Predicting subgrade soil Modulus of Resilience in Benin City, Nigeria

Abstract

The quality of subgrade soil is known to significantly affects pavement durability, with the modulus of resilience, measured by tests such as the California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS), being crucial for predicting soil resilience. Accurate estimation ensures cost-effective pavement design tailored to Benin City's conditions. Disturbed soil samples from selected regions in Benin City, were analysed for moisture content, specific gravity, particle size distribution, and Atterberg's Limits, and underwent CBR and UCS tests. Following British Standards, the modulus of resilience was calculated, and a regression model using CBR and UCS predicted resilience, validated with 30% of the data using R-squared, SSE, and RMSE metrics. Specific gravity ranged from 2.592 to 2.865, indicating silty soil with inorganic clay, while particle size distribution and Atterberg limits classified the soil as clay with intermediate plasticity. CBR values ranged from 4.76% to 15.27%, and UCS from 74.13 to 89.41 kN/m², classifying the soil from soft to stiff clay. The model, with a CBR exponent of 1 and UCS exponent of 2, showed an SSE of 0.9288, R-squared of 0.7404, adjusted R-squared of 0.7276, and RMSE of 0.1071, with a validation goodness of fit of 0.6768, indicating a strong predictive relationship.