Geophysical Investigation of Subsurface Characteristics in Parts of Niger Delta Basin and its Geo-technical Implications: A Case Study of Amuzi-Obowo Area of Imo State, Southern Nigeria.

Abstract

The geophysical investigation of the subsurface characteristics in the Amuzi-Obowo area of Imo state, implored the use of the Vertical Electrical Sounding technique of the electrical resistivity method that revealed the existence of seven geoelectric layers with resistivity ranging from 14.2 Ωm (the 3rd layer of VES 12 ) to 240,000 Ωm (the 7th layer of VES 3).; Results show that the topsoils are made up of six-layer deposits consisting of fine-grained sand, medium-grained sand, coarse-grained sand, silt, clayey-silt and clay layer deposits with a range of resistivity of 36.6 Ωm (VES 8 ) to 3,321 Ωm (VES 3). The near-surface layer underneath the topsoil consists essentially of sandstone, fine-grained sand, medium-grained sand, coarse-grained sand, and silt. The depth to the layer ranges from 8m (VES 2) to 2.93m (VES 10), with thickness ranging from 0.14 to 2.46m. The incessant cracking of walls of buildings and falling of electric poles in some parts of the study area have been attributed to the nature of the low-resistivity units deduced as clay deposits underlying some of the very thin 2nd (near-surface) layers. Locations for only the construction of small structures were highlighted, and the locations not suitable for small structures were highlighted. It was concluded that medium to massive engineering structures can be placed anywhere in the study area except at the location of VES 2 , but for massive structures, the locations of VES 2, 5 ,8 10, 11 and 12 should be given further engineering considerations because of the relatively shallow depth of the underlying clay layers.