Sustainable stabilization of expansive soil using fly ash, olive cake ash, and zeolite mixtures: A comparative experimental study with plaxis modeling

Abstract

In this study, the effectiveness of fly ash (FA), olive cake ash (OCA), and zeolite in stabilizing expansive soil was investigated, focusing on their impact on swelling and strength properties. The research involved the use of an artificial expansive soil mixture composed of 85% kaolinite and 15% bentonite. Seventeen distinct samples were prepared, incorporating varying percentages of FA (5% to 20%), zeolite (5% to 20%), and OCA (2.5% to 10%), along with combinations of FA with OCA and zeolite. The aim was to identify the optimal proportions of these additives for enhancing soil stability, particularly in terms of swelling behavior and mechanical strength. The experimental program included a series of tests to evaluate the strength characteristics of both untreated and treated soils. Key tests such as unconfined compressive strength (UCS), California Bearing Ratio (CBR), and direct shear tests were performed. Additionally, consolidation and free swell tests were conducted to assess the impact of the additives on the soil's compressibility and swelling potential. The study also involved standard compaction tests, Atterberg limits, grain size distribution, specific gravity tests, XRF, and SEM analyses to provide a comprehensive understanding of the soil behavior. The results showed that adding 20% FA significantly improved the UCS of the soil, making it the most effective percentage for enhancing strength. OCA provided moderate strength gains at lower percentages, with 2.5% being the optimal amount. These gains became more pronounced after 28 days of curing due to OCA's slow pozzolanic reaction. The combination of FA and OCA produced the highest strength after curing, demonstrating strong synergistic effects. Zeolite also enhanced UCS, particularly at 15%, due to its cement-like properties.