Leakage of composite cutoff walls through geomembrane joint defects

Composite geomembrane-soil-bentonite (CGSB) cutoff walls are effective barriers to contain highly aggressive contaminated groundwater. Defects in the geomembrane (GM) joint are inevitable during the installation, inducing preferential flow paths. An experimental device is designed to measure the flow rate $Q$ through the joint defects of CGSB walls. Experiments and numerical simulations are performed to investigate the leakage characteristics of CGSB walls. The results show that soil-bentonite (SB) enters the joint under pressure and has a sealing effect similar to a hydrophilic gasket, which effectively reduces the $Q$. As the hydraulic head $h_w$ increases, the internal gap width of the joint increases, resulting in a significant increase in $Q$. When $h_w$ increases from 1 to 2 m, the maximum increase in the measured $Q$ exceeds 17.6 times. The fracture pore diameter $d_f$ of the joint filled with SB decreases by an order of magnitude compared to the case without SB filling. When $d_f$ is less than 0.1 mm, the leakage of the CGSB wall is mainly controlled by $d_f$; while $d_f$ is greater than 0.2 mm, the leakage is mainly affected by the interface transmissivity between the GM and SB.