Determination of empirical relations between geoelectrical data and geotechnical parameters at the site of a proposed earth dam

Abstract

In order to establish empirical equations that relate layer resistivity values with geotechnical parameters for engineering site characterization, geotechnical tests comprising Standard Penetration Test (SPT), Atterberg
limit, Triaxial Compression and Oedometer consolidation tests were conducted on soil samples collected from six boreholes drilled to a maximum depth of 20 metres along a proposed dam axis. The locations of the boreholes coincided with VES stations previously occupied along the axis. Atterberg limit test was conducted on the disturbed soil samples while the undisturbed samples were subjected to quick (undrained) triaxial and oedometer consolidation tests. The SPT blows (N) required for the 300 mm penetration following the first 150 mm penetration below the bottom of the borehole was taken as the penetration resistance of the soil.The geoelectrical data and geotechnical parameters were subsequently correlated. The study established that soil electrical resistivity increases with increase in bulk density but decreases with increase in plasticity index, cohesion and coefficient of compressibility. There seems to be no relationship between layer resistivity and Standard Penetration Test (SPT) blow counts, N. Where the correlation coefficients are significant (> 0.90), as for plasticity index, cohesion and coefficient of compressibility, the established empirical equations can be used to estimate geotechnical properties from subsoil resistivity values, thereby reducing the cost and duration of engineering site investigation.

Keywords: Electrical Resistivity, Site Characterization, Dam Axis, Correlation.