- Title
- Reappraisal of fall-cone flow curve for soil plasticity determinations
- Creator
- Soltani, Amin; O'Kelly, Brendan
- Date
- 2022
- Type
- Text; Journal article
- Identifier
- http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/184727
- Identifier
- vital:16582
- Identifier
-
https://doi.org/10.1520/GTJ20200312
- Identifier
- ISBN:0149-6115 (ISSN)
- Abstract
- Several attempts have been made to devise alternate plastic limit (PL) determination methods, targeting higher degrees of repeatability and reproducibility. Among these, empirical-type correlations linking the plasticity index (PI) to the flow index (FI) - the slope magnitude of the flow curve - seem to be gaining increased attention, particularly for the fall-cone (FC) approach, and hence demand further examination. To better understand the true potentials and limitations of this emerging practice for soil plasticity determination, this study presents a critical statistical appraisal of FI-based correlations - using a large and diverse database of 230 FC tests (for the 80 g-30° cone) - in estimating the PI (and hence the PL). It is demonstrated that the so-called "strong"correlation between the PI and FI reported in some literature, favoring the use of FI as a PI estimator, is an overlooked "statistical pitfall"originating from an over-reliance on the coefficient of determination (R2) statistic. Employing appropriate error-related statistics, it is shown that the PI predictions made by FI-based correlations are associated with high average errors of 22-33 %. Hence, such correlations, at best, can only provide a rough approximation of the actual PI (and hence PL). An attempt is also made to assess the validity of FI-based correlations in the context of soil classification using the Casagrande-style plasticity chart. The agreement level between the conventional classification approach and that performed using PI deduced from FI-based correlations was 75-80 %. This analysis, however, did not account for errors in the rolling-thread plastic limit data, maintaining a strong possibility that FI-based correlations may be suitable for routine soil classification purposes. © 2021 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
- Publisher
- ASTM International
- Relation
- Geotechnical Testing Journal Vol. 45, no. 1 (2022), p.
- Rights
- All metadata describing materials held in, or linked to, the repository is freely available under a CC0 licence
- Rights
- Copyright © 2021 ASTM International
- Subject
- 4005 Civil Engineering; 4019 Resources Engineering and Extractive Metallurgy; Fall-cone flow curve; Flow index; Plastic limit; Plasticity index; Soil classification
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