Geophysical and Geotechnical Investigation of Building’s Foundation around Crusher area, Lokoja, Kogi state, Nigeria
Authors: Abdulbariu Ibrahim  , Sarah Mercy Ebere Eze  , Mu’awiya Baba Aminu  , Ayinla Habeeb Ayoola  , Musa Ojochenemi Kizito  , Adedolapo Olujuwon Adegbite  , Mojeed Olaniyi Fasasi  , Ibrahim Olanrewaju Ibrahim  
Published: July 2024

Integration of geophysical and geotechnical techniques had been utilised to investigate the foundation of a site characterised with building cracks. It was conducted at Muhammadu Buhari Estate, Crusher area in Lokoja, Nigeria, The study aims to delineate geological features responsible for the failure of the building through 2-D resistivity imaging and electromagnetic surveys in conjunction with geotechnical analysis. Seven 2-D electrical resistivity imaging traverse lines, seven electromagnetic profiles were run and seven soil samples were collected and analysed. Each of the sample point were located on each of the 2-D imaging traverse. Traverses 1-7 host samples 1-7 respectively. The findings revealed high conductivity in unstable areas (resistivity ranging from 11-42 Ohm-m, 1-38 Ohm-m, 4-12 Ohm-m, 1-15 Ohm-m, and 11-30 Ohm-m for traverse 1-5, respectively) and low conductivity in stable ones (resistivity ranging from 19-91 Ohm-m and 109-2056 Ohm-m for traverse 6 and 7, respectively) and they occur at near surface to a relatively shallow depths (ranging from 0-6m depth) in all the profile. Geotechnical analysis showed high clay content in the soil, affecting its engineering properties in most of the studied locations. Soil grain oversize data analysis indicated a range between 70.1% and 75.1% for unstable portions (samples 1-5), with an average of 72.22% fines while percentage coarse ranges between 24.9 and 29.9 with an average of 27.78%. Their optimum moisture content ranged from 10.4% to 11.50%, with a mean value of 11.18%. Also, their plastic index averaged at 10.044%, while linear shrinkage varies between 1.79% and 3.60%, with an average of 2.808%. All these are the responsible factors for the soil instability in this axis of the investigated site. But for the stable portions (samples 6 and 7), Soil grain oversize data analysis is between 18.1% and 18.2% with an average of 18.65% fines while percentage coarse range between 81.9 and 80.8 with an average of 81.35%. The optimum moisture content ranged from 10.4% to 11.50%, with a mean value of 11.18%, the optimum moisture content ranged from 11.3% to 12.0%, with a mean of 11.65%, the plastic index equals zero (0), linear shrinkage varies between 5.57% and 5.71%, with an average of 5.64% and all these parameters are responsible for the stability of these two portions. The California Bearing ratio (CBR) results graded the soil samples into different types with the unstable portion characterised with clay, silty clay and sandy clay while the stable portion are classified into well graded sands. The well graded sands are very suitable for the engineering construction and hence the buildings on this portion showed no cracks and failure because of lack of differential settlements unlike that of the unstable portion characterised with cracks due differential settlements that led to structural failure at those sides of the study site. The geophysical results corroborate well with geotechnical results and these highlight the value of combining geophysical and geotechnical techniques to evaluate the integrity of the subsurface, providing information that is essential for designing infrastructure foundations and determining stability.