Measuring Water Retention Curves for Rough Joints with Random Apertures

A water retention curve for joints is a crucial parameter function in the numerical modeling of slopes, liners, and covers containing cracks or joints. In this study, a laboratory apparatus was designed and used to measure the water retention curves for rough joints at very low suctions. The aperture characteristics of the joint change spatially and are described by random-field theory. The apparatus incorporates a uniquely designed end cap and a water-content monitoring and pressure-control system. Suctions can be applied to the joint at an accuracy of 0.005 kPa. Visual observations of the flow process reveal that capillary flow is dominant in a rough epoxy joint with an average aperture size of 0.4 mm. The air-entry value is 0.23 kPa for the joint and decreases with increasing joint aperture size. When the applied suction becomes high, the water phase becomes discontinuous and a residual condition is attained. The residual degree of saturation is 0.26 for the joint with an average aperture size of 0.4 mm and decreases with increasing average aperture size. The rough joint can be viewed as a heterogeneous porous medium. The van Genuchten model can be used to describe the measured water retention curves for the rough joint.