Sustainable Stabilization of Clay Soil Using Lime and Oryza sativa-Waste-Derived Dried Solid Digestate

Clay-rich soils are stabilized using fly ash, cement, lime, or solid waste with chemical activators to improve strength and reduce moisture-induced settlement. This study explores the stabilization of clay using lime and dried solid digestate (DSD) derived from food waste to improve its strength. A clay sample was treated with varying proportions of DSD (1–5%) along with 4.5% lime, by dry weight of soil. Samples were compacted at optimum moisture content and cured for periods of 0, 7, 14, and 28 days. The improvement in geotechnical behavior was assessed through Atterberg limits, unconfined compressive strength (UCS), and microscopic analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). Compared with untreated clay (62.03 kPa), the results show that adding 2% DSD and lime significantly increased compressive strength (446.5 kPa) and decreased plasticity by 69%. X-ray fluorescence (XRF) analysis revealed that the lime contained 81% of high calcium oxide (CaO), which supports pozzolanic and carbonation processes, whereas DSD served as a supplementary additive. Hence, the integration of DSD in soil stabilization offers a dual benefit: enhancing geotechnical performance and promoting environmental sustainability by diverting food waste from landfills and supporting circular resource use.