Strength and Bearing Capacity of Cement Stabilized Clayey Sand Subgrade with Plastic Fines

Abstract 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 response of soils with different plasticity characteristics at practical binder dosages remains insufficiently understood. This study evaluated two coarse-grained subgrade soils with plastic fines, classified as clayey sand (SC) and clayey–silty sand (SC-SM) soils. Both soils were treated with 6% ordinary Portland cement (OPC) and evaluated using Atterberg limits, modified proctor compaction, unconfined compressive strength (UCS), and soaked California Bearing Ratio (CBR) tests after 7 days. Cement treatment marginally reduced the maximum dry density of both soils, whereas the optimum moisture content decreased for the SC soil and increased for the SC-SM soil. The plasticity index changed only slightly, from 12.8 to 14.2% for SC and from 21.8 to 22.2% for SC-SM. In contrast, the engineering performance improved substantially. The mean UCS increased from 0.390 to 1.993 MPa for SC and from 0.472 to 0.684 MPa for SC-SM. Similarly, soaked CBR increased from around 9–72% for SC and from 35 to 83% for SC-SM. These results indicate that soil plasticity has a greater impact on the amount of strength improvement under the same treatment conditions than changes in index properties. A supplementary artificial neural network (ANN) analysis satisfactorily represented the measured UCS and CBR responses within the experimental dataset, supporting its use as a limited-domain interpretive tool.