Nagaraj Hb

For Black cotton (B.C.) soils many alternate stabilization techniques are being suggested by researchers from time to time, which partially address the problem of volumetric instability with moisture changes. Of late, with the success of the enzymatic stabilization of kaolinitic soils, researchers have tried to extend the application of enzymatic stabilization to B.C. soils. The reported information in the literature on index properties of enzyme treated B.C. soils is very intriguing. In this study, two different formulations of a commercially available TerraZyme (TZ 5X and TZ 11X) with four selected dosages were used to understand the changes in index as well as undrained strength properties with ageing of two B.C. soils selected from different geological locations. Contrasting changes in plasticity properties on enzymatic treatment using TZ 5X with ageing are observed for the two B.C. soils used in the present study. However, TZ 11X has shown to have a slight reduction in liquid limit and an increase in shrinkage limit. As index properties are inferential properties of soils, changes in plasticity properties by using enzymes may not be the only indication of the effectiveness of enzymatic stabilization. Enzyme treated soils yielded a marked improvement in undrained strength indicating a better parameter to assess the effectiveness of enzymatic stabilization of B.C Soils.

Shrinkage limit is one of the important parameters among the Atterberg limits used to classify fine-grained soils and to express its volume stability. Conventional method to determine volume of wet and dry shrinkage pats to evaluate shrinkage limit involves the usage of mercury, which is highly toxic and hazardous to health. Recently various methods have been proposed by different researchers which do have certain shortcomings. The present study proposes a simple and alternate method to determine the volume of dry shrinkage pat with the use of hydrophobic compound and water submersion method, which is required to calculate the shrinkage limit of soils, thereby overcoming the various shortcomings of the alternate methods proposed by different researchers in the recent past. Three hydrophobic compounds, namely Vaseline, hydrophobic liquid, and hydrophobic glue were used to coat the dry shrinkage pats with a thin layer of these compounds and make them hydrophobic, and hence, determine their volume with water submersion. The results of shrinkage limits of soils used in this study obtained using all these three hydrophobic compounds are within the acceptable range as suggested by ASTM standard D427-04 (Test method for shrinkage factors of soils by the mercury method, ASTM International, West Conshohocken, 2004. https://doi.org/10.1520/d0427-04) and ASTM standard D4943-02 (Standard test method for shrinkage factors of soils by the wax method, ASTM International, West Conshohocken, 2008. https://doi.org/10.1520/d4943-08) for any two results obtained from two different tests of the same type, for multi-laboratory determinations. The proposed alternate method of determining the shrinkage limit is not only simple but also reliable. It can be verified by various researchers before it can find universal acceptance as a standard and alternate method of determining the shrinkage limit of soils.

Plasticity properties of fine-grained soils in the form of Atterberg limits are very important inferential properties used for classification and preliminary qualitative assessment of their suitability for any geotechnical engineering applications. Through extensive research, it is well understood that clay mineralogy and soil structure are the main factors that control the Atterberg limits of soils. To further the understanding of the factors influencing the Atterberg limit of soils at the macro level with an insight at the micro level through SEM studies, the present study was taken up using various soil mixtures prepared with extreme clay minerals (Bentonite and Kaolinite), fine sand, and silt (extracted from a natural soil). From the experimental results reported herein, the changes observed in the Atterberg limits as influenced by the variation in the composition of the fractions in the clay-sand-silt mixture may be due to the influence of clay mineral type and the clay structure which are supported by the SEM images.

Predicting the coefficient of volume compressibility (m_v) would help a field engineer to make a quick estimate of the soil compressibility. The multiple correlations suggested by various researchers as available in the literature indicate the importance of predicting the m_v of soil. The existing correlations as available in literature either use soil state (in the form of SPT N-value or unconfined compressive strength or natural water content) or soil type (in the form of plasticity properties). However, using both soil type and soil state parameters in developing any prediction equation would be more reliable. To overcome this limitation of existing correlation equations to predict m_v, a simple and reliable method that can be universally applied with appropriate soil type parameter represented by the Shrinkage Index (Liquid Limit-Shrinkage Limit) and soil state parameter represented by standardized SPT N₆₀ has been proposed. This model is designed to be universally applicable, serving as a valuable tool for practicing engineers and researchers to predict m_v.

The main focus of the criticisms raised by O'Kelly and Soltani (2025) (hereafter referred to as discussers) to the authors' article in Bulletin of Mineral Research and Exploration (174, 1-10) is to examine the veracity of the strength-based equations presented by Kayabalı et al. (2024). The discussers applied the predictive equations proposed by the authors to dissimilar soils in the two articles (Kayabalı et al., 2015a; Kayabalı et al., 2015b) published earlier by the lead author with his research group. The discussers showed that the predictive equations 6 and 7 given by Kayabalı et al. (2024) yield extremely high values of liquid limit (LL) and plastic limit (PL) when applied to dissimilar soils. Further, discussers argued that the approach proposed by Kayabalı et al. (2024) led to erroneous results in determining soil classes.

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This article concludes the Discussion on the Geotechnical Testing Journal, GTJ-2022-0093, with three objectives: (1) clarifying the meaning of “consistency” and “toughness,” (2) elaborating the combined qualitative and quantitative approach, and (3) justifying the practicality of the Manafi method for a wide range of fine-grained soils regardless of their soil type.