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Settlement of structures is determined by the stiffness of the soil where they are built. Compression index (c c) quantifies the compressibility of the soil and is a key parameter in the design of geotechnical structures. To predict the value of c c in clay soils, a global database of more than 1000 data points was collected and analysed. Liquid limit, plasticity index, natural water content, and initial void ratio were considered as predictor variables. A super-learner machine learning model was developed to predict c c from these variables. The model demonstrated a reasonable predictive performance and was subsequently integrated into an online tool. Additionally, four symbolic regression expressions were obtained to relate c c with some of the input variables when not all data are available, providing simple and practical alternatives for c c , estimation. This study provided two major contributions: (1) the non-local nature of the data expands the scope and generalizability of the findings, and (2) the availability of the proposed algorithm through an online application ensures its accessibility for geotechnical engineers, enhancing the work's practical applicability and intrinsic value. • Prediction of compression index from liquid limit, plasticity index, water content and void ratio. • Over 1000 data points worldwide were collected to predict compression index value in clays. • Optimized ensemble of three ML models offers reliable compression index estimates. • The online tool developed aids engineers in estimating the compression index from soil parameters. • Symbolic regression expressions are proposed for use when full data is unavailable. [ABSTRACT FROM AUTHOR]

Clays are key elements not only in geological and environmental processes, but also in many human activities. To differentiate clays from other soils, AIPEA and CMS highlight plasticity as the clays' most distinctive characteristic. However, the lack of any reliable plasticity yardstick makes the particle-size-criteria to be more widespread. In a previous work, the authors found some innovative ratios between the plasticity index (PI) and the liquid limit (LL) which allowed the clays' boundary to be established according to a plasticity basis. As plasticity is directly associated with toughness, different published data containing valuable information have been processed in this study by plotting toughness values against PI/LL ratios. In this way, the soundness of the previous authors' finding has been checked. It is demonstrated that a fine-grained material can be defined as a clay when PI ≥ LL/2, while a material is moderately or slightly clayey if LL/3 < PI < LL/2, such that when PI ≤ LL/3 the influence of clay minerals is much reduced. Apart from an updated classification of soil for engineering purposes, a new textural soil classification is presented, alternative to the USDA one, which allows the real nature of a soil to be known accurately by means of plasticity tests and simple sieving instead of particle-size sedimentation methods. [ABSTRACT FROM AUTHOR]

Among the multitude of alternate plasticity index (PI) estimation proposals, empirical correlations based on the linear shrinkage (LS) test, originally proposed in the 1967 edition of the British BS 1377 standard, seem to be gaining increased attention. This study has two main aims: (i) re-examining LS-based correlations for PI estimation to better understand their true potentials and/or limitations; and (ii) investigating the possibility of employing LS, as a proxy for the standard PI, for fine-grained soil classification. To this end, comprehensive statistical analyses were performed on the largest and most diverse database assembled of its kind, entailing PI:LS measurements for 265 different fine-grained soils [pertaining to the 'soft' base percussion-cup liquid limit (LL = 17–134%) and the Australian standard LS = 0.5–32.0%]. It was demonstrated that the LS can generally only provide a rough approximation of the actual PI. At best, only those predictions produced by PI = 1.86 × LS for low-plasticity soils (i.e., LL ≤ 35%) included in the database may be deemed acceptable, specifically when difficulties are encountered in executing the standard plastic limit (PL) thread-rolling test for such soils. The second/novel aim of this study found that the agreement level between the Casagrande-style plasticity-chart classification (based on the measured PI = LL − PL) and that performed using the PI deduced from a newly introduced multivariable correlation involving LS and LL, as inputs, was obtained as 95%. Hence, in the absence of measured PI, the multivariable PI:LS:LL correlation may be deemed suitable for preliminary soil classification purposes. • Examine linear shrinkage (LS) – liquid limit (LL) correlations for plasticity index (PI) estimates. • Statistical analysis of large PI:LS database for 265 different fine-grained soils with measured PL. • LS can generally only provide guesstimate of actual PI [= LL − thread-rolling plastic limit (PL)]. • For low-plasticity soils (i.e., LL ≤ 35%), predictions by PI = 1.86 × LS may be deemed acceptable. • New multivariable PI:LS:LL correlation deemed suitable for preliminary soil classification purposes. [ABSTRACT FROM AUTHOR]

