Geotechnical Characterization of Soils in Ahoada Town, Rivers State for Safe Foundation Design and Construction (Published)
A geotechnical investigation was conducted to evaluate the subsurface conditions and assess the suitability of soils for shallow foundation construction in Ahoada town, Rivers State, Nigeria. The study involved field sampling and laboratory testing of soil samples to determine relevant geotechnical parameters such as grain size distribution, Atterberg limits, moisture content, and shear strength characteristics. The geological setting of the area is typical of the Niger Delta sedimentary basin, characterized by alternating layers of sand, silt, and clay deposits. Results show that the near-surface soils consist predominantly of clayey sand and sandy clay layers underlain by more competent sandy strata at greater depths. Results obtained show that the Atterberg limit results reveal that the liquid limit ranges from 53.5% to 97.8%, the plastic limit ranges from 30.1% to 60.0% while the plasticity index values range from 17.1% to 39.5%. The cohesive soils (clays) are highly plastic (CH) in the Unified Soil Classification System (USCS) designation. The natural moisture content ranges from 71.3% to 97.5%. The particle size distribution analysis reveals that the sand is fine to medium to coarse grained and in a medium dense state of compaction and based on its coefficient of uniformity and gradation classifies as poorly graded (SP) by the USCS designation. The moisture content of the sand ranges from 8.9% to 13.0% while the bulk unit weight ranges from 19.6KN/m3 to 20.3 KN/m3. The angle of shearing resistance ranges from 260 to 330. The result of the undrained shear strength of the clay ranges from 16Kpa and 19Kpa. The clay is very soft to soft and exhibit medium to high moisture content. The strength test result indicates a material of low undrained shear strength, the coefficient of consolidation, Cv of the clay soil samples varies between 1.40m2/year and 2.69 m2/year. The coefficient of volume compressibility, Mv, for the same materials varies between 0.215 m2/MN and 0.657 m2/MN, generally indicating clay layers of high to very high compressibility. The high groundwater table and presence of compressible clay layers in the upper strata pose challenges for shallow foundation design. However, with proper foundation design, including soil improvement or adequate footing depth, shallow foundations can be safely adopted in areas with adequate bearing capacity.
Keywords: Groundwater, foundation design, geotechnical characterization, soil stability