency limits databases assembled from the published research literature, this discussion article confirms that the Authors’ Equations 2 and 3 generally produce poor w P(RP) predictions for the fine-grained soils comprising these databases, invariably overestimating (often seriously) their measured plastic limit values. Hence, the Discussers recommend that the Authors’ Equations 2 and 3 (being generally unreliable beyond the investigated Turkish soils) should not be used in geotechnical engineering practice. While the Authors’ single-point LL FC method given by their Equation 4 broadly appears as a good w L(FC) predictor for the newly compiled database soils, it is noted that there already exist well-established and standardised single-point LL FC methods.