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
Geotechnical Considerations for Foundation Design in Parts of Yenagoa, Bayelsa State, Niger Delta Nigeria (Published)
This research was to determine geotechnical properties of the subsoils in some part of Yenagoa and environs to obtain proper foundation design parameters, six towns in Yenagoa local government area, Bayelsa state was investigated. Six geotechnical boreholes was drilled and laboratory studies of soils samples were obtained from 0-20.25m deep. Subsurface soil profiles were delineated followed by determination of their index and mechanical properties, including Atterberg limits, particle sizes distribution, undrained shear strength, shear box test and consolidation coefficient. The general soil profile consists of (from top to bottom), , upper Silty clay horizon (0.0-5.25m thickness) soft to firm for Yenagoa study areas, Medium silty clay horizon (0.75 to 1.5m thickness) soft to firm Yenagoa study areas, low clayey sand horizon (0.75 to 1.5m thickness) soft Yenagoa study areas, peaty clay (1.0m thickness between 3.0-4.0m) soft Igbogene Yenagoa, upper sand horizon (3.0m thickness) silty sand Etegwe town Yenagoa, lower sand horizon (13.5 to 18.0m) silty sand to fine to medium and medium coarse appear in all the boreholes in Yenagoa. Yenagoa sub-soil show clay of high plasticity, silt of intermediate to high plasticity (CH, MI and MH) according to unified soil classification system from the results it shows that pad foundation is more economical in the study areas. Raft foundation is more economical in the six towns study areas of Yenagoa with Allowable bearing capacity of the upper clay layer ranges from 23-128KN/m2 In view of the significant variations in the stratification and engineering geological index properties of the soil in the six towns in Yenagoa while geotechnical data of one location cannot be used as a basis for design of foundation in a nearby land. Axial load carrying capacity for 305, 306mm, 356, 360mm, 406mm, 600and 610mm diameter for bore pile and tubular driven steel cased piles respectively were calculated for all the studies areas. Where high rise building is required in the various study areas. The study shows that the frequent causes of building collapse in Yenagoa are as a result of inadequate geotechnical investigations of the subsoil, poor quality materials, and poor work supervision.
Keywords: Bayelsa State, Niger-Delta, Yenagoa, foundation design, geotechnical consideration