A practical solution in delineating thin conducting structures and suppression problem in direct current resistivity sounding

Abstract

In hard rock areas, conventional apparent resistivity measurement using Schlumberger resistivity sound ing fails to detect thin conducting structures (2-D and 3-D fractures filled with groundwater and minera aggregate) concealed at a large depth. In the present study, an attempt is made to way-out the detectio problem of deep seated thin conducting layer. It is proposed to study the apparent conductance simul taneously with resistivity sounding to detect such conductive zones qualitatively. Apparent conductanc is defined as the magnitude of current flowing in the subsurface for a unit applied voltage through cur rent electrodes. Even though such measurement is of qualitative importance, it gives extremely valuabl information for the presence of conductive zones at depth in challenging hard rock terrain. It has bee observed that apparent conductance increases significantly when groundwater bearing fractures and con ductive bodies are encountered in the subsurface. Field data from different locations are presented t demonstrate the efficacy of such measurement. The measurement assists to the conventional resistivit sounding for successful prediction of groundwater zones at large depth in different hard rock areas an is of enormous importance. The approach is also used for possible solution of suppression problem i the DC resistivity sounding when intermediate layer is not reflected in the resistivity sounding curve Finally, the approach can be used together with resistivity sounding to solve many practical problems. © Indian Academy of Sciences.