Today’s post; the Schlumberger array is part 2 of a series of short posts on Soil Resistivity Testing methods. Part 3 The Wenner 4 Probve & Part 1. The Driven Rod Method. And also, the common mistakes encountered. Along with, practical advice on how to avoid Soil Resistivity Testing 10 Common Mistakes.
Soil resistivity testing carried out using different methods, below is another of the three popular approaches to perform soil resistivity testing:
By the way, this soil resistivity testing method is more economical than the Wenner 4 Probe Test when it comes to the human resources required to perform the task. The outer electrode can be moved four or five times for each move of the inner electrode .
Figure 2 shows the arrangement for the Schlumberger Array.
When contact resistance, which is the resistance of the top layer of the ground, is very high, this can lead to an error in the reading of the machine during soil resistivity testing.
Every machine has maximum loop impedance, in some cases where the soil resistivity of the top layer is very high, that will lead to a loop impedance more considerable than the maximum loop impedance of the machine.
In this case, apply the Schlumberger array to the reciprocity theorem. This soil resistivity test method, known as the Inverse Schlumberger Array (ISA). Also, using this method it provides a safer working environment for the resistivity tester under high current supply. And, it reduces the more massive cable needed during the soil resistivity test.
Soil Resistivity Calculation
Calculate the soil’s resistivity using equation 2:
L is the distance the centre from the outer probe
l distance to the centre from the inner probe