Influence of adding gypsum on the properties of lime-stabilized expansive soil

Abstract Expansive soils present major structural and geotechnical engineering problems. Expansive soil undergoes considerable changes in volume because of variations in water content. These variations in volume can occur as either swelling or shrinking and are commonly referred to as swell-shrink soils. Considering key aspects, such as the characteristics of the soil, is essential when dealing with swelling soils. There are expansive soils in both humid areas, where they pose problems with a high plasticity index, and in semi-arid or arid areas, where even moderately swelling soils can cause considerable damage. In order to solve problems related to expansive soil, it is important to stabilize it using various additives like gypsum, lime, and so on. The effects of adding three percentages of gypsum (2%, 4%, and 8%) to 6% lime-stabilized expansive soil to improve its engineering properties are investigated through several tests. The results of tests displayed that adding gypsum has improved properties of prepared soil with 6% lime. The optimum mixture for (gypsum-lime) that gets the highest improvement in soil properties is (6% lime + 4% gypsum). This mixture shows reducing in the free swell, swelling pressure, and plasticity index (from 8.51% to 2.81%, from 715.68 Kpa to 89.18 Kpa, from 33% to 29% respectively). Also, this mixture shows increasing in CBR (from 13.69% to 16.17%) and unconfined compressive strength (UCS) for the curing time of 0, 7, and 14 days (from 264.318 Kpa to 492.131 Kpa, from 380.584 Kpa to 736.318 Kpa, and from 480.192 Kpa to 828.590 Kpa respectively). The maximum dry density (MDD) and optimum moisture content (OMC) increase with increasing gypsum content, While the specific gravity decreases.