Free Swell Ratio Research Articles

Closure to “Quantitative Estimation of Clay Mineralogy in Fine-Grained Soils” by Bhaskar Chittoori and Anand J. Puppala

The authors’ contribution is a welcome addition to the literature. It brings out the importance of clay mineralogy in solving engineering problems connected with soil improvement techniques. The engineering behavior of fine-grained soils is controlled by the clay mineralogical composition of the soil. As discussed by the authors, soils of similar plasticity characteristics can contain different dominant clay minerals. Hence, it is correctly indicated by the authors that identical stabilization design or treatment cannot be given to soils with identical plasticity characteristics without the proper knowledge of the dominant clay minerals composing the soils. In fact, this is the major limitation of the plasticity chart used to classify finegrained soils. Hence, it is important to recognize the dominant clay mineral composition of soils in any project dealing with finegrained soils. The authors have proposed a methodology of quantifying the clay mineral composition of soils, which considers montmorillonite, illite, and kaolinite to be the major and stable clay mineral types, for which they deserve appreciation. The study of the paper under discussion reveals the following points: • The quantification of clay minerals in the soils with the available procedures such as X-ray diffraction, scanning electron microscopy, or infrared spectroscopy is not that simple to adopt. Sophisticated instrumentation and interpretation techniques are required. • The quantification of the dominant clay minerals in the soil by the method proposed by the authors requires information such as cation exchange capacity (CEC), specific surface area (SSA), and total potassium content (TP). The determination of these quantities, particularly SSA, is also not that simple. Hence, the proposed method is not user friendly. • There is no definite relationship between quantities such as CEC or SSA and the quantities of montmorillonite illite and kaolinite minerals predicted. In this context, the discussers feel that the exact percentage quantification of the clay minerals present in the soil is not required to judge the clay soil behavior. They opine that it is sufficient enough to classify the soils in to different groups based on their degree of expansivity, which is an indirect representation of the dominant clay mineralogy of soils. Sridharan and Prakash (2000) conducted a detailed analysis of the swelling capabilities of a number of soils of varying plasticity characteristics and varying clay mineralogical composition obtained from oedometer swell tests on soils, which give the most useful and reliable assessment of swell capacity of soils (Chen 1975; Winterkorn and Fang 1986) from air dry to saturated conditions under a surcharge of 7 kPa, in the compacted condition, and from other soil parameters such as liquid limit, plasticity index, and activity. Their analysis indicated that liquid limit, plasticity index, and activity cannot satisfactorily predict soil expansivity, because they do not consider the effect of soil clay mineralogy. On the basis of that analysis, they proposed a very simple and user-friendly methodology for the prediction of degree of soil expansivity and dominant clay mineral type present in the soil based on the free swell ratio (FSR), which compares exceedingly well with those from the oedometer swell tests. The FSR is defined as the ratio of the equilibrium sediment volume of a 10-g oven-dried soil sample passing through a 425mm sieve placed in a 100-mL graduated measuring jar containing distilled water (Vd) to that in carbon tetra chloride/kerosene (Vk), thoroughly mixed, and left for the sediment formation, after an equilibration period of a minimum of 24 h

Test study of high liquid limit clay modified by quick lime used as sub-grade material

Through laboratory test, the relationships among change of compactibility, liquid/plastic limit, free swell, swell ratio without load, california bearing ratio (CBR) and soakage (after being soaked in water), and mix-ratio of quick lime and time were studied. The results show that optimum water content, plastic limit and CBR of high liquid limit clay improved by quick lime increase with the increase of mix-ratio of quick lime, while the maximum dry density, liquid limit, plasticity index, soakage (after being immersed in water), free swell, and swell ratio without load decrease with the increase of mix-ratio of quick lime. Plastic limit of high liquid clay improved by quick lime gradually increases with time, while the liquid limit, plasticity index, free swell and swell ratio without load gradually decrease with time. When the mix-ratio of quick lime exceeds 2%, after 14 d, swell ratio without load of the improved clay is zero, its free swell is about 30% of that of untreated soil, and its plasticity index is less than 26 for sub-grade material, satisfying the requirement by ‘Specifications for Design of Highway Subgrade’.

Theory and practice concerning classification for expansive soils using standard moisture absorption water content

A series of tests on physical, mechanical and chemical properties of expansive soils have shown that the standard moisture absorption water content (SMA) of expansive soils has a good linear relationship with montmorillonite content, cation exchange capacity, specific surface, and it also presents a linear relationship tendency to plastic index and free swell ratio. All this indicates that the above SMA is of clear significance in physics. The plastic index can better reflect the interaction extent between composition and dispersing character of grains, cation and clay minerals. Consequently, SMA can reflect the basic essential properties of expansive soils. On the basis of the classification results that have been published in literature and in consideration of the succession to the classification results for the free swell ratio, this paper puts forward three indexes, i.e. the SMA, plastic index and free swell ratio to classify expansive soils. The tests proposed for the classification indexes are easy to operate, simple in testing device and last a short time. Compared with the latest issued “Classification Standard Code for Rocks and Soils of Railway Projects” (TB10077-2001), the method proposed in this paper is more convenient and reasonable, and can be popularized, when environment conditions ripen, for the application in field of exploration and design of highway in the areas surrounded by expansive soils.

Free Swell Ratio and Clay Mineralogy of Fine-Grained Soils

Abstract The dominant clay minerals present in fine-grained soils control the physical and engineering behavior of the soils. Determination of the dominant clay minerals in the soils, at present, requires procedures involving sophisticated instrumentation and the knowledge to interpret the results from such tests. A user-friendly approach based on free swell ratio, defined as the ratio of the equilibrium sediment volume of 10-g oven dried soil in distilled water to that in carbon tetra chloride, has emerged as a simple methodology to predict the clay mineral(s) present in the soil as either montmorillonitic or kaolinitic type quite satisfactorily. The validation of the proposed free swell ratio method has been done with exhaustive experimental data.

Classification procedures for expansive soils

Most of the national codes of practice do not give characterization and classification of expansive soils, in spite of expansive soils being distributed very widely over almost all geographical locations in the world, causing distress to the structures founded on them and discomfort to the users. A simple user-friendly approach based on the free swell ratio, defined as the ratio of the sediment volume of soil in distilled water to that in carbon tetrachloride or kerosene, is formulated considering the compatibility of the results with oedometer free swell tests and the soil clay mineralogy. Statistical illustrations are provided which clearly indicate that while the assessment of soil expansivity based on index properties is an overestimation, there is a consistency in the classifications based on oedometer test results and the proposed approach. It is recommended that simple approaches such as the one proposed here to classify the expansive nature of soils are entered into standard codes of practice.