Expansive soils present substantial challenges in civil engineering because they undergo volume fluctuations with changes in water content, mainly affected by the clay mineral montmorillonite. Nanotechnology has rapidly and widely improved, finding applications across all engineering fields. This study focused on enhancing soil engineering performance using lime alone and the impact of varying quantities of nanosilica with lime in the soil, focusing on engineering parameters like Atterberg limits, maximum dry density, optimum moisture content, and unconfined compressive strength over curing periods of 7, 14, and 28 days. In this study, the basic properties of soil were initially determined. Then, lime was mixed with soil in different proportions of 2%, 4%, 6%, and 8% according to the dry weight of the soil. Based on strength criteria, soil mixed with 4% lime gives the best results. Keeping the lime content constant at 4%, nanosilica was added to the soil. These findings suggest modifications in the amended soil's plasticity, compaction characteristics, and strength with the minor addition of nanosilica to lime-mixed black cotton soil. The enhancement in strength of expansive soils relies on the amount of lime and nanosilica and the duration of curing. After conducting tests, it was found that the optimal quantities for lime and nanosilica through strength performance tests are 4% and 3%, respectively. The research asserts that adding nanosilica to lime notably improves the mechanical properties of black cotton soil. Scanning electron microscopy and X-ray diffractometer analyses support these findings, revealing variations in the character and strength of the CSH phase over curing time. These conclusions offer wide-ranging relevance for projects seeking to enhance the engineering properties of soft soils. Practical Applications: Soil with 4% lime and 3% nanosilica gives good results, and the use of lime in soil stabilization contributes to the reduction of environmental pollution. The cost of nanosilica for real projects demands huge quantities. From an economic and commercial perspective, nanosilica liquid and lime are generally considered cost-effective for most practical applications. However, nanosilica with lime is recommended in areas where durability is important. Lime with soil is used to strengthen the soil in pavements and embankments; for example, when strengthening black cotton soil used for an embankment with a top width of 2 m, height of 6 m, side slope of 1:1, and length of 1 m, the volume is calculated as 48 m³. For soil +4% lime +3% nanosilica, the dry density is 17.1 kN/m³ and the moisture content is 14.9%. Considering this, the mass of the sample is obtained as 943 kN. Consequently, the required quantities are 38 kN (3,872 kg) lime, 28 kN (2,435 L) nanosilica liquid, and 877 kN (89,443 kg) of soil in its dry state. The cost of lime and nanosilica liquid depends on the location. [ABSTRACT FROM AUTHOR]