Investigation of a Proposed Four Storey Building Sites Using Geophysical and Laboratory Engineering Testing Methods in Lagos, Nigeria

The spate of engineering structures collapse in Lagos metropolis with its attendant loss of lives and properties has assumed an alarming proportion in recent times. Efforts to mitigate such incidence has necessitated an integrated geophysical and geotechnical investigation of a proposed four storey building sites with a view to determine the suitability of the site for the proposed project. Resistivity investigation, un-drained multi-stage triaxial compression and oedometer consolidation tests were carried out to determine the engineering properties of the subsurface. The results revealed peaty clay to silty sand materials characterized by 35kN/m 2 75kN/m 2 cohesion values, (5°-13°) internal friction, 29.3% 64.5% natural water content and 1.652 – 1.972 Mg/m 3 bulk density. The allowable bearing capacity of 50 kN/m 2 , volume compressibility from 0.115 m 2 /MN to 0.666 m 2 /MN, initial void ratio and consolidation coefficient of 0.779 1.381 and 2.7 m 2 /year 8.3 m 2 /year respectively on the pressure range of 0 to 400 kN/m 2 and estimated settlement values of 114 to 273 mm were obtained for the site materials. These results are indicative of soft to stiff clays and presence of sands and silts in the essentially clayey deposit. The study area is thus underlain by extensive zone of ductile and low strength founding materials having medium to high compressibility and settlement value that exceeds the tolerable limit suitable for founding a four storey building and should therefore be avoided. These characteristics preclude the use of conventional shallow foundations, piles or vibro-replacement up