GEOTECHNICAL INVESTIGATION OF BUILDING FAILURE: CASE STUDIES OF SEMS BUILDING, FUTA AND FOURSQUARE GOSPEL CHURCH, ISINKAN-AKURE, SOUTHWESTERN NIGERIA.

Abstract

The colossal loses incurred as a result of failed structures is usually enormous. This necessitates investigating causes of failure whenever it occurs. The buildings of School of Earth and Mineral Sciences (SEMS) and Foursquare Gospel Church, Isinkan, both in Akure, have shown significant failures and were therefore chosen for investigation. Fifty-four soil samples were collected from the two locations. Investigative tests conducted on the soils include: Natural moisture contents (NMC), specific gravity, atterberg limit, sieve analysis, compaction, triaxial and Cone Penetrating Test (CPT) tests based on various standards such as: Federal Ministry of Works and Housing (FMWH) (1997), Unified Soil Classification System (USCS) and American Association of State Highway and Transportation Officials (AASHTO) standard, etc. The results indicated an increase in the NMC at SEMS and Isinkan from top to the base layers. The top layer revealed an average of 16.25%, middle layer 20.41% and the base layer 22.26% at SEMS location while at Isinkan, the top was 24.29%, middle layer 28.9% and base layer 30.71%. These values were relatively high, indicating that the soil potential for water retention is high. The results of the grain size analysis at SEMS showed that percentage fines ranges from 39.8% to 61.8% with an average of 43.36%, 55.65% and 58.4% for top, middle and base layers respectively indicating a high percentage of clay/silt content and consequently of high compressibility. At Isinkan, the percentage fines ranged from 7.1% to 9.3% with an average of 9.76%, 8.06% and 8.06% for top, middle, and base layers respectively, implying that they have high percentage of coarse materials. The samples at SEMS location were clay of high compressibility, therefore, cannot be recommended for sub-grade subbase, and base materials, while all the samples at Isinkan location can be deduced as suitable for sub-grade sub-base, and base materials. The compaction characteristic of the soil samples at SEMS revealed that the MDD values decrease from top to base layer while the OMC increase downward. The MDD for top layer was 1759.75Kg/m3 , the middle layer was 1719.25 and base layer 1570.63 Kg/m3 , while the OMC for top layer was 17.29%, for middle layer was 18.44% and for the base layer was 21.75%. The MDD values for Isinkan increase from top to base layer while the OMC decreases downward. The MDD for top layer was 1864.14Kg/m3 , the middle layer was 1823.29Kg/m3 and base layer 1907.50Kg/m3 while the OMC for top layer was 14.83% for middle layer 15.56% and for the base layer is 13.62%. In view of the above, samples in this location can be recommended for base course, sub-base, sub-grade, and earth fill materials. The results revealed that there are correlations between the MDD/OMC and the %fines from the study areas. The results of the triaxial test showed high cohesive bond and shear strength parameters with the angle of internal friction (φ) ranged from 25.1o to 40.7o while the cohesion (c) ranged from 30.3 (kPa) to 162.9 (kPa). It also revealed that the cohesion increased downward with 71.86 (kPa) for top layer, 85.37 (kPa) middle layer and 105.45 for the base layer. The analysis of the results showed that the average allowable bearing capacity for the top, middle and base layers at SEMS are 66.02kN/m2, 154.55 kN/m2, and 257.07 kN/m2, respectively while that of Isinkan, revealed an average of 38.57 kN/m2, 120.58 kN/m2, and 251.1kN/m2 respectively. This implies that the allowable bearing capacity was reasonably high from middle to base layers at the two sites, suggesting that samples at these locations would have considerable strength and likely to withstand shear stress. In view of many factors highlighted above and other engineering parameters that made the soils unfavorable for engineering purposes might have contributed to what could have caused the structural failure of buildings in the two locations and consequently noticeable cracks on their walls and floors in the case of the building at SEMS location