Geotechnical Indications and Shallow Bearing Capacity Analysis within Lekki Peninsula, Lagos using Direct Shear Analysis

It has become imperative for a review of the subsurface engineering properties of the Lekki Peninsula due to increase in urbanization. The study focuses on the shear strength parameters and ultimately the shallow bearing capacity of the subsoil using the direct shear method. With methods based on CPT, SPT, Particle Size Distribution and Direct Shear Analysis, an underlying loosed sandy layer of about 4m thick overlying a medium dense sand was revealed. Plot from direct shear analysis reveals zero cohesion and phi values = 170 indicative of a loosed soil. This loosed property of the soil was also revealed by the non-peaked plot of the direct shear test and the particle size distribution plot. Based on correlation for non-cohesive soils using N-values, compressibility parameters for the loosed sandy layer (N values=5) indicates Elastic Modulus < 3500Kpa, while the Medium dense sandy layer (N values=17) indicates values of about 13000Kpa. This implies high compressibility is expected within the loosed sandy layer. Settlement predictions based on a loading of 200KN/m² indicated a settlement of 74mm. Recorded Water level is less than 1m. Based on a shallow bearing capacity of 55kpa and intolerable settlements and CPT values within the study area, a raft foundation is most appropriate for multistory building while a deep foundation is apt for higher loads.

Keywords:Subsoil; Geotechnical; Bearing capacity; Foundation; Design; Lekki penninsula; Lagos