Electrokinetic–Adsorptive Remediation of Hydrocarbon-Contaminated Soil: Trade-Offs Between Strength, Durability and Fabric Evolution

Abstract

Electrokinetic remediation (EKR) is a promising technique for treating hydrocarbon contaminated soils; however, its implications for soil engineering behaviour are not fully understood. This study investigates the combined effects of electrokinetic transport and carbon-based permeable reactive barriers (charcoal and activated carbon) on contaminant removal, soil fabric evolution, and geotechnical performance. Crude oil contaminated soil with an initial total petroleum hydrocarbon (TPH) concentration of 78,600 mg/kg was treated under an electric gradient of 1 V/cm. Removal efficiencies of 81.4% and 84.6% were achieved for charcoal and activated carbon, respectively, with the latter showing faster remediation. Significant improvements were observed in compaction characteristics and bearing capacity, with California Bearing Ratio (CBR) increasing from 6.7% to 35.9–46.1%. However, remediation resulted in increased plasticity and very low durability under wet–dry cycling, indicating high susceptibility to moisture-induced degradation. These changes are attributed to removal of hydrocarbon coatings and subsequent particle aggregation, leading to reorganisation of soil fabric and enhanced soil–water interaction. The results reveal a fundamental trade off between contaminant removal and engineering performance: while electrokinetic remediation improves short term strength, it simultaneously increases plasticity and reduces durability. The findings highlight the need for post treatment stabilisation to render remediated soils suitable for structural applications.