Engineering Geological Investigation of Shallow Foundation Conditions in Amasoma, Bayelsa State, Nigeria (Published)
An engineering geological investigation was conducted to evaluate the suitability of subsoil conditions for shallow foundation systems in Amasoma, Bayelsa State. The study focused on characterizing the near-surface soils, determining their geotechnical properties, and assessing their bearing capacity and settlement characteristics for safe and economical foundation design within the Niger Delta depositional environment. Laboratory results indicate that soils are predominantly soft to firm silty clay and clayey silt with intercalations of sandy layers. The Atterberg limit results reveal that the liquid limit ranges from 46.5% to 98.3%, the plastic limit ranges from 26.7% to 49.8% while the plasticity index values range from 23.0% to 48.5%. The cohesive soils (clays) are highly plastic (CH) in the Unified Soil Classification System (USCS) designation. The natural moisture content ranges from 39.8% to 91.3%. 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, suggesting moderate shear strength characteristics. 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 1.13m2/year and 2.87 m2/year. The coefficient of volume compressibility, Mv, for the same materials varies between 0.23 m2/MN and 0.833 m2/MN, generally indicating clay layers of high to very high compressibility. Raft foundation is best suited for these weak, soft foundation materials for lightly loaded buildings with proper soil improvement.
Keywords: Atterberg limit, Geotechnical Properties, Particle Size, compressibility
Engineering Geological Properties of Subsurface Soils for Foundation Purposes in Parts of Bayelsa State, Niger Delta (Published)
The geotechnical properties of soil samples obtained from eight (8) boreholes from some parts of Bayelsa State were determined to assess their suitability as foundation materials. The geotechnical characteristics of the soils were determined from the laboratory and field works. The Atterberg limit results reveal that the liquid limit ranges from 46.5% to 98.3%, the plastic limit ranges from 23.5% to 56.3% while the plasticity Index values range from 17.1% to 51.3%. The clays are highly plastic (CH) in the USCS designation. The natural moisture content ranges from 35.9% to 91.3%, the moisture content is relatively high, this could be attributed to the wet season period of sampling. The particle size analysis disclosed that the cohesionless samples are predominantly fine to medium and medium dense sands. The triaxial test results shows that values of Cohesion (C) ranges between 16 – 40KN/m2 and the friction angle (ϕ) ranges between 3 – 6o. The result of the undrained shear strength of the clay ranges between 20Kpa and 24Kpa. The coefficient of consolidation (Cv) of the clay soil samples varies between 1.13 m2/yr and 2.89 m2/yr, the coefficient of volume compressibility, (Mv) for these same materials varies between 0.215 m2/MN and 6.338 m2/MN. Generally, indicating clay layers of high to very high compressibility. The calculated values for ultimate bearing capacity (qu) and allowable bearing capacity (qa) varies between 100.29KN/m2 to 151.49 KN/m2 and 33.42 KN/m2 to 50.50 KN/m2 respectively. The analyses showed that the values of ultimate bearing capacity increases with depth. The calculated settlement ranges between 69mm to 653mm with the thickness of clay of 7.5m and 30.0m respectively. Raft foundation is best suited for these weak, soft foundation materials for light structural loads but for heavy structural load, a pile foundation is recommended.
Keywords: Atterberg limit, coefficient of consolidation, coefficient of volume compressibility, cohesion, friction angle, shear strength