Development of compaction behaviour model for lead-contaminated kaolin clay under variable compactive efforts

Compaction behaviour significantly influences the performance and stability of earth structures, particularly when soils are subjected to chemical contamination that alters their engineering characteristics. Lead contamination, commonly associated with industrial and construction activities, can modify the physicochemical properties of clay and consequently affect its moisture–density relationship. However, limited systematic studies have evaluated the compaction behaviour of lead-contaminated kaolin clay under multiple compactive efforts within an integrated predictive modelling framework. This study aims to investigate the compaction behaviour of kaolin clay contaminated with 0–4000 mg/L lead nitrate under Reduced, Standard, and Modified Proctor Compaction energies, and to develop empirical models for predicting Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). Laboratory testing was conducted to determine physical properties including Atterberg limits, specific gravity, linear shrinkage, and pH, followed by controlled compaction testing at defined moisture states. The results indicate that increasing lead concentration leads to a moderate increase in moisture demand, while higher compactive effort reduces OMC and increases dry density. Observed variations in plasticity, shrinkage characteristics, and chemical environment were found to be associated with changes in compaction response. Based on statistical correlation and Multiple Linear Regression (MLR) analysis, empirical compaction behaviour models incorporating scaled lead concentration, scaled compactive effort, moisture condition, and dry density indicators were developed and independently validated, demonstrating strong predictive capability. The developed OMC model achieved a coefficient of determination (R2) of 98.77% during model development and 97.71% during validation, while the MDD model achieved corresponding R2 values of 95.31% and 93.84%, indicating excellent agreement between the predicted and measured values. The regression structure confirmed that both contamination level and compactive effort exert statistically significant influence on moisture demand for the OMC model. In contrast, the MDD model identified compactive effort as the dominant predictor with strong statistical significance, while lead concentration did not demonstrate a significant influence within the investigated range. Thus, indicate that density development is governed primarily by mechanical compactive energy rather than chemical modification. The developed models provide a practical approach for estimating compaction parameters of lead-contaminated kaolin clay and contribute to improved assessment of contaminated fine-grained soils in geotechnical engineering practice.