Role of composition and fabric of Kuttanad clay: a geotechnical perspective

Kuttanad clay from Kerala, India is a soft soil with associated problems of low shear strength and compressibility. An attempt is made to characterize the soil in terms of its mineralogy, fabric, organic matter, and pH in order to understand its geotechnical behavior and suggest a suitable ground improvement technique. It was found that the soil has a unique combination of minerals such as metahalloysite, kaolinite, iron oxides, and aluminum oxides. The diatom frustules present in the soil indicate biological activity during the sediment formation, and this also accounts for the nature of organic matter predominantly present in the soil, which is mostly derived from planktonic organisms. A considerable amount of organic matter is present in the soil, and the magnitude measured accounts to about 14 % by mass. The soil is found to be acidic and the low pH to some extent can be connected to the partial oxidation of pyrite. The aggregated-flocculated fabric, as deduced from the scanning electron microscopy images, is supported by comparison of liquid limit with plasticity index and the shrinkage limit. Low specific gravity, high liquid limit, and relatively low plasticity index are explained due to presence of organic matter, silica frustules, and fabric. The influence of soil fabric and composition on the index properties of the soil is likely to bear a direct link to the corresponding influence on the engineering behaviour of the soil

Mini compaction test apparatus for fine grained soils

The standard and modified Proctor compaction tests are devised to establish dry unit weight-water content relationships for a soil under controlled conditions, such as compactive effort, water content, etc. This paper presents a mini compaction apparatus primarily for use in fine grained soils, which requires only about 1/10th volume of soil needed for the standard and modified Proctor test. Additionally, the time and effort involved in carrying out the compaction test is much less. Also, the compacted soil sample, after trimming, can be used for strength tests

Potential of fly ash to suppress the susceptible behavior of lime-treated gypseous soil

The use of lime and fly ash to improve the properties of certain types of soil is well established. However, the potential of fly ash to control the adverse effects of lime-treated gypseous/sulphatic soil has not been well investigated. In the present work, an attempt is made to quantify the fly ash content used to suppress the susceptible behavior of lime-treated gypseous soil. Series of one-dimensional swell and compressibility analyses are performed on various combinations of expansive soil with a predominance of montmorillonite mineral containing lime, gypsum (0-6%), and fly ash (0-30%). It is observed that the volume change behavior of the lime-treated gypseous soil is not controlled completely by addition of fly ash. However, the maximum improvement in the volume change behavior of the lime-treated gypseous soil is observed with a 20% fly ash content, and hence, can be taken as the Optimum Fly ash Content (OFC). Microanalyses revealed that the relative dominance of the change in gradation and the formation of cementitious compounds of different compositions and ettringite crystals are the key factors in controlling the volume change behavior of lime-treated gypseous soil with fly ash. However, several factors, such as the types of minerals present in the soil, the types of fly ash and lime, and other physico-chemical environmental conditions (temperature, method of curing, and so on), are seen in the present study to affect the value of the obtained OFC. (C) 2018 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society

Electro-Kinetic Remediation of Sulphate from Soil

Decontamination of fine-grained soils from ionic pollutants by conventional methods is not only costly but also mostly ineffective because of their low hydraulic conductivity, low biodiversity, and strong adsorption on their surface. To decontaminate soils of low hydraulic conductivity, the application electrical potential along with passing of water under hydraulic gradient has come into vogue. This method is called electro-kinetic remediation. The efficiency of removal of cations near cathode is well established, the removal of anions at anode is not that effective. In this case, the electrical potential causes the migration of anions towards the anode is inhibited by opposing osmotic flow. Hence, the removal of anions by electro-kinetic extraction method is less effective compare to cations, how it will affect the sulphate ion migration has been studied in this paper. From the study, it has been observed that the breakthrough curve of sulphate ion under electrical potential is significantly lower than under advection and diffusion only. It is also concluded that inspite of electro osmotic flow occurring in the opposite direction, the breakthrough of sulphate occurs earlier because of migration of sulphate ion towards anode under electrical gradient

Liquid limit of soil mixtures

The liquid limit test is one of the most widely used tests in the soil engineering practice. Several properties, including mechanical properties (for example, compressive index), have correlations with the liquid limit. In this paper detailed investigations of the liquid limit of soil mixturs have been carried out using bentonite, kaolinite, sand (coarse grained, fine grained, rounded and angular shaped), and silts. Based on the results obtained, it has been shown that the liquid limits of soil mixtures are not governed by the linear law of mixtures. While the shape of the sand was not found to influence the liquid limit, the size of the sand particles had a definite influence. Liquid limit obtained by the cone method is lesser than the limit obtained by using the Casagrande apparatus. A good relationship exists between the results of these two methods. A procedure for obtaining the liquid limit of low plastic soil has been suggested

