Electrical resistivity tomography and magnetic surveys: applications for building site characterization at Gubre, Wolkite University site, western Ethiopia

Abstract

A study aimed at evaluating the competence of the near surface formations as foundation materials has been undertaken at the site of the newly established Wolkite University Campus. Integrated geophysical surveys involving 2D Electrical Resistivity Tomography (ert), Vertical Electrical Sounding (ves) and magnetic surveys have been used for the purpose. The ert and ves results show the presence of intermediate to low resistivity top soil, an even lower resistivity second layer of clay and/or high moisture content underlain by weathered and fresh bedrocks, and a number of vertical or near vertical discontinuities and weak zones in the site.  The magnetic anomaly plots, have mapped the weak zones resulting from subsurface structures and the Euler depth map and 2d magnetic modelling specially depicting the depth of the magnetic sources that are associated with the bedrock. The correlation of the magnetic anomaly plot and 2d inverse model resistivity sections are used for the identification of weak zones that need special building design consideration at the site. The work emphasizes the viability of high resolution electrical tomographic surveys in engineering site investigations to augment geotechnical investigations that depend on data from a limited number of points to characterize large areas and complex geologic settings.