Environmental Impact Assessment of Structural Defects Using Geophysical and Geotechnical Methods in Parts of Ekpoma, Southsouthern Nigeria

Abstract

This study has evaluated the immediate and remotes causes of structural/foundation failures arising as a result of geodynamic activities that often bring about weathering/fracturing process. Three geophysical techniques were deployed and complemented with geotechnical analysis. The geophysical techniques include 2-D imaging using Dipole-Dipole, Lateral Horizontal Profiling technique which give useful information on the nature and trends of the sub-surface and structural trends and Vertical Electrical Sounding technique using Schlumberger electrode configuration which gave relevant information on layer sequences/stratification as well as variations in lithology/lithological distributions. The geotechnical analysis gave relevant information on the nature, types, grain size analysis and other soil parameters that has direct impact on foundation integrity. The results obtained from the Dipole-dipole and Wenner techniques indicated six weak zones of major interest while the Vertical Electrical Sounding delineated three major layers which are topsoil, clayey sand/ sandy and moderately resistive sandstone formation. The geotechnical analysis indicated the results obtained from both field and laboratory tests which shown that the specific gravity ranged from 2.64 to 2.65; linear shrinkage ranged from 5.0 to 7.1;the amount of fines (i.e. particles less than 0.075mm sieve) from the particle size analysis test ranged from 34.4% to 36.7%; liquid limit varied from 29.4% to 32.2%; Plasticity index varied from 10.2 to 11.9; from the compaction test optimum moisture content and maximum dry density varied from 13.6% to 14.2% and 19.38kN/m3 to 19.49kN/m3 respectively; unconfined compressive strength range from 181kPa to 227kPa. The results obtained from both methods gave relevant information on factors that were responsible for cracks/subsidence and failure of the building.