<p>Plastic waste is a growing global concern, with only a small percentage of packaging being recycled. In response, sustainable engineering is seeking innovative methods to integrate waste materials into geotechnical applications. This study examines recycled high-density poly ethylene (HDPE) pellets and slurry for improving piping resistance in silty sand used in hydraulic structures. The study aimed to assess how reprocessed plastic affects the critical hydraulic gradient, indicating soil’s resistance to piping. A custom laboratory setup was employed to simulate upward seepage conditions, and soil samples were reinforced with varying proportions (0.5–3.0%) of plastic additives. The methodology involved controlled compaction and saturation of samples, followed by one-dimensional piping tests using permeameters under standardized conditions to analyze seepage behavior. Results showed that both HDPE pellets and slurry enhanced soil piping resistance, with peak performance at 2.5% slurry and 2.0% pellets. Slurry offered greater improvement in the critical hydraulic gradient but involved more complex preparation and safety concerns. The improvement was due to altered flow paths and increased soil cohesiveness. For the present study, it is concluded that adding recycled HDPE to soil significantly enhances its resistance to piping, offering a sustainable and cost-effective solution for embankments and hydraulic structures.</p>