We carry out permeability tests, the Lefranc’s one, at a steady or changeable load. These tests have  to be carried out when the perforation or the tests on the premises are in a progress stage, in not rocky grounds under or outside water table.
In the latter case  this is possible after having saturated the ground with water (absorption test). Such a test measure the horizontal permeability of the ground, by making the water flow through a fixed hole.