###### Abstract
For instance, at (just above) the \(w_{\rm P}\), silty, sandy, and peaty soils present slight toughness, whereas low-to-medium plasticity soils (e.g., silty clays) display medium toughness, with active clays exhibiting high toughness [11; 12; 13]. As stated on page 805 of the paper by [PERSON] [14], _\"the higher the position of a soil above the A-line on the plasticity chart (CL, CH), the stiffer are the soil threads near the plastic limit\"_. Hence, the concepts of plasticity and toughness could be considered synonymous from a practical standpoint. Note that another term often used to denote toughness is workability [8; 9; 13], perhaps of more importance for the ceramics and brick-making industries and in an agricultural context [8]. [PERSON] [1; 2] identified the water content range over which soil behaves in a plastic manner using the plasticity index \(I_{\rm P}\) (\(=w_{\rm L}-w_{\rm P}\)), where \(w_{\rm L}\) is the liquid limit water content. These index parameters are ubiquitously used for fine-grained soil classification, typically employing the Casagrande plasticity chart that plots \(I_{\rm P}\) against \(w_{\rm L}\), with the test soil classified as _clay_ or _silt_ material depending on its position relative to the A-line demarcation boundary in the \(I_{\rm P}\) versus \(w_{\rm L}\) plot [14; 15; 16]. However, the size of the water content range over which the soil behaves plastically (i.e., given by its \(I_{\rm P}\)) or the upper limit of that range (i.e., \(w_{\rm L}\)) are not, by themselves, satisfactory measures of soil toughness. In other words, soil toughness is a more fundamental plasticity property, typically quantified as the amount of work undertaken per unit soil volume necessary to change shape, remold, or, as in the case of the standard \(w_{\rm P}\) test, roll out uniform soil cylinders (threads) applying sufficient finger pressure during the repeated traverses [8; 17; 18]. The literature presents only a handful of cases employing empirical classifications of soil remolding toughness (these are based on qualitative or subjective assessments/descriptions of the observed soil behavior). A few cases reported in the literature purport to provide semi-quantitative assessments of soil toughness, and apparently, only one reported apparatus and test method [8; 17; 18] presently exists to provide direct toughness measurements. Neither has the property of soil remolding toughness been used that much in soil classification systems, with all of these points reflected by the sparsity of published work on the subject matter compared to, for instance, the voluminous reported work on the consistency limits (i.e., \(w_{\rm L}\) and \(w_{\rm P}\)) determination. This includes improved knowledge and understanding of the fall cone and Casagrande \(w_{\rm L}\)[19; 20; 21] and Afterberg \(w_{\rm P}\)[8; 17; 18; 22] state transitions and their experimental determination, methods of relating Casagrande cup and fall cone \(w_{\rm L}\) for a given fine-grained soil investigated [19; 23; 24], and various alternative proposals for soil plasticity (\(w_{\rm P}\)) determination, mostly based on fall cone approaches. The latter includes using a modified fall cone setup with an enhanced cone mass and incorporating a drop height [25; 26] (such that the falling cone hits the surface of the soil test specimen with an impact velocity) for the determination of the \"plastic strength limit\" \(PL_{100}\) parameter [19; 22; 27; 28] and various investigations of the fall cone flow curve for soil plasticity determination [29; 30]. Significant recent developments in fine-grained soil classification systems based on plasticity include the proposals of [PERSON] and [PERSON] [11; 31] and [PERSON] et al. [32]. [PERSON] and [PERSON] [11; 31] developed their proposal according to objective criteria based on the quantitative measurement of properties, such as soil toughness, the bending capacity of formed soil threads, and the observation of adhesive consistency, whereas the [PERSON] et al.