Challenges of the Filter Paper Suction Measurements in Geosynthetic Clay Liners: Effects of Method, Time, Capillarity, and Hysteresis

Abstract

Time and method dependencies, lack of sufficient capillary connections, and wetting-drying hysteresis may cause inaccurate results from filter paper tests (FPTs) when used for suction measurements of geosynthetic clay liners (GCLs). These limitations of the filter paper method for suction measurements of GCLs were investigated using initially dry contact, initially wet contact, and noncontact FPTs. Wetting-drying hysteresis was observed in the initially dry contact and noncontact FPTs and was significantly higher in the latter. The initially wet contact and initially dry contact FPTs were reliable in measuring matric and total suction, respectively. These two methods can provide suction measurements from both the cover and the carrier geotextile sides of the GCLs (i.e., from the hydratable surfaces of the GCL after installation on site), thus allowing suction measurements without impacting the integrity of the geotextile-bentonite-geotextile structure. Suction measurements on a granular bentonite-based GCL showed higher time dependency compared with powdered bentonite-based GCLs. For the specific GCLs and conditions tested, the woven and nonwoven scrim-reinforced geotextile structure causes pronounced capillary break effects on the hydratable surface of GCL. In contrast, the woven geotextile structure has a minimal impact. When the FPT procedures are applied to GCLs, the interpretation of the results requires careful consideration of the method and time dependencies, wetting-drying hysteresis, capillary breaks, and how the measurements of total or matric suction are performed.