T Thyagaraj

Expansive soils in the field are subjected to swelling and shrinkage due to seasonal moisture variations. Most of the previous studies on swell-shrink were carried out by direct mixing of stabilizer with soil and very few studies have been carried out on swell-shrink behaviour of expansive soil stabilized through permeation. Hence, in the present study, an attempt is made to study the swell-shrink behaviour of expansive soil through laboratory tests using lime slurry (LS) and lime pile (LP) techniques and the two results are compared. In laboratory the LS were permeated through the central hole of expansive soil in the desiccated state, whereas, the LP was installed in compacted expansive soil. Undisturbed soil specimens were collected from LP and LS-treated expansive soil in the test moulds after a curing period of 30 days for evaluation of swell-shrink behaviour at a radial distance of 1.5d (where d = diameter of central hole) and at depths of 0–90 mm and 200–290 mm for LS and LP-treated soils. The study shows that in LS-treated specimens the volume change increases with an increase in number of wet-dry cycles for the specimen taken at a depth of 0–90 mm, which shows the loss of cementation bonds. Whereas, LS-treated samples taken at a depth of 200–290 mm and LP-treated samples collected at a depth of 0–90 mm and 200–290 mm did not show any improvement in controlling the swell-shrink behaviour of expansive soil.

This paper presents a comparative study of stabilization of expansive soil using lime pile and lime precipitation technique. Lime precipitation was carried out by sequential permeation of calcium chloride (CaCl2) and sodium hydroxide (NaOH) solutions through a central hole in the compacted expansive clay. Similarly, lime pile was installed in a central hole of compacted expansive soil. After 30 days of curing, the undisturbed soil specimens were collected from different radial distances for evaluation of physico-chemical, index, and engineering properties. Microstructural changes were captured using scanning electron microscopic (SEM) images and electron dispersive X-ray spectroscopy analysis (EDAX) for both treated and untreated soils. The index and engineering properties of treated soils indicate that the lime precipitation treatment was effective up to a radial distance of 2.5 d from the central hole of diameter, d, while the lime pile treatment was limited to a radial distance of less than 0.8 d.

Sequential permeation of calcium chloride and sodium hydroxide solutions into the soil mass leads to the formation of lime in the in-situ soil mass owing to chemical reactions. Previous studies have demonstrated that the lime precipitation modifies the expansive soil properties both by lime modification and pozzolanic reactions. However, the independent contributions of either calcium chloride solution or sodium hydroxide solution in stabilizing the expansive soil are not known. Therefore, an attempt is made in the present investigation to examine the relative efficiencies of calcium chloride solution, sodium hydroxide solution and lime precipitation in stabilizing the expansive soil by comparing the physico-chemical and index properties, oedometer swell potentials and unconfined compressive strength of treated specimens. The present investigation also brings out the relative efficiencies of hydrated lime and precipitated lime in stabilizing the expansive soil. The experimental results showed that treating the expansive soils with calcium chloride and sodium hydroxide solutions independently promoted only the short-term reactions whereas the sequentially treating the expansive soil with calcium chloride and sodium hydroxide solutions resulted in the formation of lime precipitation, which could mobilize both short-term lime-modification reactions and long-term soil-lime pozzolanic reactions.

In-situ deep Figure 14stabilization of expansive soil deposits is commonly carried out using lime piles and lime slurry injection. Recent research demonstrated the stabilization of expansive soils using lime column technique, and more recently the lime precipitation technique has emerged as the viable choice for stabilization of expansive soils. Comparison of these techniques in stabilizing the expansive soils provides a better understanding of the stabilization mechanisms and their advantages and limitations. Therefore, this paper brings out the relative efficacy of different lime treatment techniques in stabilizing the expansive soils. To achieve this objective, the laboratory model tests were carried out in expansive soil using lime pile and lime precipitation techniques in a compacted state, and lime slurry technique in a desiccated state from a central hole of diameter, d. The lime precipitation was achieved by sequential permeation of 46.2% calcium chloride and 33.3% sodium hydroxide solutions through a central hole in the compacted expansive soil. After 30 days of curing in the test moulds, the undisturbed soil specimens were collected for evaluation of the changes in physico-chemical, index and engineering properties. The experimental results reveal that the treatment is effective in stabilizing the expansive soil up to a radial distance of 0.8d from the central hole in case of lime pile treatment, whereas the lime slurry treatment up to a radial distance of 1.5d and lime precipitation treatment up to a radial distance of 2.5d. The experimental findings were supported with scanning electron microscopic images and energy dispersive X-ray spectroscopy analysis.