Effect of GCL and subgrade type on internal erosion in GCLs under high gradients

GCLs incorporating different combinations and types of carrier geotextile and resting on three different subgrades are examined using a fixed-ring hydraulic conductivity apparatus. The results demonstrate that for GCLs with a conventional woven or nonwoven carrier geotextile and resting on a gravel or geonet, high hydraulic gradients can cause internal erosion within the GCL that can result in an increase in hydraulic conductivity of at least one order of magnitude. The method of GCL construction is shown to be important and GCLs with a scrim-reinforced nonwoven geotextile carrier layer performed better than those with a single light-weight (woven or nonwoven) geotextile carrier. The tests on GCLs with the scrim-reinforced geotextile carrier layer indicated that hydraulic gradients of up to 7000 (equivalent to about 70 m of water head) could be sustained without measurable internal erosion for the cases examined. When the GCLs were resting on a sand subgrade, all GCLs performed adequately (i.e. no evidence of internal erosion) in these tests with applied water heads of up to about 70 m.