Cross Hole Resistivity Tomography Survey for Geological Mapping

Abstract

Geophysical Surface Techniques have been widely used at various stages of a site investigation program ( Clayeton et.al., 1995 ) for engineering structures (New construction or Restoration), as indirect means to define the subsurface conditions, the location, depth and the lateral extent of adverse strata areas representing cavities and weak zones within the underground strata up to the desired depth of the investigation; and whether they pose a risk to the proposed development or to an existing building. In urban areas, site constraints, access and ambient noise strongly influences the validity of employing surface geophysical techniques to investigate subsurface conditions at construction sites. The employment of borehole geophysical technique represents an alternative solution. Electrical Resistivity Tomography is a well known geophysical technique routinely used in site investigations. Cross Hole Resistivity Tomography in which both current and potential electrodes are places in boreholes, can provide detailed 3D information about resistivity distribution of underground strata. In this study, Cross Hole Electrical Resistivity Tomography technique was employed for a multistory building construction site to define the subsurface conditions and to locate adverse high risk strata within the underground up to 40m depth with an aim to increase the resolution in mapping of geological structures and hazards.