Effect of Open and Closed System Freeze-Thaw Cycles on Geosynthetic Clay Liner (GCL)-Geomembrane Interface Transmissivity

Abstract

Testing was conducted to establish the interface transmissivity between a high-density polyethylene (HDPE) geomembrane and a geosynthetic clay liner (GCL). Specimens were subjected to 5 open system freeze thaw cycles (i.e., GCL with water available during freezing) and 25, 50 and 100 closed system freeze thaw cycles (i.e., GCL with no water available during freezing). The freeze-thaw cycling was applied at low stress (2 kPa) and after, the interface transmissivity test was conducted, at applied stresses of 10, 25, 50, 70, 100 and 150 kPa. Closed system GCL samples were pre-hydrated with deionized water (RO) and simulated pore fluid (GS). Open system GCL samples pre-hydrated from the subgrade below prior and during the application of freeze-thaw cycles. The study found that closed system freeze-thaw cycles had little effect on interface transmissivity and, its effect at low stress levels (10-25 kPa) was beneficial (i.e., it decreased interface transmissivity). The study also confirmed Jabin et al. (2022)’s findings, that ice lenses form at the GMB-GCL interface. Open system freeze-thaw cycles increased the interface transmissivity at low stress (≤ 25 kPa) but the effect was eliminated at 50 kPa and above. To explore the effect of scale on interface transmissivity after being subjected to freeze-thaw cycles, new apparatus was developed to allow larger open system freeze-thaw cycles and the interface transmissivity test to be conducted avoiding disturbance of the GMB and GCL specimen. The apparatus has an insulated 0.60 m diameter cell, with a holed GMB in direct contact with a GCL over a subgrade (either silica sand or Godfrey silty sand). The GCL specimen was allowed to pre-hydrate from the subgrade under 10 kPa stress. The freeze-thaw cycles applied in a temperature-controlled room by decreasing the room temperature to -24oC and thereby inducing a one-dimensional freezing front advancing from the geomembrane down through the GCL and into the subgrade. The temperature at the bottom of the cell was maintained at 12°C using a heating mat. Once the necessary freeze-thaw cycles were applied, transmissivity test was then conducted with this new apparatus. The thesis provides the first results from this new apparatus.