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ABSTRACT
Failure of buildings has been a major concern in Nigeria because of its incessant occurrence, causing damage to life and property. The aim of this project is to assess the structural failures as a result of soil characteristics in Nigeria, which frequently contribute to these failures. Laboratory tests were conducted to determine the index properties and geotechnical properties of the foundation soil based on failure categories. The investigation involved in-situ collection of the disturbed soil samples and were analysed in the laboratory based on British Standard (BS) method for soil testing for civil engineers. Results of the study reveals that the Atterberg limit (Liquid limit ranged from 16.3% to 33.0%, Plastic limits from 11.08% to 19.21%, Plasticity index from 5.22% to 13.79%). The Sieve analysis shows that the percentage passing of the soil samples ranges from 99.2% to 100.0% which indicates clay soil. The Direct shear test revealed that the cohesive strength (c) ranges from 13 kN/m2 to 24 kN/m2 , angle of internal friction (ø°) from 7° to 9.5° and unit weight (Γ) from 27.5 kN/m3 to 29.00 kN/m3 . From the Consolidation test: the total settlement (Pc) ranges from 19.887 mm to 19.929 mm, Coefficient of Consolidation (Cv) of 22.740 m2 /yr and Volume Compressibility (Mv) from 0.0000046 kN/m2 to 0.0000058 kN/m2 . The Specific gravity (SG) from 2.34 to 2.56, and Natural Moisture Content (NMC) from 12.13% to 20.67%. The Compaction test revealed that; the Optimum Moisture Content (OMC) ranged from 11.80% to 17.20%, Maximum Dry Density (MDD) from 1.66 g/cm3 to 1.83 g/cm3 which shows that the soil are mostly of silty-clay material. Furthermore, the soil exhibited shear failures, leading to substantial lateral soil movement. The results of the triaxial test revealed that soils are not fairly within the specifications required for constructions of infrastructure due to their high content of organic matter. The soils exhibited high moisture content, presence of organic clay in the soil and a low preconsolidation pressure is the root cause of subsidence in buildings. Based on these findings, the recommendations for improving soil strength and preventing future failures include methods like preloading, chemical stabilization, adding stabilizers, and constructing retaining walls or embankments. Therefore, there is a pressing need for an extensive research effort to investigate the root causes of structural failure due to soilrelated issues in Nigeria.
