Preliminary geological investigation into the causes of foundation failure in Jalingo, Northeast Nigeria

Abstract

Post-foundation study for the preliminary causes of cracks in buildings at the Central Bank 
of Nigeria (old site) Jalingo branch, Northeast Nigeria, was carried out using a geophysical 
approach and groundwater level monitoring. The geophysical survey method employed 
was the electrical resistivity method. Vertical electrical sounding (VES) was carried out 
using a Schlumberger electrode array with a maximum half current electrode separation 
of 20 m. The VES results revealed the presence of three geo-electric subsurface layers in 
the area, namely clayey sand, fractured/weathered basement, and crystalline basement. 
The resistivity of the clayey sand varies from 45 to 210 Ωm, while that of fractured/weath
ered basement varies from 305 to 5,858 Ωm and that of the crystalline basement varies 
from 1,000 to 10,075 Ωm, with corresponding thicknesses ranging from 0.5 to 2.3 m, 0.2 
to 6 m, and 2.6 to 4 m to an infinite depth, respectively. The study area’s field curves 
were analyzed; H- and Q-curve types were 35.7% and 64.3%, respectively. Iso-resistivity 
delineation at 0.5, 1.5, and 3 m showed that the region with high resistivity correspond
ing to the crystalline basement is found in the northeastern part of the study area and is 
most suitable for the foundation. The results show that the investigated building was sited 
within the incompetent clayey sand layer with resistivity generally less than 200 Ώm.