Expansive clay soils pose a challenge for building foundations because they change volume with moisture levels. This volume change may cause foundations to move unevenly, causing structural trouble. This research checks how using recycled synthetic fibers can change how these soils act, which in turn affects how they affect foundations. Laboratory tests were done to see how adding fibers affects the soil's swelling, strength, and stiffness. The data from these tests was used to create a computer model to predict how the soil and a foundation would act together under typical conditions. The results suggest that fibers can greatly reduce swelling and improve how the soil performs. Foundations built on these improved soils could see less uneven settling and a better distribution of weight. The use of both natural and recycled fibers is a sustainable alternative to chemicals for soil stabilization, with a smaller footprint on the environment. This study suggests that reinforcing soil with fibers is a useful and environment-friendly way to improve soil-structure interaction where expansive clays are present.