A foundation investigation was carried out at a proposed site for a residential building in Oda Town, Akure, Nigeria. The research is aimed at evaluating the competence of the sub-soil as foundation materials. Geophysical and geotechnical techniques were employed to characterise the subsurface foundation properties of the soil. A total of 8 Vertical Electrical Soundings and 6 disturbed soil samples were collected to aid the study. The geophysical results revealed three geo-electric sections, comprising the topsoil, weathered basement and rock head/basement. The topsoil is composed of compacted sandy-clay. The geo-electric sections further revealed the undulating nature of the rock head/basement. However, there is no evidence of faulting within the bedrock which can cause subsidence in the area. The geotechnical results revealed that the soil has a relatively low clay content. The soils within the study area are expected to exhibit low to medium swelling potential as deduced from the consistency tests. From these results, it can be conclusively stated that the subsoils within which the building or any engineering structure is to be founded are competent but generally, deeper foundations are recommended due to the prevailing H-curve across the vertical profiles for the soils examined.

The soils in Osinkan, Akure, were evaluated for the likely cause of foundation failure. Integrated geophysical and geotechnical methods was adopted. The data acquired from the geophysical survey was processed into field data pseudo-section and 2-D resistivity structure. The geotechnical analysis involved taking of undisturbed samples from two dug holes at the swampy area in the site of study. Empirical soil test was carried out to determine the grain size analysis, moisture content, Atterberg limit, specific gravity and shear strength. Three layers were delineated, the top soil, clayey sand and weathered basement. The resistivity of the top soil ranges from 2.7 ohm-m to 133.3 ohm-m with a depth ranging from 0.1m to 0.3m. The depth off weathered basement ranges from 0.3m to 0.5m. These variations in the soil resistivity influences corrosion risk, grounding design and overall foundation performances Likewise, the profiling variability indicates heterogeneous subsurface conditions, which may cause differential settlement. For foundation engineering purposes, the soil would require soil stabilisation and foundation design adjustment to ensure stability and durability The geotechnical analysis confirmed that the samples taken were a mixture of clay and sand. From the 2-D Resistivity structure, the depth to fresh basement is 12m. The foundation soil is failing due to the fact that the area is always water-logged after heavy down pour of rain. When the soil is wet the strength reduces and this should be the major cause of some buildings subsiding was authenticated from the geotechnical characteristics of the soils.