Engineering Characteristics and Performance of Polypropylene Fibre and Silica Fume Treated Expansive Soil Subgrade

This study presents the experimental results of the effective utilization of polypropylene (PP) fibre and silica fume (SF) to stabilize the expansive soil subgrade as a possible alternative from the environment, economic, and technical perspective. During the drying cycle, clayey soil undergoes unpredictable shrinkage deformation. The nonrecurring shrinkage behaviour of expansive soil caused the adverse effect on lightweight civil engineering structures. Therefore, expansive soil is not considered suitable subgrade material for paved structure construction. Paved structures constructed on clayey soil subgrade experience severe damages occur in its life cycle. The numerous mechanical, biological, and chemical techniques have been successfully demonstrated to reduce the swelling-shrinkage nature and improve the strength behaviour of expansive soil subgrade. This study aims to utilize industrial waste SF as chemical and PP fibre as a mechanical stabilizer. The mecho-chemical stabilization of expansive soil has been carried out by reinforcing the expansive soil with PP fibre and chemically stabilizing with SF. To evaluate the performance of waste material as a stabilizer, compaction, Atterberg's limits, free swelling index (FSI), electrical conductivity (EC), pH, swelling pressure, and California bearing ratio (CBR) tests have been conducted on treated and untreated specimens. Over the past few years, images from digital cameras have been successfully used to study crack morphology and various parameters of soils. The image processing technique has been used to evaluate the shrinkage limit by developing the MATLAB program code. The microstructural analysis has been carried out using scanning electron microscopy (SEM) analysis. The varying percentage of silica fume (2%, 4%, and 8%) and polypropylene fibre (0.25%, 0.5%, and 1%) by weight of dry soil were used to stabilize the expansive soil. The results show that the value of CBR increases and the shrinkage area decreases with an addition of SF and PP fibre. The experimental results also show a reduction in Atterberg's limit with the addition of SF and PP fibre; as a result, the shrinkage behaviour of clayey soil reduces exponentially. The digital image processing technique showed a higher potential to understand the soil morphology for the large area.