Effects of Non-plastic Fine Addition on the Swelling Indices of Expansive Soil

Abstract: Expansive behavior in soil is primarily due to the presence of fine-grained clay minerals, which have flaky particle shapes and large specific surface areas. These factors result in an affinity for water, leading to the swell-shrink phenomenon and causing extensive distress in soil. This distress can result in cracking, displacement, and other forms of damage to structures built on expansive soil, which can cause significant financial losses. One possible solution to mitigate the swelling behavior of expansive soil is to add non-plastic fines to the soil. Non-plastic fines, such as sandy soil, are less likely to shrink and swell due to their bulkier particle shape and lower specific surface area. This study evaluated the effectiveness of adding non-plastic fines (sandy soil) in reducing the swelling behavior of expansive soil. The experimental program involved the preparation of soil specimens with five different sand contents (i.e., 0%, 10%, 15%, 20%, and 25% by dry weight of soil) to determine the optimum concentration of sandy soil that would provide the maximum reduction in swelling behavior. The swelling properties were evaluated regarding swelling potential, swelling pressure, free swell index, linear shrinkage, and plasticity index. The study results indicated that sandy soil effectively reduced the swelling behavior of expansive soil. The swelling pressure of the soil with 10% sand content was measured to be 144 kPa, representing a 54% decrease from the 311 kPa swelling pressure observed in the untreated soil. The initial moisture content of the soil had a significant influence on swelling potential. As the initial moisture content increased, the swelling potential reduced, suggesting that the initial moisture content of the soil should be carefully controlled to minimize the swelling behavior of expansive soil. The findings of this study can be useful to agencies aiming to address the adverse impact of expansive soil on civil infrastructures.