Performance of Black Cotton Soil Stabilized with Silica Sand and Lime for Use as Road Subgrade

Designing foundations, particularly highway pavements, on black cotton soil has consistently posed a delinquent for engineers, as structures supported by this type of black cotton soil are prone to unexpected cracking and settlement. The issue this study aims to solve is the lack of appropriate performance materials for use as road subgrade in regions with black cotton soil. This study aims to inspect if a mixture of silica sand and lime can be used to advance the mechanical properties of black cotton soil, thereby improving its performance for road subgrade construction. The initial step involves evaluating natural soil’s qualities using various tests such as Unconfined Compressive Strength (UCS), Atterberg limits, Californian Bearing Ratio (CBR), and Compaction tests. Subsequently, the soil sample is blended with silica sand in incremental amounts ranging from 0% to 12% of the soil sample’s dry weight at intervals of 2%. Through this experimentation, it was determined that the ideal amount of silica sand for treating the soil is 8%. At this content level, the corresponding values for UCS and soaked CBR were 181.23 kPa and 6.9%, respectively. The results obtained did not meet the targeted strength; hence, it was necessary to add some lime content in order to meet the targets. After adding lime in steps of 2%, the characteristics of targeted strengths were met at 2% inclusion of lime, and the corresponding soaked CBR and UCS values were 12.3 % and 188.39 kPa, respectively. These values were in line with the recommended standard for treated soil characteristics to be used in subgrade material. In conclusion, an optimal mixture of 8% silica sand and 2% lime is selected.