A geotechnical investigation on the structural failures of building projects in parts of Awka, southeastern Nigeria

Abstract

Twelve samples of shale from different locations within the Imo Shale Formation in the Awka area (southeastern Nigeria) have been assessed to evaluate the impact of the shale formation on some geotechnical problems experienced by constructed projects in the area. Results indicate that shale samples from the formation have Atterberg limits that might be considered moderate to high; while liquid limit (LL) ranged from 32 - 78, the plasticity index (PI) ranged from 11 - 32. These relatively high LL and PI suggest presence of expansive clays, some swelling of the shale on moisture influx and high compressibility. Natural moisture content (with mean value of 17%) was also significantly high. Despite indicating fair stability as fills (Maximum dry density and soaked California bearing ratio have mean values of 1.85 mg/m3 and 42%, respectively), the formation is likely to have low shear strength, as suggested by its low values of strength parameters (mean value of angle of internal friction is 22°, while mean cohesion is 21 kN/m3). Geotechnical behaviours of the Imo Shale also give indications that the shale failed some relevant material specifications for general engineering purposes and, thus, was significantly responsible for structural failures and foundation problems of buildings that are prevalent in some parts of Awka area.