Previous studies have used the clay content of soils for estimating the specific surface areas and different correlations have been found, including plasticity-value correlations. Based on several assumptions, Dolinar (2012) proposed a simplified method for determining the external specific surface area of non-swelling fine-grained soils. An equation relates the external specific surface area (BET-nitrogen) with percentage of clay fraction (< 2 μm), determined by hydrometer method, and plasticity index (Atterberg). In this work, based on that simplified method, the authors have developed an improved method for determining the external specific surface area of fine-grained clay samples. Instead of percentage of clay fraction, it was proposed to use the clay mineral content estimated by XRD methods. From an analysis of previous Dolinars results, the calculated and measured values of external specific surface area were studied for a group of non-swelling and fine-grained soil samples (Dolinar's samples), five non-swelling clayey samples and data samples from the literature. Additionally, an estimation of the plasticity index (Atterberg) has been also considered in this improved method. Both these methods, simplified and improved, were tested and compared using all these samples. It demonstrated the practical application of both these methods for an estimation of external specific surface area and plasticity index. However, in the present research two models were considered to determine the specific surface areas (BET and Langmuir) and the influence of several sources of errors in these predictions was discussed. The predictions were found more accurate when specific surface area from Langmuir's model is considered. It is concluded that the present research will be useful for the prediction of external specific surface area and plasticity index of non-swelling clayey materials and to dispose of theoretical practical relationships between clay mineralogy and geotechnical properties of valuable interest. [ABSTRACT FROM AUTHOR]

Abstract: The physical and mechanical properties of fine-grained soils, especially clay minerals, are greatly influenced by the specific surface area. Many investigations were conducted to examine the relationships between the specific surface area of soils and their engineering properties. We have previously shown that there were relationships between the external specific surface area of the soils and their Atterberg limits. These relationships, based on the test results from soils prepared artificially in the laboratory, were presented in a general analytical form. As Atterberg limits are the most distinctive and the easiest property of soils to measure, it would be a very convenient basis for estimating the specific surface area. The aim of these investigations was to identify the possibility of practical applications. Five heterogeneous soil samples were selected, the liquid and plastic limits were measured as well as the grain size distribution, the mineral and chemical compositions and the specific surface area. The external specific surface area of the soils measured by the BET method ranged between 17m2/g and 54m2/g. The estimated values using Atterberg limits were slightly higher. The calculated and measured values of the external specific surface area differed by 0.6–6m2/g. [Copyright &y& Elsevier]

Abstract: In soil mechanics, the plasticity of fine-grained soils is expressed using the plasticity index. This represents the difference between the water content at the liquid and plastic limits, which are often collectively referred to as the Atterberg (or consistency) limits. They are of key importance in soil mechanics because they determine, in a simple way, the interaction between the solid and liquid phases in soils, and thus provide the possibility to classify soils into groups with similar mechanical properties. As the Atterberg limits are the most distinctive and the easiest property of fine-grained soils to measure, several researchers have tried to use them to predict various mechanical properties, such as the normalized, undrained shear strength of fine-grained soils. The most widely used expression for predicting this value from the plasticity index was suggested by Skempton. Since then, there have been several studies to examine the validity of his relation. A lot of the data agree with this relation; however, there is an equally large volume of data that contradicts it. The present study shows that the correlation between the normalized undrained shear strength of cohesive soils and the plasticity index really exists, but it is not as simple as was suggested by previous studies. By considering the mineralogical properties of clay minerals and their impact on the quantity and state of water in soils, it was found that there is no uniform criterion to determine the normalized undrained shear strength from the plasticity index for all fine-grained soils. [Copyright &y& Elsevier]

Abstract: Hydraulic conductivity is one of the important, basic engineering properties of soils. However, as a soil parameter it is difficult to measure and can be highly variable, necessitating the investigation of a large number of samples. For these reasons several researchers have proposed various indirect methods for predicting the hydraulic conductivity of soils from easily measured and routinely obtainable data. As plasticity is the most distinctive and the easiest property of clays to measure, it would be a very convenient basis for predicting the hydraulic conductivity. This paper focuses on an investigation of the relationship between the hydraulic conductivity of clays and their Atterberg limits. For this purpose five samples of expanding and non-expanding clays were used. The results of laboratory tests showed that the hydraulic conductivity of a clay at a selected void ratio could be adequately determined when the external surface area of the clay grains was considered. The finding that there exists an exactly defined relationship between the Atterberg limits of clays and their external specific surfaces helped us to express the hydraulic conductivity in terms of the void ratio and the plasticity value. [Copyright &y& Elsevier]