Index Properties and Compaction Characteristics of Vermiremediated Crude Oil-Contaminated Lateritic Soil Stabilized with Gum Arabic for Road Subgrade Application

Abstract

Crude oil contamination progressively degrades the index and compaction properties of lateritic soils, undermining their suitability as pavement subgrade material. This study evaluates the index properties and compaction characteristics of vermiremediated crude oil-contaminated lateritic soil stabilized with Gum Arabic (GA), a natural biopolymer, as a sustainable alternative to conventional chemical stabilizers. Lateritic soil obtained from Shika, Zaria, Kaduna State, was contaminated with Bonny Light crude oil at 75 cl per 10 kg of soil, biologically treated using the earthworm species Eudrilus eugeniae, and thereafter stabilized with 0, 2, 4, 6 and 8% GA by dry weight. Natural moisture content, specific gravity, Atterberg limits, particle size distribution, linear shrinkage, and compaction characteristics (maximum dry density, MDD, and optimum moisture content, OMC) were determined for the British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH) compactive efforts, in accordance with BS 1377 (1990). Contamination increased the liquid limit from 47.0% to 51.8% and reduced the specific gravity from 2.66 to 2.40. Following vermiremediation and GA stabilization, the liquid limit and plastic limit generally decreased with increasing GA content, falling from 54.0% and 32.3% at 0% GA to minimum values of 44.0% and 15.0% at 6% GA, respectively, while the percentage fines passing the 0.075 mm sieve decreased markedly, indicating particle flocculation and agglomeration. The MDD values were most sensitive to GA addition under the BSH effort, decreasing from 1.79 g/cm³ at 0% GA to 1.70 g/cm³ at 6% GA, while OMC values generally increased with GA content before declining at 8% GA. The results demonstrate that GA measurably alters the index and compactive behaviour of remediated contaminated lateritic soil, with 2-4% GA offering the most favourable balance of reduced plasticity and workable compaction response for subgrade application.