IMPROVEMENT OF CRUDE OIL–CONTAMINATED LATERITIC SOIL USING STEAM INJECTION AND PERIWINKLE SHELL ASH FOR ROAD SUBBASE APPLICATIONS

Abstract

Contamination from petroleum hydrocarbons poses a significant threat to soil and groundwater systems, thereby endangering ecosystems, human health, and socio-economic sustainability. This study evaluates the combined effectiveness of steam injection remediation and periwinkle shell ash (PSA) stabilization in improving the geotechnical properties of crude oil–contaminated lateritic soil for road subbase applications. Steam injection was applied at durations of 1 hour, 1 hour 30 minutes, 2 hours, and 2 hours 30 minutes. The remediated soil was subsequently stabilized with PSA at incremental additions of 4% up to 16%. Geotechnical tests were conducted in accordance with BS 1377. Results showed that steam injection achieved a maximum total petroleum hydrocarbon (TPH) removal efficiency of 75.89% at 1 hour 30 minutes, beyond which efficiency declined. Compaction results indicated that the untreated soil had Maximum Dry Density (MDD) values of 1.60 Mg/m³ for British Standard Light (BSL) and 1.75 Mg/m³ for British Standard Heavy (BSH), which increased to peak values of 1.69 Mg/m³ and 1.88 Mg/m³, respectively, after treatment. Optimum moisture content (OMC) increased with PSA content, reaching 16.56% for BSL and 14.65% for BSH at 12% PSA. The untreated soil recorded an unsoaked CBR of 19.3%, while peak values of 65.78% for BSL and 83.48% for BSH were obtained at 8% PSA with 1 hour 30 minutes of steam injection. Soaked CBR improved from 6.81% to 31.82% for BSL and 49.64% for BSH, satisfying Nigerian General Specifications for subbase materials. The study demonstrates that the combined use of steam injection and PSA provides a sustainable and effective method for improving crude oil contaminated lateritic soils for road subbase material.