The permeability test is one of the "in situ" tests carried out to carry out a geotechnical reconnaissance. There are different forms of testing that can be grouped into three: permeability tests in pits, in boreholes and in wells.

In any case, the average permeability of the area affected by the test is obtained, which varies between a few decimeters to hundreds of meters. There is always uncertainty about the ratio of anisotropy to soil permeability and, in soils made up of several materials, about the relationships between the permeabilities of each one. With certain test arrangements, it is possible to obtain data that allows the estimation of these ratios, but in general it is an unknown factor in the interpretation of the test.

In pits, it is possible to carry out permeability tests by filling with water to a level higher than the surrounding water table, and then measuring the decrease in the water level in the test over time, or by draining the water inside and subsequently allowing the level to recover.

In any case, the test allows, by applying the corresponding formulation, to estimate the permeability coefficient by measuring the recovery time.

The same test variants are possible in survey (Lefranc tests). For the test, the tubing is raised somewhat, leaving a drilling portion at the bottom without lateral tubing. The test is then carried out, in any of its modalities (fixed or variable load, water supply or drainage).

In the case of constant load tests, the water level in the borehole is maintained by adding a certain flow rate. The flow rate that is filtered depends on the permeability, the shape:.

where H is the difference in water levels between the interior of the borehole and the water table, and k is the soil permeability coefficient. The proportionality factor, n, depends on the control conditions of each case (diameter of the borehole, length of the area without casing, proximity of impermeable strata, etc.).

for.

for.

In the case of variable load tests, the amount of water level drops in a given time is measured. The corresponding expression is: