Geotechnical Characterization and Rice Husk Ash Stabilization of Vermiremediated Crude Oil–Contaminated Lateritic Soil for Highway Applications

John E. Sani, Alabi O. Gideon, George Moses

Abstract


Crude oil contamination severely degrades the index, compaction, and strength properties of lateritic soils in Nigeria's oil-producing regions, limiting their suitability for road construction. This study evaluated the geotechnical response of crude oil–contaminated lateritic soil to sequential treatment by vermiremediation and rice husk ash (RHA) stabilization. Lateritic soil sourced from Shika, Zaria, Kaduna State (11°15′ N, 7°45′ E) was artificially contaminated with crude oil at 75 cl per 10 kg of soil and subsequently vermiremediated using the earthworm Eudrilus eugeniae at a rate equivalent to 300 worms per 200 kg of soil over 30 days, achieving a total petroleum hydrocarbon (TPH) reduction of approximately 27%. The vermiremediated soil was then stabilized with RHA at 0, 4, 8, 12, and 16% by dry weight and evaluated in accordance with BS 1377 (1990) and BS 1924 (1990) using index, compaction (British Standard Light [BSL], West African Standard [WAS], and British Standard Heavy [BSH] efforts), unconfined compressive strength (UCS), California bearing ratio (CBR), and durability tests. Untreated vermiremediated soil classified as A-7-6 (CL) with a plasticity index of 19.5% and unsoaked CBR values below 9% for all compactive efforts, confirming its unsuitability as a pavement material. RHA stabilization increased CBR values to a maximum of 26–32% and produced peak 28-day UCS gains of up to 227.7 kN/m² for the WAS effort at 16% RHA, although the optimum RHA content varied with compactive effort (8% for BSL, 16% for WAS and BSH). The results indicate that RHA is a viable, low-cost pozzolanic stabilizer capable of restoring vermiremediated, oil-impacted lateritic soil to a condition suitable for subgrade and light sub-base applications, although values generally remained below the 80% CBR threshold specified for base-course material by the Nigerian General Specifications for Roads and Bridges (2016). 


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References


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