Swelling Ratio of a Hydrophilic Seal and Flow Rates of the Interlocking System in Composite Geomembrane Cutoff Walls Exposed to Metal-Rich Solutions

The swelling capacity of hydrophilic seals and the sealing performance of interlocking systems in composite geomembrane cutoff walls are crucial for containing the migration of contaminated groundwater. This study examined the swelling ratio at equilibrium of weight (Swe) and of volume (Sve) of commercial hydrophilic seal exposed to metal-rich solutions with varying concentrations and cation valences. A model apparatus was developed to evaluate the leakage behavior of poorly sealed interlocking systems under different hydraulic gradients and solution types. The relationship between flow rate of poorly sealed interlocking systems and swelling capacity of the hydrophilic seal was evaluated. Results showed that the hydrophilic seal reached up to 21 times its own weight in deionized water, and its volume expanded by up to 25 times its original size. At equal molar concentrations, the seal exhibited 25–39 times greater Swe and 24–35 times greater Sve in NaCl solutions than in CaCl2 solutions. Under the permeation of deionized water, 100 mM NaCl, and CaCl2 solutions, the flow rate of poorly sealed interlocking system initially decreased to a minimum and then gradually increased to a stable value over time. The flow rate of the interlocking system decreased with increasing Swe and Sve values of the hydrophilic seal. Furthermore, as the hydraulic gradient increased from 10 to 30, the flow rate correspondingly rose from 0.0028 mL/s/m to 0.7537 mL/s/m.