This paper addresses the behaviour of compacted expansive soils under swellshrink cycles. Laboratory cyclic swellshrink tests were conducted on compacted specimens of two expansive soils at surcharge pressures of 6.25, 50.00, and 100.00 kPa. The void ratio and water content of the specimens at several intermediate stages during swelling until the end of swelling and during shrinkage until the end of shrinkage were determined to trace the water content versus void ratio paths with an increasing number of swellshrink cycles. The test results showed that the swellshrink path was reversible once the soil reached an equilibrium stage where the vertical deformations during swelling and shrinkage were the same. This usually occurred after about four swellshrink cycles. The swelling and shrinkage path of each specimen subjected to full swelling full shrinkage cycles showed an S-shaped curve (two curvilinear portions and a linear portion). However, the swelling and shrinkage path occurred as a part of the S-shaped curve, when the specimen was subjected to full swelling partial shrinkage cycles. More than 80% of the total volumetric change and more than 50% of the total vertical deformation occurred in the central linear portion of the S-shaped curve. The volumetric change was essentially parallel to the saturation line within a degree of saturation range of 5080% for the equilibrium cycle. The primary value of the swellshrink path is to provide information regarding the void ratio change that would occur for a given change in water content for any possible swellshrink pattern. It is suggested that these swellshrink paths can be established with a limited number of tests in the laboratory.Key words: expansive soils, oedometer tests, swellshrink behaviour, shrinkage tests.
This study examines the impact of varying the compaction (dry) density and water content on the swelling behavior of desiccated clay soil. Specimens in the shrunken state that have a history of four cycles of wetting and drying are referred to as desiccated specimens in this study. Experimental results showed that the volumetric swell potentials of the desiccated soil specimens were independent of their compaction water contents, but were strongly influenced by their initial void ratios. Comparatively, the vertical swell potentials of the desiccated specimens were independent of their initial water contents and initial void ratios. The results of this study indicated the existence of an optimum void ratio for the examined compacted specimens. Specimens compacted to this void ratio exhibit similar volumetric swell potentials in the as-compacted state and after cycles of wetting and drying.
Effect of aging on swelling and swell-shrink behavior of a compacted expansive soil is investigated in this paper. An expansive soil having a liquid limit of 100% is used for this purpose. Compacted specimens were prepared and aged for a predetermined number of days (7, 15, 30, and 90 days) to study their swelling and swell-shrink behavior. It has been shown that aging improves the resistance to compression of compacted specimens. The swelling potentials of specimens also decreased with aging. The dominant factors that influence the aging effects are the water content and degree of saturation at the beginning of the aging process. The changed behavior of aged specimens is attributed to particle rear-rangements and formation of bonds, which affect the surface area absorbing water during swelling. The cyclic swell-shrink tests on aged specimens indicated that the differences in vertical displacement during the first swelling were eliminated in the subsequent cycles when specimens were shrunk more, but the aging effect was found to persist with cycles for specimens subjected to lower shrinkage magnitudes.
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