Preconstruction Investigation of Soil Plasticity Index and Unconfined Compressive Strength of a Hypothetical Building Site

The soil Plasticity Index (PI) serves as one of the key determinants for building stability, especially in areas with clay that are susceptible to swelling and shrinkage. Foundation of buildings is affected, where the soil moisture is beyond acceptable limits or where the soil strength is compromised by water. The study was designed to investigate the soil PI and the Unconfined Compressive Strength (UCS), towards enhancing foundation planning and design. The soil samples obtained for the geotechnical tests were taken at three different depths (0.5, 1.0 and 1.5m), in 36 locations. Microsoft Excel and JASP statistical software was employed for the descriptive and the inferential statistics conducted to analyse the data obtained. Furthermore, Geographic Information Systems (GIS) and Global Positioning Systems (GPS) was utilised for the spatial model using ArcGIS 10 8. The soil was classified as slightly silty gravel-sand and the mean of the moisture contents were 19.01 ± 3.89, 20.19 ± 3.29 and 21.27 ± 2.74 for 0.5, 1.0 and 1.5 m respectively. The liquid limits, plastic limits and the PI of the soil from the three depths ranges from 24 to 61%, 8 to 63% and 0 to 33% respectively. Apart from the 0.5 m layer, the spatial model shows inverse spatial relationship from 1.0 to 1.5 m layer, denoting that places with high PI are of low UCS and vice versa. The regression analysis was non-significant at 0.5, 1.0 and 1.5 m and this was largely attributed to the variations in the soil properties because of the combination of silt, gravel and sand occurring together at the three depths. Soil PI and UCS were investigated and the spatial model obtained serves as proper guides in foundation studies. Itis important to focus empirical models between PI and UCS on specific sites, as generic applications may lead to poor performance, which may lead to building failures and eventual loss of lives and properties.