<p>Disposing of coffee ground wastes mainly causes a lot of time and energy, leading to environmental problems. This research aims to study the feasibility of Waste Coffee Particles (WCP) as a soil improvement agent that can be environmentally sound and efficient, improving the physical and mechanical properties of sandy clay soil. Tests were carried out with different percentages of WCP (5%, 10%, 15%, and 20%) in various soil mixtures. The experiments encompassed particle size distribution tests, Atterberg limit determinations, dry unit weight, gradations, void ratios, compaction, settlement, and triaxial shear tests to investigate the effect of WCP on soil deformation behavior. The results depict that the application of WCP increases the liquid and plastic limits, indicating improved moisture retention capacity due to the organic and porous nature of coffee particles. However, specific gravity and dry density decrease as WCP content increases, suggesting its suitability for lightweight fill applications. The optimum moisture content increases, supporting better water absorption and retention. The study concludes that 10% WCP is optimal for non-structural uses such as erosion control, light embankments, and drought-resilient landscaping. This research demonstrates WCP’s viability as an eco-friendly, innovative, and cost-effective alternative in sustainable geotechnical engineering. It also investigates the feasibility of using Waste Coffee Powder (WCP) as a sustainable additive for improving sandy clay soils.</p>