GEOTECHNICAL CHARACTERIZATION AND SUITABILITY OF WEAK SOILS FOR SUSTAINABLE STABILIZATION IN RUKPOKWU, RIVERS STATE, NIGERIA

Abstract

Weak, moisture-sensitive soils in deltaic environments present major constraints to safe and durable infrastructure. This study provides a comprehensive geotechnical characterization of natural (untreated) soil from Rukpokwu, Obio/Akpor LGA, Rivers State, Nigeria, to assess its engineering suitability and establish a baseline for potential improvement. Representative samples were collected from the subgrade horizon (≈1.0 m) and tested in the laboratory according to BS 1377 procedures for Natural Moisture Content (NMC), Specific Gravity (Gs), Particle Size Distribution (PSD), Atterberg Limits (Liquid Limit [LL], Plastic Limit [PL], and Plasticity Index [PI]), and Standard Proctor Compaction to determine Maximum Dry Density (MDD) and Optimum Moisture Content (OMC), as well as California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS). Results show a mean natural moisture content of ~18.0%, specific gravity between 2.63 and 2.70, and a predominantly fine-grained matrix dominated by silt and clay. Index tests returned LL ≈ 38%, PL ≈ 17%, and PI ≈ 21%, classifying the soil as a highly plastic clay with significant shrink–swell potential. Compaction tests yielded an MDD of approximately 1.72 g/cm³ at an OMC of about 14.2%. Strength indicators were poor, with a CBR of roughly 3.99% and a UCS of about 433 kPa. Collectively, these findings demonstrate that the natural soil is moisture-sensitive, highly plastic, poorly graded, and of low bearing capacity, unsuitable for direct use as pavement subgrade, shallow foundation support, embankment fill, or backfill without treatment. The study concludes that stabilization is necessary and highlights the potential of sustainable pozzolanic additives from agricultural waste as viable options for improving the soil’s engineering performance.