Due to the presence of potentially hazardous chemicals and minerals, the waste that is produced by thermal power plants poses a significant risk to the environment around it. This study is aimed to enhance the geotechnical characteristics of expansive soil by using bottom ash together with lime. The ultimate objective is to make the composite suitable for usage as a subgrade material. In the laboratory, a number of experiments, including consistency limits, compaction, unconfined compressive strength, permeability and California bearing ratio tests, were carried out on a variety of combinations of expansive soil and admixtures. The results of these tests were analyzed. As an outcome of the findings of the experimental testing, it was found that the geotechnical characteristics of expansive soil enhanced on introducing bottom ash alone and in combination with lime, therefore alleviating its disposal issue and making the environment healthier. According to the findings of the California bearing ratio study, if the optimum combination of bottom ash and lime may be employed effectively as a subgrade material, which would result in financial advantages.