Permeant Properties of Foundation Soils in the Basement Complex Terrain of Southwestern Nigeria

Abstract

Previous investigations on foundation soils of the Basement Complex Terrain of Southwestern Nigeria revealed a wide range variation in coefficient of permeability (K) due to grain sizes. Compared to findings on geotechnical properties of foundation soils in general, permeant properties due to grain-size distribution in relation to the rate of settlement, has not been discussed. This study focuses on the concept of permeant properties to clarify the relationship between K and grain-size distribution for the purpose of rate of foundation settlement. Grain-size distribution of the soils was carried out by sieve analysis method and hydrometer test for coarse and fine soils respectively following the British Standard. The effective size (D₁₀) and a constant of 0.015 were employed in the estimation of K, based on Hazen formula. Inverse relationship exist between K and amount of clay (r = -0.34), K and amount of silt (r = -0.29) as well as exists between K and amount of sand (r = -0.015). It follows that the amount of clay in the soils decreases with K, and rate at which water flows in the soil will rather influence the rate and amount of foundation settlement. However, fairly strong positive correlation (r = 0,58) exists between K and amount of gravel with line of best fit K = 0.006 %Gravel + 0.047. This study has shown that the permeability of the foundation soils increases with amount of gravel.