Innovative Analysis and Advanced Modeling of UCS and CBR in Fly Ash- and Cement-Treated Soils: Assessing the Influence of Chemical Oxides

Unconfined compressive strength (UCS) and California Bearing Ratio (CBR) are critical for assessing soil strength under vertical loading, especially in fine-grained soils, which often fail to meet the required standards for road and embankment projects. This study examines the effects of cement and fly ash on improving UCS and CBR through soil stabilization. The results showed an increase in both UCS and CBR with the incorporation of these materials, though the improvements were asymmetrical depending on the dosage of cement and fly ash. The variation is attributed to changes in the soil-cement or soil-fly ash matrix due to chemical oxides like silica, alumina, and calcium. The study modeled UCS and CBR using three mathematical models: pure quadratic (PQ), interaction (IA), and full quadratic (FQ), based on 130 fly ash-treated, 31 cement-treated, and 50 untreated soil datasets. The FQ model best predicted UCS (R 2 = 0.88) and CBR (R 2 = 0.95). Calcium oxide and curing time were the most influential factors for UCS while curing time and optimum moisture content were key for CBR. This study suggests a high-calcium oxide soil-additive matrix to enhance UCS and CBR in fine-grained soils.