Geotechnical Site Investigation of Two Failed Buildings in Enugu Metropolis, South East Nigeria

Résumé

Abstract Foundation integrity investigation was carried out on a building in Enugu State University of Science and Technology permanent site in Nkanu west and Godfrey Okoye University, Thinkers' Corner, Enugu East Local Government Area. Both locations are in the Enugu state,Nigeria. In recent times, lives and properties have been lost to building failures in the study area hence; this study seeks to reveal the reason for the cracks seen and possibly deduces the cause(s) of building failures in the area studied. At the foundation level in the different corners of buildings, samples were collected and geotechnical tests were conducted. The results showed that the area is made up of 50–70% clay fraction soil and has intermediate to high plasticity. The Liquid Limit and Plastic Limit range from 46–58% and 23–32% respectively while the Plasticity Index ranges from 21–28%. The area also showed an increase in moisture content as it ranged from 19.54 to 34.99%. The MDD and OMC which range from 1.65–1.74(g/m3) and 16.6–18.2% respectively show that the soil samples studied are not fit for foundation purposes. The Triaxial test showed high cohesion values of 29.06–37.62 KN/m2 and a low angle of internal friction of 4.74–8.880. Due to high cohesion, the area has improved bearing capacity from 241.77 to 305.2 KN/m2. The average coefficient of consolidation is 0.1392 m2/yr. in "E Section" and 0.1902 m2/yr. in "G Section". The coefficient of volume change (Mv) ranges from 4.10 x10− 5 m2/KN to 4.1x10− 4 m2/KN in the "E Section" and from 4.1 x10− 5m2/KN to 3.4 x10− 4m2/KN in "G Section. The porosity value ranging from 25.90–36.15% in the E section and from 29.80–35.20% in the G section shows the soil in the study area can take in water as much as possible which then finds it difficult to leave because of low permeability ranging from 9.99 x 10− 13cm/sec to 2.12 x 10− 5cm/sec and causes water log at the site. X-ray diffraction (XRD) results showed the presence of the kandite group of minerals occurring with goethite, magnetite, quartz, hematite, muscovite, and feldspar. The Soil in the studied area undergoes compression as seen in values of Coefficient of consolidation showing that soils in both locations are highly compressible meaning the building is underlain by an incompetent soil layer experiencing differential settlement in an amount ranging from 2.06 x10− 4m2/yr. to 3.44x10− 3m2/yr. in "E Section" and from 3.11 x10− 4m2/yr. to 2.90 x10− 3m2/yr. in the "G Section which can be minimized by proper surface and underground drainage systems.

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