Testing system for hydraulic properties of unsaturated nonwoven geotextiles

ABSTRACT: The water retention curve (WRC) of unsaturated nonwoven geotextiles is necessary for the prediction of transient water flow in unsaturated soil–geotextile systems. A test method is introduced in this study to measure the WRC of deformable, unsaturated nonwoven geotextiles. This test method combines the axis-translation technique with water flow control using a flow pump. Specifically, a nonwoven geotextile specimen is placed within a flexible wall permeameter atop a cellulose membrane having high air entry and low impedance, and the flow pump is used to impose upward or downward water flow across the membrane. A control loop is used to reach stable suction values at the boundary of the suction in order to ensure that points on the WRC are defined for equilibrium flow conditions. A piston is used to apply a vertical load on the nonwoven geotextile specimen in order to replicate field loading conditions, and was also useful for measurement of changes in specimen volume. The combination of flow control, suction stabilization, and height measurement allow this new approach to effectively consider the impact of normal stress and matric suction on the porosity of the geotextile during measurement of the WRC. Experimental results for typical tests indicate that this approach yields drying and rewetting WRC curves for a geotextile specimen consistent with those in the technical literature.