Hysteretic Moisture Characteristics and Hydraulic Conductivities for Glass‐Bead Media

Abstract

The hysteretic effects in the moisture characteristics and the hydraulic conductivity characteristics of two different glass‐bead media were measured while unsteady water flow was occurring. A gamma‐ray moisture sensor, a combination of pressure transducers and tensiometers, and a capillary‐tube flux meter were combined with a simple box‐like flow chamber for simultaneous measurement of (i) the degree of saturation, (ii) the water‐phase pressure, and (iii) the hydraulic conductivity. These quantities were recorded through out water‐pressure changes which traversed the main‐branch wetting and drying curves as well as the families of “rewet” and “redry” scanning loops. Large hysteresis was recorded in the relation of pressure to saturation or to conductivity. The relation of conductivity to saturation showed hysteresis which, though significantly larger than the experimental error, would for most practical purposes be negligible. The independent domain theory of hysteresis was used to check the relation between the “rewet” and “redry” families of moisture characteristics. By this test the theory was found to be very poorly suited to a description of these media. Two basic approximations of the theory were assumed to be responsible for this lack of applicability.