ELECTRICAL RESISTIVITY METHODS

Resistivity method is considered to be active geo-physical method. This method employs an artificial source which is introduced into the ground through a pair of electrodes. The procedure involves the measure the potential difference between two other electrodes in the field of current flow such that apparent resistance is calculated. Resistivity method generally consists of two pair of electrodes. Each pair of electrodes is called current and potential electrodes. The electrode by which current is introduced in ground is called current electrode. And electrode between which measure the potential  difference (p.d) are called potential electrodes.

In this figure, let us consider A and B be a pair of current electrode and C and D be a pair of potential electrode.  And the total potential at the potential electrode C is due to the contribution of two current electrodes A and B respectively. That means the total potential at C is sum of potential contribution of current electrode A and B.

Solving this we can get to the value we need . i.e. Here apparent resistivity is calculated by knowing the value of “p”. Up to this we knew how to calculate apparent resistivity. So now, we need to know about the procedure for resistivity survey. Mainly there are two main type of procedure used in resistivity survey. They are: 1)         Vertical Electrical Sounding (VES) : a)         It is also called electrical drilling. b)        The current and potential electrodes are maintained at the same relative distance.   2)         Constant Separation Traversing (CST) :   a)         It is also called electrical profiling and used to determine lateral variation of resistivity. b)        Current and potential electrodes are maintained at fixed distance.   So these two procedures are used respectively in resistivity surveying. This surveying process is used in geological investigation like construction, hydrological investigation , mineral exploration e.t.c.