GEOTECHNICAL INSIGHTS ON SHALLOW FOUNDATIONS IN SEDIMENTARY TERRAINS: FINDINGS FROM BONNY ISLAND

Abstract

This study investigated the Geotechnical assessment of shallow foundation in sedimentary deposits. The samples were taken by drilling with the aid of percussion drilling rig to the maximum depth of 2m, and were further subjected to various laboratory analysis. According to the findings, the lithographic sequence consists of fine sand to dense sand. The soil has a moisture content of 17.5-18.8%, the particle size distribution analysis showed poorly graded sand. Values of the undrained cohesion is 0 kPa showing cohesionless nature of the soil and angle of internal friction are between 32º to 33º indicating good shear strength properties. Bearing capacity for the homogenous subgrade ranged from the top soil to 1 m depth below the top soil, 218 kN/m2 to 753 kN/m2, and to 2m depth below 1m it ranges from 427 kN/m2 to 1064 kN/m2, this suggested very adequate strength for load bearing structures. Based on the assessment, a shallow foundation with a depth of 1or 1.5 meter is recommended within the allowable bearing pressure stated above. A shallow foundation with a spread footing or mat foundation is suitable for this site, the spread footing can transfer the load to the required depth, while the mat foundation can distribute the load over a larger area, reducing the pressure on the soil.