9. Shallow/Near-Surface Structural Applications
Geotechnical Investigation of Settlement Induced by Groundwater Seepage: Case Study From Ile-Ife, Southwestern Nigeria
Adepelumi Adekunle Abraham
Geology Department, Obafemi Awolowo University, Nigeria.
Abstract
A geotechnical site investigation was conducted using the dipole-dipole electrical resistivity and vertical electrical sounding (VES) resistitvity method to ascertain the cause and sources of groundwater seepage observed in the basement of multi-million dollars engineering building located in Ile-Ife, South-western Nigeria, and to investigate the subsurface condition of the soil on which the engineering structure was placed. Five traverses were established around the buildings and dipole-dipole resistivity data and 17 VES were acquired. Four lithologic layers delineated from the resistivity survey include clay, clayey-sand, weathered/fractured basement and the fresh basement. Results obtained shows that the clayey-sand aquifer delineated exhibit distinct heterogeneity in the hydraulic conductivities and permeability which possibly resulted in high flow rate of groundwater beneath the building basement. This might possibly account for the groundwater seepage observed. Also, areas having coefficient of anisotropy of 1.0 and less than 1.5 are delineated as the potential groundwater recharge zones. This anisotropy range indicates high porosity and permeability. A network of bedrock fractures that possibly serve as conduit for groundwater movement was mapped. Some of the pile foundation of the building was placed directly on these fractures which aided the settlement. This study suggests that the buildings have settled uniformly by 26 cm in the last 25 years.
Last modified: Thu Apr 27 20:27:04 2006