Multi-technique subsoil characterisation in the coastal environment of Lekki Peninsula, Lagos, southwest Nigeria

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ABSTRACT Integrated site investigations using VES techniques, SPT, borehole drilling, soil moisture content and specific gravity have been conducted at LFTZ, Lekki, Lagos, Nigeria. VES results correlated with borehole data revealed a lithological sequence with maximum five geoelectric layers. Inferred lithologies include low/moderate resistivity (45.6–206.3 Ωm) topsoil of sand/silty sand followed by a succession of silty sand/sand layers to a depth of about 45 m. Low depth silty sand (resistivity <300 Ωm) is the prevalent soil in the second and/or third strata and sand (resistivity >300 Ωm) is the last layer across the traverses. SPT results correlate well with borehole data showing a subsurface lithological sequence of very loose/loose grading silty sand, loose/medium dense grading silty sand, medium dense/dense grading sand and dense grading sand. Soil density Increases downward in boreholes with SPT N-values (2–24). Grain size distribution curves depict uniformly graded/narrowly graded soil aggregates with Cu and Cc in the ranges 1.33–8.00 and 0.610–2.00, respectively. Moderate moisture content values (16.72–27.82) suggest that the water table is close to the surface toward the nearby Atlantic Ocean. Specific gravity values (2.60–2.78) lie within the range for most soils and indicate that salinity is minimal at the study location.