Geotechnical Performance of Agbede Soil Stabilized with Groundnut Shell Ash (GSA): Index Properties, Compaction Characteristics, and Strength Behavior

Abstract

Expansive soils in Nigeria are often unsuitable for construction due to high plasticity, volumetric instability, and poor load-bearing capacity. Conventional stabilizers such as cement and lime, although effective, are costly and environmentally unsustainable. This study investigates the geotechnical performance of Agbede soil stabilized with groundnut shell ash (GSA), emphasizing index properties, compaction characteristics, and strength behavior.

Laboratory tests conducted in accordance with BS 1377 (1990) included particle size distribution, Atterberg limits, specific gravity, Standard Proctor compaction, California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), and Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX). Results showed that untreated Agbede soil was classified as highly plastic clay, with a plasticity index (PI) of 32% and maximum dry density (MDD) of 1.85 g/cm³.

Incorporation of GSA reduced PI to 14% at 15% GSA and improved MDD to 1.92 g/cm³ at 10% GSA, while optimum moisture content (OMC) decreased from 14.3% to 13.5%. Strength properties also improved markedly, with CBR increasing from 7% (untreated) to 21% at 15% GSA and UCS rising from 120 kN/m² to 280 kN/m². The findings establish GSA as a sustainable, cost-effective stabilizer suitable for subgrades and other geotechnical applications, while simultaneously supporting agricultural waste management.