Index Properties, and Compaction Characteristics of Palm Kernel Shell Ash-Stabilized Vermi-remediated Crude Oil-Contaminated Lateritic Soil for Highway Sub-Base Application

John E. Sani, Daniel O. Oyeleke, George Moses

Abstract


Crude oil spillage progressively degrades the geotechnical performance of lateritic soils used in highway construction, necessitating remediation before reuse as pavement material. This study evaluated the remediation efficiency, index properties, and compaction characteristics of Palm Kernel Shell Ash (PKSA)-stabilized, Vermi-remediated, crude-oil-contaminated lateritic soil intended for highway sub-base application. Lateritic soil obtained from Shika, Zaria, Kaduna State, Nigeria was contaminated with crude oil at 150 cl per 20 kg of soil and subsequently treated using the earthworm species Eudrilus eugeniae at 200 worms per 100 kg of soil for 30 days. Vermi-remediation reduced the total petroleum hydrocarbon (TPH) content from 4500 mg/kg to an average of 3300 mg/kg, corresponding to a remediation efficiency of about 26%. The Vermi-remediated soil was thereafter stabilized with PKSA at 0, 4, 8, 12 and 16% by dry weight and evaluated for index, compaction, and strength properties in accordance with BS 1377 (1990). The liquid limit, plastic limit and plasticity index of the Vermi-remediated soil (54.0%, 32.3% and 21.7%) varied irregularly with PKSA content, while linear shrinkage remained close to 11% throughout. Specific gravity decreased marginally from 2.4 to 2.2 with increasing PKSA content, consistent with the lower density of the ash. Compaction results showed that maximum dry density (MDD) decreased under British Standard Light (BSL) and West African Standard (WAS) efforts but increased under British Standard Heavy (BSH) compaction, while optimum moisture content (OMC) generally increased with PKSA content across all compactive efforts. The findings support the use of Vermi-remediation combined with agricultural-waste-ash stabilization as a sustainable, low-cost technique for rehabilitating petroleum-impacted lateritic soils for highway earthworks in Nigeria. 


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