Effects of Specimen Size in Transmissivity Tests of Biplanar Geonets and Geocomposites

Hydraulic transmissivity, or the volumetric flow rate per unit width of specimen per unit gradient, is the most important design parameter for a candidate geonet or geocomposite to be used for in-plane drainage applications, such as landfill leachate collection systems or landfill cover drainage systems. The 305 mm wide by 305 mm long box of the American Society of Testing and Material D4716 in-line transmissivity test method has been extensively used to determine the transmissivity of a candidate geosynthetic product over the past one and half decades. However, our study showed that significant effects of the specimen size and the flow direction can be generated on some biplanar geonet or geocomposite samples in D4716 transmissivity tests. The theoretical derivations and actual test results are presented and discussed.