Black cotton soil is a typical swelling soil, which loses its strength when it comes under contact with water thereby increasing its volume. Likewise, in an absence of water, it shows multiple cracks resulting in shrinkage. This volumetric change causes distress to the structure located in the areas containing expansive soils and leads to structural failure. Therefore, the proposed study aimed at developing a stabilized black cotton soil surface for the construction of RESA (Runway End Safety Area) with a California bearing ratio (CBR) value greater than 15%. Prosopis juliflora ash was used as an additive in stabilizing the expansive soil. The ash contents were added in different percentages such as 0%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, and 4% by weight of the soil. The characteristics of the ash-treated soil were tested under three criteria such as gradation, physical parameters, and strength characteristics. Gradation includes wet sieve analysis, physical parameters include field density, swell index, Atterberg’s limit, modified proctor compaction, specific gravity, moisture content, and strength characteristics including California bearing ratio (CBR) and unconfined compressive strength. The targeted CBR value of more than 15% was achieved when 3.5% of ash content was added.