Application of Scheffé for optimizing the California bearing ratio of soft soil reinforced with Lead‐Zinc mine tailings for low‐carbon pavement construction

This study investigates the potential of lead‐zinc mine tailings (LZMT) as an alternative stabilizing material for improving the bearing capacity of soil used in foundation and subgrade construction. A three‐component mixture design comprising Ikwo soil, LZMT, and water was developed using the Scheffé simplex lattice approach. The natural soil was initially characterized and classified as inorganic silt of low plasticity (A‐5, AASHTO), with a California Bearing Ratio (CBR) of approximately 4.10%, which is below the minimum 5% requirement specified by the Nigerian General Specifications for Roads and Bridges for subgrade materials. Laboratory CBR tests were conducted on the generated mixture proportions, and a second‐degree Scheffé polynomial model was developed to predict CBR response. The results showed that CBR values varied considerably with mixture composition, ranging from 4.60% at Y12 (soil–0.50, LZMT–0.25, water–0.25) to 6.06% at Y3 (soil–0.25, LZMT–0.50, water–0.25). The optimum mixture represented a 48% improvement over the natural soil and satisfied the specified subgrade requirement. Model validation demonstrated satisfactory predictive performance, with RMSE = 0.680, MAE = 0.615, and MAPE = 11.73%. Student's t ‐test and ANOVA conducted at a 95% confidence level further confirmed the statistical adequacy of the developed model. The findings demonstrate that LZMT can effectively enhance soil bearing capacity while providing a beneficial pathway for mine‐tailings utilization and supporting circular‐economy principles in sustainable geotechnical construction.