Multiscale transmissivity study of drain-tube planar geocomposites: effect of experimental device on test representativeness

ABSTRACT: Hydraulic transmissivity is the most important design parameter of geocomposites used for in-plane drainage applications. This paper presents an in-depth investigation of the hydraulic behaviour of drain-tube planar geocomposites (DTPGs) and characterises the locations and causes of head losses based on a multiscale experimental approach using three different apparatus. In particular, a transmissivity rig that accommodates specimens up to 1 m² was developed to define the minimum representative surface area required to characterise DTPGs. The experimental data acquired in this study support a theoretical relationship linking head losses that occur within DPTGs to flow rate. This relationship is used to analyse the results obtained with other transmissivity rigs and to identify the key locations where head losses develop. In addition, evidence that Colebrook's equation can be applied to corrugated tubes is presented. Based on this study, it is concluded that the measured DTPG transmissivity is significantly affected by specimen length and by the experimental device used to make the measurement. For example, the DTPG transmissivity measured in accordance with ASTM D4716-08 was found to be 14% lower than the actual DTPG transmissivity.