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Environmental and Engineering Geoscience

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Changes in Swell Behavior of Expansive Clay Soils from Dilution with Sand

¹ Division of Engineering, University of North Florida, 4567 St. Johns Bluff Road South, Jacksonville, FL 32224
² Scott Wilson Kirkpatrick & Co., Ltd., Royal Court, Basil Close, Chesterfield, Derbyshire S41 7SL, UK

Volume changes associated with expansive soils cause considerable distress to lightly loaded engineered structures, especially slab-on-grade residential structures, roadways, and masonry block walls. There are numerous techniques, such as physicochemical stabilization, mechanical stabilization, and preventative practices, that are recommended for mitigating the effects of expansive soils. In this paper, two expansive soils from southern Nevada were mixed with varying percentages of fine silica sand, and a series of laboratory tests were conducted on the soil mixtures to assess changes in soil classification, plasticity index, swelling behavior through surcharge expansion tests, and potential volume change (PVC) tests. Additionally, the clay mineralogy was determined by x-ray diffraction. For both soils, an increase in the percentage of mixed silica sand by 0 to 75 percent decreased the plasticity index such that the soils were categorized as non-expansive or having very low swell potential. The relationship between plasticity index and percentage of added sand was described using a simple dilution model. The swell characteristics of the soils, based on surcharge expansion tests and potential volume change tests, decreased with increasing percentages of mixed silica sand, and non-soil-specific empirical models were developed to predict the changes. These experiments show that soil mixing is a promising technique that could be implemented to mitigate the effects of expansive soils.

Key Words: Expansive Soils • Soil Mixing • Plasticity Index • Swell Potential • Potential Volume Change • Swell Index • X-Ray Diffraction