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This paper assesses the causes and socioeconomic impact of some recent cases of collapsed buildings in Nigeria. Information on selected collapsed buildings was collated, and a case study of a failed one-story building is presented for emphasis. A summary of the technical assessment and remediation of the building was presented as well. Both field and laboratory work involved close inspection of the building, excavation to reveal the condition of the foundation, taking samples of slabs and beams from the collapsed building for laboratory study, detailed structural analysis, a design analysis of the structural elements of the building to reveal causes of failure, and identification of remedial options and recommendation. Solubility of concrete in acids was used to assess the quality of concrete used. This study revealed that a lot of lives and properties have been lost in the various collapsed buildings, and these losses have negatively impacted the socioeconomic status of Nigerians. The results of the case study revealed that the main structural components (slab, beam, column, and footing) of the building were not properly proportioned and were seriously underreinforced, which led to excessive deflection. Additionally, concrete mixes used in the construction were found to be weak, and walls that should have been non-load-bearing ended up carrying loads and induced a hogging moment onto the slab for which reinforcement was not provided. The solubility tests showed that the ratio of calcium concentration of concrete mix used in the collapsed building to that of standard 1:2:4 concrete mixes were 0.03, 0.20, and 0.73, respectively. These low ratios indicate that the cement portion in the concrete was not adequate, and it was concluded that the concrete samples from the collapsed building contained less calcium than necessary for structural success. The summary of the assessment underscored the need for ensuring quality control and proper supervision in the construction of reinforced concrete structures.

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This paper investigated the effect of cement kiln dust (CKD) and periwinkle shell ash (PSA) on the plasticity characteristics of two lateritic soil. Two Soils (termed soil A and B) were collected from two selected locations within Osun State, Nigeria. Air-dried soil was treated with CKD and PSA blend in order of 0, 5, 10, 15, and 20% for CKD and 0, 2, 4, 6, 8 and 10% for PSA by dry weight of soil. The specific gravity of both soils increased with increase in CKD and PSA fillings. The Index properties such as Atterberg’s limit (liquid limit, LL, plastic limit, PL, and plasticity index, PI), percentage fines content of the soils was determined. The index properties results showed that the two soils are clayey soil of low plasticity. There was a general decrease in the Atterberg’s limits (liquid limit, LL and plastic limit, PL). The scan electron microscopy (SEM) and electron diffraction spectroscopy of treated soil revealed the formation of crystalline products of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) which was responsible for strength gain. Based on preliminary investigations, the study concluded that the combination of CKD-PSA blends is a viable stabiliser for the two tropical soils under consideration to be used as sub-base construction.

The source of groundwater seepage problem being experienced by some engineering buildings in a part of southwestern Nigeria was investigated by carrying out comparative study of the hydraulic conductivity (K) of the soil types underlying the area using integrated approaches involving geotechnical and geophysical methods.Soil samples were collected from six different towns on which standard geotechnical tests including natural moisture content, grain size distribution, linear shrinkage, specific gravity, liquid and plastic limits, compaction, triaxial and K test were carried out. Also, geophysical data were acquired at seventy-two locations using Schlumberger array with a current electrode spacing of 40m. The resistivity data obtained were subsequently inverted to obtain the subsurface 2D hydraulic conductivity section.The results obtained imply that the soil types investigated is semi-pervious with K values ranging from 1.06 x 10-5 to 5.71 x10-5cm/s. These values suggest moderate groundwater flow which might account for the seepage that was observed. Four lithologies (lateritic topsoil, clayey-sand, sandy-clay and fractured/weathered bedrock) were delineated. The geotechnical analysis result suggests the soil investigated could be classified as poorly graded sandy-clay and/or silty-clay. This soil exhibit plasticity index ranging from 12.72 to 19.75%, with specific gravity ranging from 2.47 to 2.73; the maximum dry density (MDD) varies from 1699.5 kg/cm3 to 1915kg/cm3 and the optimum moisture content (OMC) ranges from 12.05% to 16.32%.The result of the t-test results performed implied that at 95% t–confidence level, there is a good correlation between the results obtained from both approaches employed.