10. Lab Experiment to Demonstrate Measurement of Soil Resistivity


Objective To measure the resistivity of a given soil using soil box method.
Materials MC Miller Multi-combination meter


Soil Box


High impedance digital multimeter


Variable D.C. power supply


Copper-copper sulphate reference electrode



The size of the soil box was 1.5 x 2.5 x 9” (standard).  The dimensions are such that when the soil box is filled with electrolyte (water or sand) the resistivity in  ohm cm of the electrolyte is equal to the change in potential between the center or potential pins divided by the change in current.         

The soil box is filled to the rim with the desired soil.  Some water is put in the soil.  Connections are made as shown in figure below.  


The current is switched on by pushing the switch to “on” position. The change in potential is recorded.

The following relationship is used:

              R = (VON - VOFF)/I

where             VON  =  Voltage drop when the power is on.

      VOFF  =  Voltage drop when the power is off.

The resistivity is calculated in ohm-cm2.  Figures below show the typical value of soil resistivity under wet condition in different location.  The Azizyah area is surprisingly highly corrosive.




     The lower the soil resistivity the more is the magnitude of corrosion.