[6188.8.131.52] The experimental setup of  consists of a vertical cylindrical, long column, whose side walls are impermeable, filled with a homogeneous, isotropic and incompressible porous medium, an unconsolidated sandy material comprising approximately 97.5, 0.8 and 1.7% sand-, silt-, and clay-sized particles respectively. [6184.108.40.206] The two fluids considered here are water and air and water is the wetting fluid. [6220.127.116.11] The top of the column is connected to the atmosphere so that only air can enter the top of the column. [618.104.22.168] The bottom of the column is connected to a water tank and only water can enter from the bottom. [622.214.171.124] The pressure in the tank is adjustable. [6126.96.36.199] Initially, the porous column is completely water saturated and the pressure in the water tank is chosen such that it compensates the water column . [6188.8.131.52] Hence, the capillary fringe is located at the top of the column. [6184.108.40.206] The pressures in this section are given in cm column of water because this translates one to one to the position of the water table in the column. [6220.127.116.11] Below in Section 5 SI units are used. [618.104.22.168] Figure 1 gives a conceptual picture of the experiment.
[622.214.171.124] The column is drained by lowering the pressure in the reservoir by every 13 times until the water pressure reaches . [6126.96.36.199] After a relaxation period of , the water pressure is raised again in seven steps by every and the column is imbibed again. [6188.8.131.52] After , the water pressure is again lowered by every for 5 times and the column is drained again. [6184.108.40.206] Finally, later, the water pressure is raised again by steps every until it reaches its initial value . [6220.127.116.11] However, the original water content in the column is not recovered because a fraction of air remains trapped in the medium .
[618.104.22.168] In the laboratory, water saturation and water pressure have been
measured at height , , and
from the bottom of the column.
[622.214.171.124] It may safely be assumed that the air pressure is
essentially hydrostatic and atmospheric for two reasons: Firstly, because of the high viscosity
and density contrast (,
, ), and
secondly, because the column is short.
[6126.96.36.199] It is therefore concluded that the measurement of water saturation and water pressure suffices to
determine the capillary pressure saturation relationship.