Document Type : Research Paper
Abstract
This study investigated the relationship between coefficient of uniformity (Cu) and compaction indices of sandy subbase layers Bayelsa State, Nigeria, situated between longitude 6°15'E to 6°23'E and latitude 4°46'N to 5°51'N. Sandy subbase materials are widely used in pavement construction, yet the specific influence of Cu on compaction behavior remains inadequately understood, leading to suboptimal compaction practices and premature pavement failures. The objective was to establish quantitative relationships between Cu and maximum dry density (MDD) through empirical analysis. Nine sandy soil samples were collected from three zones (Yenagoa Swali, Amassoma, and Yenagoa Oxbow Lake) at depths of 0.5-1.0 meters. Laboratory testing following ASTM D422 and ASTM D698 standards included sieve analysis and Standard Proctor compaction tests. Statistical analysis employed Pearson correlation and polynomial regression modeling. Results revealed Cu values ranging from 2.36 to 3.04, with corresponding MDD values between 1618.8 and 1711.7 kg/m³. Well-graded soils (Cu > 2.8) achieved 4.1% higher MDD than poorly graded soils. Polynomial regression demonstrated strong predictive capability (R² = 0.89) following MDD = -226.06Cu² + 1330.4Cu - 251.31. Optimal compaction efficiency occurred at Cu: 2.85-3.05, fines content: 15-25%, and fineness modulus: 2.8-3.2. The study concludes that Cu significantly influences sandy subbase compaction behavior. Engineers should prioritize materials within identified optimal gradation ranges and adopt the developed predictive models for quality control in Niger Delta pavement construction projects.
