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Lime continues to be one of the most popular chemical admixtures used to modify expansive clays despite the associated mixing and pulverization problems. In the present investigation, the efficacy of CaCl2 in place of conventionally used lime is studied by conducting laboratory and field tests. These investigations were carried out on the slopes of a trapezoidal trench made in expansive clay bed. Heave measurements were taken on the lime and CaCl2 treated slopes and also on untreated slopes for four consecutive cycles of wetting and drying. The field cyclic seasonal movements and the subsequent laboratory tests on undisturbed and disturbed soil samples revealed that the CaCl2 could be a promising chemical modifier instead of conventionally used lime, not only due to its multifold influence on heave control, plasticity reduction, and swell properties but also its easy application in the form of solution without any need for pulverization and mixing. Though an apparent reduction in unconfined compressive strength of treated samples is observed, the drained triaxial tests on treated and untreated samples revealed that there is an increase in the angle of internal friction of treated samples. [ABSTRACT FROM AUTHOR]

This paper presents, by way of comparison, the effect of fly ash on the volume change of two different types of clay, one a highly plastic expansive clay and the other a nonexpansive clay, also of high plasticity. Expansive clays swell on absorbing water and shrink on drying. Nonexpansive clays undergo large compression at high water contents. The effect of fly ash content on free swell index, swell potential, and swelling pressure of expansive clays was studied. Compression index and secondary consolidation characteristics of both expansive and nonexpansive clays were also determined. Swell potential and swelling pressure, when determined at constant dry unit weight of the sample (mixture), decreased by nearly 50% and, when determined at constant weight of clay, increased by nearly 60% at 20% fly ash content. Compression index and coefficient of secondary consolidation of both the clays decreased by 40% at 20% fly ash content. [ABSTRACT FROM AUTHOR]

Physicochemical interactions between polymer molecules and clay particles affect the swelling rate and magnitude of expansive clay soils. The effectiveness of aqueous solutions of three polymers: Sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), polyethylene oxide (PEO) ranging in concentration from 0.5 to 10 g/L, as soil stabilization agents against Na-montmorillonite swelling was analyzed. Rates of volumetric swelling of Na-montmorillonite upon hydration were recorded over durations ranging from 120 to 200 h, and data were used to compute the volumetric swelling ratio (VSR), an expression of the clay volume at any time relative to the initial volume of clay in the immersion tube. The results show that PAM, the cationic polymer reduces the VSR by as much as 40% relative to distilled water. PAM molecular weight and concentration have minimal effects on VSR although sorption of PAM of higher molecular weight (PAM B) is favored at aqueous concentration below 2 g/L. Data from x-ray diffraction and batch sorption tests on dried Na-montmorillonite samples indicate that postsorption/swelling interlayer spacings of 0.74 and 0.78 nm for PAM A (molecular weight=4×106) and PAM B (molecular weight=7×106) respectively, are attained through fixation of PAM molecules in clay interlayer space during sorption at an aqueous concentration of 4 g/L. Test results for CMC (the anionic polymer) and PEO (the neutral polymer) show that swelling is not significantly reduced relative to that of distilled water. PAM can be used at aqueous concentrations between 0.5 and 4 g/L as an effective stabilization agent for expansive soils. [ABSTRACT FROM AUTHOR]