Study of the Effects of Poor Drainage Design on Building Foundations in Ibadan, Oyo State

Poor drainage design in the urban environment of Ibadan, South West Nigeria, contributes to waterlogging and foundation undermining that accelerates building deterioration and structural failure. This study investigated the relationship between drainage deficiencies and foundation distress in 60 residential and commercial buildings in Ibadan North, Ibadan South West, and Ido Local Government Areas. Physical inspection documented drainage conditions (surface drainage adequacy, groundwater table depth, and proximity to drainage channels) and foundation distress indicators (differential settlement, wall cracking, and floor heave). Soil samples were collected from four foundation trench sites near distressed buildings for moisture content, plasticity, and bearing capacity analysis. Building professionals (n = 25) were interviewed on observed drainage-foundation relationships. Results showed that 78% of buildings with recorded foundation distress were located within 20 metres of a blocked or inadequate surface drain. Foundation bearing capacity ranged from 34 to 78 kN/m2 in waterlogged locations, significantly below the design requirement of 100 to 150 kN/m2 for most residential construction. Clay soil expansion under cyclic wetting and drying was identified as a primary mechanism of foundation movement in 41% of distressed buildings. The study concludes that drainage design and foundation design are poorly coordinated in Ibadan residential construction, and recommends that drainage master planning be integrated with building site design guidelines in the Ibadan Urban Master Plan.

Keywords: drainage design, building foundations, foundation distress, Ibadan, waterlogging