Geoelectrical and Geotechnical Evaluation of Subsoil at a Proposed Engineering Site, NE of Baghdad City

Abstract

Subsoil evaluation within a proposes site for civil engineering structure by using geoelectrical and geotechnical methods of investigation carry out. The study aims to provide information on the stratigraphy, thickness, nature, and competence of the subsoil. Eighteen (18) Vertical Electrical Sounding (VES) stations using Schlumberger configuration occupy and complement with geotechnical analysis of eighteen (18) soil samples collect at all the VES points at depth not exceeding 1m within the study area. The VES interpretations delineate four main geoelectric sequences which comprise of the top soil, mixture of clay and sand, gravely sand and sandy gravel. The top soils are generally thin (< 2 m) and majorly composes of clayey silt/ silty clay /sandy clay/ clayey sand/ fill materials. The layer resistivity ranges from 0.75-19.6 Ωm for topsoil, 1.71 - 6.7 Ωm for clay and sand mixture, 0.01 – 2.69 Ωm for saturated gravelly sand layer and 4.23- 4.61 Ωm for saturated sandy gravel layer. Low resistivity values at the study area are due to moisture and clay content within deposits at the study area. The geotechnical results show that the soil is relatively high clay content, intermediate to high moisture content and high plasticity. It concludes from the combined results above, that the topsoil is generally geotechnically less competence soil and may not serve as a good foundation material, therefore shallow foundation may not be feasible in studied area and, for engineering structure to be erected on such soil there is need for soil improvement or pilling to the sand layer.