To determine the amount of water that a soil can transport at a given pressure gradient, the hydraulic conductivity kf is determined. The value depends on the type of soil (pore size distribution) and the water saturation in the soil. The greatest hydraulic conductivity is achieved when the soil is completely saturated with water. The usual kf measurements in soil science are carried out with comparatively high gradients, which rarely apply to the natural water movement in the soil. HARTGE therefore advocated measurements with very small gradients.

The hood permeameter by HARTGE meets this requirement. It is a laboratory device for the manual determination of the kf value on water-saturated cylinder samples in the laboratory from the flow rate and the associated pressure difference with the smallest possible pressure gradients. Laboratory measurements allow the kf value to be determined under defined boundary conditions, which allows a high repetition rate of the tests and thus also a sound statistical evaluation of the parameters determined.

Test procedure

The saturated sample in the soil sample ring is placed in a tray on a sieve plate and completely submerged in water. A hood filled with water is placed over the soil sample ring, under which a pressure gradient is created along the sample height. This hood is suitable for the soil sample rings offered by UGT so that the soil sample ring can be inserted directly. In the test run, the volume of water flowing through the sample in a specific measuring time is determined at a stationary flow rate. The flow area and length of the flow path are determined by the geometry of the soil sample ring. Depending on the version, the pressure gradient is displayed as a height difference on the standpipes or recorded by a pressure sensor.