Evaluation of Subsoil Competence for Foundation Design Design in Rumuokwuta, Port Harcourt, Eastern Niger Delta

Aim: A subsurface geotechnical investigation was carried out for the purpose of establishing the depth of competent soil for foundation design and construction of a one-storey building.

Study Design: The study was aimed at assessing the subsoil competence for a foundation design in the Eastern Niger Delta using engineering geology and geotechnics.

Place and Duration of Study: The research was conducted in three locations along the Rumuokwuta axis of Port Harcourt (the eastern Niger Delta) between April and September 2019.

Method: The study involved both field sampling and laboratory analysis. This involved soil boring for the retrieval of disturbed and relatively undisturbed samples for analysis, which involves grain size analysis, the Atterberg limits, moisture content, and unit weights. Also, Oedometer consolidation Oedometer and undrained, unconsolidated triaxial tests were carried out.

Results: The study revealed two main stratigraphic layers that are mostly fine within the shallow foundation level (0.0–3.0m). From the results, the soil exhibited the following geotechnical properties: liquid limit (41-46%), plastic limit (21-23%), plasticity index (18-24%), and moisture content range (20.6-24.7%). The undrained cohesion value is 55 kPa, and the average frictional angle is 5o. The coefficients of compression (Mv) and consolidation (Cv) were 0.20 m2 /MN and 40.7 m2/yr, respectively.

Conclusion: With the moderate bearing and settlement values within the shallow foundation level, the feasibility of adopting a shallow foundation for the purposed structure is tolerable. A shallow foundation (1.4m minimum) with an allowable bearing pressure of 100 kPa is therefore recommended.