Effect of fly ash layer addition on the bearing capacity of expansive soil

The long-term structural performance of roads is mainly governed by the characteristics of subgrade soil. Subgrades with highly compressive clays are one of the challenging aspects worldwide. Expansive soils swell and shrink due to moisture variations. Such variations cause serious structural failures, commercial losses and fatalities worldwide. One of the most effective and economical methods for improving the engineering behaviour of expansive soil is the addition of stabilising agents such as lime or fly ash (FA) to expansive soil. In this study, a highly plastic black cotton soil (BCS) was stabilised using FA. Laboratory experiments and model tests were performed to determine the geoengineering properties and to study the strength behaviour of virgin clay soil and clay soil treated with FA. The experimental investigations indicated a decrease in the plasticity index and free swell index of BCS–FA mixes with an increase in FA content. Moreover, an increase in the California bearing ratio of the BCS–FA mix and layered BCS–FA composite was observed. Further, bearing capacity tests were performed on subgrades prepared with BCS–FA layers and BCS–FA mix with up to 40% FA content. The detailed methodology adopted for theoretical and experimental investigations is presented, and the obtained results are critically evaluated.