Discussion: Influence of external stress and initial density on the volumetric behavior of an expansive clay during wett
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Discussion: Influence of external stress and initial density on the volumetric behavior of an expansive clay during wetting [Environ Earth Sci (2020) 79(10), 211] Amin Soltani1 Received: 22 August 2020 / Accepted: 14 October 2020 / Published online: 31 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Keywords Expansive clay · Swelling and collapse · Primary swelling/collapse coefficient · Secondary swelling/collapse coefficient · Subjective variability
Introduction Recently, Zou et al. (2020) investigated the evolution of wetting-induced strain (both swelling and collapse) with respect to time over a wide range of initial placement conditions and vertical stress levels for an expansive soil sample collected from Nanyang, China. The swell/collapse–time plots were analyzed by means of a four-parameter dose–response fitting model (i.e., Eq. 2 in the original manuscript), and the swell/collapse–time characteristics—that is, the completion times of the initial and primary swelling/collapse stages (and hence the primary and secondary swelling/collapse coefficients)—were calculated using a so-called “graphical construction”. The work under discussion is a welcome addition to the research literature, and the discusser would like to commend the authors for their valuable work. This discussion piece aims at addressing some apparent shortcomings and limitations associated with the data analyses and interpretation for the Zou et al. (2020) investigation, as well as complementing the original work by outlining a novel point of view. The discusser would like to draw the authors’ attention to the following critical points: • Inconsistencies with the standard graphical construction
The standard graphical construction for determining the initial and primary swelling/collapse margins, as outlined in ASTM D4546 (2014) and commonly practiced in the research literature (e.g., Sridharan and
* Amin Soltani [email protected] 1
School of Engineering, IT and Physical Sciences, Federation University, Churchill, VIC 3842, Australia
Gurtug 2004; Nagaraj et al. 2010; Ye et al. 2015; Chen et al. 2016; Belchior et al. 2017; Soltani et al. 2017, 2018a, b, 2019), is illustrated in Fig. 1. As demonstrated in the figure, the standard graphical method involves locating the curve’s inflection point by way of visual observation, i.e., Point O, and manually extending three inclined tangents, namely ISL (at Point I), PSL (at Point O) and SSL (at Point S). The intersections of these three tangents are then defined as the initial and primary swelling/collapse margins (i.e., Points A and B on the curve). The abscissas of these intersections represent the completion times of the initial and primary swelling/collapse stages, i.e., ti and tp, which are used to mathematically quantify the coefficients of primary and secondary swelling/collapse by means of Eqs. 4 and 5 presented in the original manuscript. The graphical construction introduced by the authors, which is also shown in Fig. 1, clearly differs
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