Local Geology, Shear Strength Properties and Bearing Capacity of Coastal Plain Sands in Uyo Metropolis, Akwa-Ibom State, Southeastern Nigeria

Abstract

The Bearing capacity of the soil within Uyo metropolis in South-Eastern State of Akwa Ibom was investigated in this study. The soil belongs to Coastal Plain Sand often called the Benin Formation in the geology of Niger Delta. Both Field and Laboratory methods were employed in the study. The field method consisted of Cone Penetration Test (CPT) with a 2.5 ton Dutch Guada cone penetrometer, and the Light weight penetrometer LRS 10. For the CPT, depth of investigation was refusal depth which varies from about 9.0 m to 20.0 m. The depth of investigation by the LRS 10 was not more than 6.0 m. The direct parameter the LRS 10 evaluates is the relative density. Soil sounding with the LRS 10 indicated for all the sites a ‘loose to medium’ consistency. No dense or very dense stratum was encountered. The Laboratory method employed was the Direct shear box tests This was used to determine the cohesive property and angle of shearing resistance of the soil, that is the C- ∅ property. The cohesion varies very widely; with a value ranging from a zero value to 54 kN/m2. The angle of shearing resistance ranges from 8º to 30.7º, with more than ninety percent falling below 28º, indicating a highly compressible soil that is prone to local shear failure. Ultimate bearing capacities are as low as 100.93 kN/m2 and as high as 571.1 kN/m2. Settlement associated with safe bearing pressure estimated from CPT data ranged from 0.35 cm to 3.89 cm. while that from laboratory gives lesser values, thereby making that from the field value conservative.