Volume Change Behavior of Gypseous Soil

The susceptible characteristics of gypseous soil with variations in water content pose several engineering problems due to volume change behavior. A series of oedometer tests have been performed to understand the swell strains and compressibility of soil containing varying gypsum content after curing for different periods. The swell strains of both uncured and cured samples increase with an increase in gypsum content up to 2% and decrease with a further increase in gypsum content. However, the swell strain of soil with any gypsum content decreases with an increase in the curing period. The compressibility of the soil increases with an increase in gypsum content but decreases after curing for longer periods. However, the effect of curing is minimal on the compressibility of soil containing a higher gypsum content. The permeability of gypseous soil increases along with an increase in the total change in void ratio upon loading. Detailed microanalyses have revealed that an increase in the swell strains and compression in soil with lower gypsum is due to the formation of zeolite and a weaker cemented matrix. However, the presence of unreacted gypsum particles in the soil matrix and the suppression of zeolite with the formation of cementitious compounds reduce the swell strains and compression with higher gypsum after curing for longer periods. (C) 2017 American Society of Civil Engineers

Swelling behaviour of soil-bentonite mixtures

Studies on the swelling behaviour of mixtures of bentonite clay and nonswelling coarser fractions of different sizes and shapes reveal that observed swelling occurs only after the voids of the nonswelling particles are filled up with swollen clay particles. The magnitude of the swell within the voids, called intervoid swelling is large when the size and percentage of the nonswelling coarser fraction is large. The observable swell, after intervoid swelling, is called primary swelling and follows a rectangular hyperbolic realtionship with time. The total swell per gram of the clay decreases with an increase in the size of the nonswelling fraction and with a decrease in the percentage of swelling clay. Time swell realionships show that swelling continues to occur for a long time after the primary swelling, and this is called secondary swelling

Physical and strength development in lime treated gypseous soil with fly ash - Micro-analyses

An attempt has been made to examine the role of fly ash content (0-30%) to control undesirable strength loss in lime-treated expansive soil containing gypsum (0-6%) after curing for different periods up to one year. Further, detailed experimental investigations have been performed to assess the plasticity, swell index and compaction behavior of soil treated with these additives. Results of the strength behavior revealed that a significant effect of higher fly ash content in the strength development of lime-treated soil is observed after longer curing periods. Presence of increasing amounts of gypsum accelerates early strength gain initially, but reduces long-term strength gain in soil-lime-fly ash mixes. Fly ash improves the strength of lime-treated gypseous soil. However, beneficial use of fly ash to improve the strength of lime treated gypseous soil depends on the amount of gypsum present in the soil and length of curing periods. Micro-analyses (XRD and SEM) revealed that the strength development is controlled by reaction products formed such as cementitious compounds and ettringite crystals

Influence of Sodium and Lithium Monovalent Cations on Dispersivity of Clay Soil

Exchangeable sodium ions are widely reported to be the principal reason for the dispersivity of soils. From fundamental theoretical considerations, several other factors such as pH, cation exchange capacity, mineralogy, electrolyte concentration, and dissolved salts can affect the attractive/repulsive forces in soils and hence are considered to have a significant role in assessing the dispersivity of soils. To assess the influence of these parameters, a known dispersive soil was treated with sodium hydroxide and lithium hydroxide and the dispersivity was assessed. It was confirmed that the effects of these factors on dispersivity are manifested through the amount of hydration of the adsorbed monovalent cations. Because the inner hydration shell of adsorbed monovalent cations is larger than those of higher-valency ions, dispersivity is related to the presence of monovalent cations alone. It was also established that within the monovalent cations, the size of hydrated ions can vary and can influence the dispersivity of the soil. The dispersivity of soils increased with a reduction in the size of the ions. The increase in repulsive force (causing dispersion) due to the reduction in the size of the cation is explained through diffuse double layer theory. A complete philosophy of dispersion is proposed in light of the current experimental results

Delay in compaction and importance of the lime fixation point on the strength and compaction characteristics of soil

The importance of the lime fixation point on the strength of fine-grained soil hardly needs to be stressed. The improvement in strength of soils with lime contents below and above the lime fixation point occurs by different mechanisms. Further, the strength is also influenced by moulding water content and dry density. The time lag between wet mixing and compaction plays a major role in the application of lime to fine-grained soils. This paper highlights the importance of the lime fixation point on the compaction characteristics of expansive Indian black cotton soil. The effect of delay below, at and above the lime fixation point on the compaction and the strength characteristics is presented. Below the lime fixation point, lime addition steeply decreases the maximum dry density and marginally improves the strength. Here the strength is significantly influenced by the moulding water content. Delay between wet mixing and compaction is less critical below the lime fixation point. For soil with a lime content above the lime fixation point there is no further change in the compaction curve. The strength improves considerably above the lime fixation point and is not controlled by moulding water content. Further delay in compaction for the soil above the fixation point steeply reduces the maximum dry density and strength. At about the lime fixation point the effect is in between the two extremes