An experimental approach for determining unsaturated hydraulic properties of rock fractures

An experimental approach for determining the unsaturated hydraulic properties (the relations between capillary pressure, saturation and unsaturated hydraulic conductivity) of rock fractures is developed and tested. Applying this approach to a single fracture, and with only water flowing, the capillary pressure–saturation and unsaturated hydraulic conductivity–capillary pressure relationships of the fracture during drainage and imbibition can be determined simultaneously. To facilitate the test of the validity of the experimental approach and to elucidate the characteristics of water flow in unsaturated fractures, an analogous fracture with parallel, connected channels of different apertures was fabricated. Experiments of unsaturated water flow in the analogous fracture were carried out. Some characteristics of water flow in unsaturated fractures (hysteresis between drainage and imbibition, etc.) were elucidated. Comparison of measured saturation values and theoretical saturation values corresponding to different apertures at the beginning of drainage and imbibition shows that the experimental approach presented in this paper is valid.