Foundation Soil Characterisation for a Building with Multiple Cracks at Tarkwa, Ghana

Formation of cracks on buildings could be attributed to many factors such as properties of soils, geology, structural defects and climatic conditions. A public building at Tarkwa in the Western Region of Ghana developed cracks that rendered it unsafe and so it was demolished for a new structure to be put in place. Geotechnical investigations were undertaken to ascertain possible contributions of the foundation soils to development of these cracks before it was demolished. Site investigations on test holes and laboratory analyses showed that, the foundation soils were mainly dense silty sand, with average moisture content of 8.9% and specific gravity of 2.7 Kg/m³. These characteristics are typical of quartz sands. Though the soil at the site where the building was situated was non-plastic, plasticity index (PI) for soils at neighbouring sites ranged from 1.5% to 7.8% at an average of 4.9% and so consolidation immediately after structural loading was negligible and might not result in differential settling. Moisture content was lower than liquid limit as liquidity indices were between -0.326 to -12.653. These soils exhibited minimal liquefaction potential and were free draining. They were of high permeability and therefore could consolidate immediately after being subjected to structural load. Hence the foundation soils played little role in the formation of cracks on the building which was exposed to frequent ground vibration as the building was close to a defunct underground mine, heavy vehicular traffic and a railway station; with surface mining activities at a permitted distance.