Intergrated Geological and Geotechnical Properties of Subsoil for Shallow Foundation Design at M. I. Wushishi Housing Estate, Minna, Niger State, North-Central Nigeria

Abstract

A study of the geological and geotechnical properties of subsoil for shallow foundation design was carried out at the M. I. Wushishi Housing Estate in Minna, Niger State, North-Central Nigeria. The main aim of the research was to ascertain the lithological and structural characteristics of the study area in order to recommend the suitable shallow foundation design for the proposed building construction. The general geological mapping of the area revealed that the area is underlain by Schist rock belonging to the Kushaka Formation. The principal joint direction in the area is NW - SE. As shown by trial pits, the area are characterized by relatively thick overburden with silty clay in some places which is traceable to the predominant rock type (schist) found in the area. The area is generally low-lying and accessible through Eastern Bye-pass and Maitumbi road. The soil is heterogeneous when correlated laterally from trial pits. Both disturbed and undisturbed soil samples were collected and subjected to laboratory and sieve analysis. The liquid limit ranged from 12.00 - 37.00 with a mean value of 23.85 while the plastic limit varied from 7.27 - 30.73 with an average value of 17.17. The plasticity index varies from 1.79 - 15.13 with a mean value of 6.66 while the shrinkage potential ranged from low to medium. The maximum dry density ranged between 1.66 - 1.95 mg/m3 with the mean value of 1.81 mg/m3 while the optimum moisture content ranged from 8.70 - 21.37 with an average value of 15.16. The natural moisture content is in the order of 11.52 - 29.86 % with a mean value of 21.08 %. The particle size distribution curve showed that the area is sand dominated. Based on the field and laboratory results, shallow foundation (pad/strip) can be adopted for lightly loaded structures not exceeding an allowable bearing capacity of 150KN/m2 while deep/pile foundation are advocated for heavily loaded structures.