Repeatability and agreement between methods for determining the Atterberg limits of fine‐grained soils

Abstract

The Atterberg limits (plastic limit [PL] and liquid limit [LL]) of fine‐grained soils are important for civil engineering and agronomic applications. Several methodologies exist to determine the PL and LL, each with associated merits and shortcomings. The reproducibility and uncertainties associated with the various methods have not been evaluated for different samples that differ in terms of clay mineralogy and geologic origin. The objectives were to (i) assess the repeatability of two methods each for determining the PL (thread rolling and rolling device) and LL (Casagrande cup and drop cone penetrometer), and compare the subsequent plasticity indexes for 30 samples from 10 countries; and (ii) evaluate the effect of particle size (2 mm and 425 µm) on the plastic and liquid limits for 28 Venezuelan samples. For the PL, the repeatability (estimated as the repeatability coefficient, RC, among replications) for the thread rolling and rolling device methods was similar (2.28 and 2.39%, respectively). For the LL, the drop cone method was 16% more repeatable than the Casagrande cup method. There was a strong correlation between the two respective methods for PL (r2 = 0.98) and LL (r2 = 0.99). For samples that have LL < 45, the LL from the Casagrande cup was slightly higher than LL from the drop cone, and vice versa for samples with LL > 45%. No significant differences were observed between PL measured on <2‐mm or <425‐µm samples; for samples with LL < 35% the two particle sizes gave similar values. There were however larger discrepancies between the two particle sizes for samples with LL > 36%.

Review of Recent Developments and Understanding of Atterberg Limits Determinations

“…The Bobrowski and Griekspoor [44] test method utilizes a rolling device comprising two acrylic flat plates covered with unglazed paper, downward force being simultaneously applied (via the top plate) to the soil thread with the back and forth rolling motion, until the top plate comes into contact with 3.2 mm-deep side rails. Despite Bobrowski and Griekspoor [44] claiming that PLs are obtained in a more expeditious and uniform fashion, their experimental findings along with those of Rashid et al [51], Ishaque et al [52] and Rehman et al [53] independently indicated that the water contents for the thread crumbling condition obtained using this plate rolling device (i.e., PL PRD ) generally underestimate their PL HR values. It has been suggested that this most likely occurred because the paper attached to the flat plates tends to produce inhomogeneity of the soil thread, the outside becoming drier than its core, during the rolling out procedure [13].…”

“…Ishaque et al [52] also reported that this method is not a workable means for 'non-cohesive' (i.e., silt) soils. However, given the relatively small number of fine-grained soils examined in each of the Bobrowski and Griekspoor [44], Rashid et al [51], Ishaque et al [52] and Rehman et al [53] studies, the author of this paper believes it would be worth revisiting, and judging the PL PRD reliability/repeatability, with respect to the PL HR , based on statistical analysis of these combined PL PRD datasets.…”

Reappraisal of the ASTM/AASHTO Standard Rolling Device Method for Plastic Limit Determination of Fine-Grained Soils

“…A detailed description of the assembled database is presented in Table 1. The database consisted of 51 PL RT -PL BG data pairs sourced from the research literature (designated by Test IDs S1-S51) [52,[63][64][65], as well as original test results of nine fine-grained soils investigated by the authors (Test IDs S52-S60). As demonstrated in Table 1, the database soils, in addition to their geographical diversity, cover reasonably wide ranges of surface texture, plasticity and mineralogical properties-that is, f clay (<2 µm) = 8.9-59.5%, f silt (2-75 µm) = 7.0-72.7%, LL FC = 24.6-141.1%, PL RT = 11.9-53.4%, PI FC-RT = LL FC − PL RT = 8.1-101.6%, and A FC = PI FC-RT /f clay = 0.49-1.85 (where f clay , f silt , LL FC , PL RT , PI FC-RT and A FC denote clay content, silt content, BS fall-cone liquid limit, standard rolling-thread plastic limit, plasticity index deduced from the FC and RT test results, and soil activity index, respectively).…”

“…Following the BA framework, the 95% lower and upper agreement limits between the PL BG and PL RT can be, respectively, defined as LAL = µ D − 1.96 σ D and UAL = µ D + 1.96 σ D (where µ D and σ D denote the arithmetic mean and standard deviation of the D BA = PL BG − PL RT data, respectively). Note that the calculated LAL and UAL must be examined against an inductively-defined limit, often selected as the highest possible (water content) difference/variation in the standard measurement method (i.e., PL RT ) based on its repeatability [65]. A review of the research literature indicates that the maximum variation in the PL RT for a given fine-grained soil (accounting for measurement variations across multiple operators) can be conservatively taken as ±8% [34].…”

Quantifying Cereal Productivity on Sandy Soil in Response to Some Soil-Improving Cropping Systems

“…The Bland-Altman method is widely used in medicine (e.g., [42][43][44]) and in some satellite research [45,46]. More recent studies showed usefulness of this approach to quantify pure effects of agricultural practices on crop yield and soil physical properties [47,48] and the agreement between methods for determining the Atterberg plastic and liquid limits of soils [49]. This study was inspired by recent literature reviews indicating that, despite their importance, sandy soils have received less research attention compared to other soils [1,5].…”