Expansive Soil Treated with Circulating Fluidized Bed Ash Slag as Subgrade Fill: Engineering Performance Evaluation and Enhancement

Expansive soil undergoes significant changes in volume due to variations in water content, which can cause expansion and contraction. The microstructure of circulating fluidized bed ash slag (CFBAS) differs from other solid wastes, making it more environmentally friendly. This study aims to evaluate the impact of CFBAS on the physical and mechanical properties of expansive soils at different contents and curing times. The laboratory test results indicate that CFBAS can effectively improve the uniformity of the soil’s grain composition. The uniaxial compressive strength of the expansive soil was increased by 125%. With a CFBAS content of 5%, the soil becomes weakly expansive, but it becomes nonexpansive with a CFBAS content of more than 10%. Additionally, CFBAS significantly affects the deformation resistance and California bearing ratio of expansive soils. The improvement effect becomes more evident and stable over time. Based on the test results, economic considerations, and engineering requirements, it is recommended to use CFBAS with a dosage of 15% and a curing time of at least 28 days.