Effect of Lupine Hull Ash on Geotechnical Behavior of Weak Expansive Subgrade Soils

Several road sections have failed due to volume changes of expansive soils during moisture variation. While there are various common stabilization techniques, the use of agricultural byproducts in stabilization works can minimize costs and environmental effects when compared to ordinary stabilization methods. This paper discusses an experimental approach used to study the influence of lupine hull ash on expansive soil as a subgrade material. The laboratory results show that the expansive soils belong to A‐7‐5 and CH classes according to AASHTO and USCS, respectively. The expansive soil was mixed with varying concentrations of lupine hull ash, namely, 3%, 6%, 9%, and 12%. The plasticity index and free swell index were reduced by 68.19% and 62.67%, respectively, when treated with a 12% lupine hull ash concentration. The compaction test revealed a decrement of MDD and increment in OMC values as the percentage of the stabilizer material increased. Additionally, the UCS and CBR values increased significantly as the concentration of the expansive soil increased. The mineralogical analysis showed that the untreated soil is composed of 46.2% silica, 28.7% montmorillonite, and 25.1% kaolinite minerals. The SEM and XRD analysis proved the microstructural and mineralogical changes when the expansive soil is mixed with the optimum lupine hull ash concentration. While the CBR value of natural soil is unsuitable for subgrade material, mixing it with a 9% concentration of lupine hull ash ensures that the expansive soil complies with the standard as subgrade material. The experimental findings of this study emphasize the suitability of lupine hull ash for treating expansive soil encountered in rural road construction works.