This study investigates the effectiveness of river silt and pond ash as sustainable stabilizing materials for improving the engineering properties of black cotton soil. The experimental program was carried out by incorporating river silt and pond ash in varying proportions of 0%, 2.5%, 5%, 7.5%, 10%, 12.5%, and 15% each, resulting in total additive contents of 0%, 5%, 10%, 15%, 20%, 25%, and 30% by dry weight of soil. Laboratory investigations were conducted to evaluate the changes in the plasticity characteristics and overall engineering behavior of the stabilized soil. The results of the plasticity index test indicate that the untreated black cotton soil has a high plasticity index of 35.51%. With increasing proportions of river silt and pond ash, the plasticity index generally decreases, reaching 21.22% at 30% total additive content. A significant reduction in plasticity is observed particularly at 25% and 30% replacement, indicating a reduction in the plastic and expansive characteristics of the soil. The improvement is attributed to the incorporation of relatively non-plastic materials, which modifies the soil particle interaction and reduces its moisture sensitivity. The findings demonstrate that the combined utilization of river silt and pond ash can effectively reduce the plasticity of black cotton soil and improve its suitability for ground improvement applications. The study also highlights the potential of utilizing locally available waste and marginal materials as sustainable alternatives to conventional soil stabilization practices.

Keywords: Black Cotton Soil; River Silt; Pond Ash; Soil Stabilization; Plasticity Index; Expansive Soil; Ground Improvement; Sustainable Construction.