Strength and Bearing Capacity of Cement-Stabilized Subgrade Soils with Plastic Fines: Experimental Investigation and ANN Modeling

Subgrade soils containing plastic fines often exhibit low strength and high moisture sensitivity, limiting their direct use in pavement applications. While cement stabilization is widely adopted, the relationship between plasticity characteristics and strength development at practical binder dosages remains insufficiently clarified. This study evaluates the response of two subgrade soils (red and yellow) with contrasting plasticity characteristics to a representative 6% ordinary Portland cement (OPC) dosage. Laboratory testing included Atterberg limits, modified Proctor compaction, Unconfined Compressive Strength (UCS), and soaked California Bearing Ratio (CBR) after 7 days of curing. Cement treatment slightly increased optimum moisture content and marginally reduced maximum dry density, reflecting hydration-induced structural rearrangement. Plasticity indices changed only minimally (PI = 12.8→14.2 and 21.8→22.2), whereas mechanical improvements were substantial: UCS increased from 0.4 to 2.1 MPa and from 0.5 to 0.7 MPa, and soaked CBR increased from < 15% to ~ 80% for both soils. These findings indicate that strength enhancement is governed primarily by cementitious bonding rather than reductions in plasticity index, and that a moderate cement dosage can partially reduce the disparity in bearing capacity across soils with differing fines plasticity. An artificial neural network (ANN) model was further developed to estimate UCS and CBR within the investigated parameter range, achieving coefficients of determination (R² > 0.95). The results demonstrate the potential of integrating targeted laboratory testing with data-driven modeling for performance-based subgrade stabilization, while emphasizing that predictive applicability is confined to the tested material domain.