Main Article Content
Geotechnical data were complemented with geophysical investigation and employed to delineate problematic soils in parts of Kosofe Lagos, Southwestern Nigeria. The study area was chosen because of known issues regarding cracking and differential settlement of infrastructures founded on soils in the area. The aim is to generate profiles and maps that show the spatial distribution of the problem soil to aid in foundation planning. Forty eight borehole logs and nine Vertical Electrical Soundings were compiled to delineate the different subsurface lithology which include peat, clay and sand. The results showed that the peat layer has maximum thickness of about 18.25 m but absent in some boreholes. This is underlain by clay unit with thickness ranging between 2.50-28.50 m. Sand unit constitute the third layer delineated with maximum thickness of 14m. There is a general thickening of peat soils in the northern parts, especially around the streams in the area which is instructive on the role of stream in the formation of the peat. The clay on the other hand is thickest around the northeastern and southeastern parts. The soil profiles generated reveal that the area is underlain with thick peat and clay having significant lateral, vertical variation and rapidly changing lithological facie. The extensive occurrence of these poor engineering soils calls for adequate engineering precaution in designs of building foundation.
Key word: VES, geotechnical borehole profiles, problem soils, foundation, southwestern Nigeria