Quantification of Leakage Through Defects in Inclined Geomembrane‐Geosynthetic Clay Liner Systems Subjected to High Leachate Heads

ABSTRACT Valley‐type landfills in mountainous regions like China utilize sloped composite liners (geomembrane over geosynthetic clay liner, GMB/GCL) to maximize waste capacity. However, high leachate heads and slope‐induced GCL erosion defects significantly increase leakage risks. Although models exist for horizontal liners or isolated GMB defects, no analytical solution quantifies leakage through combined GMB wrinkles and GCL erosion defects on slopes. This study develops a novel analytical model to predict leakage for two critical defect configurations: (1) GCL defect downstream of a GMB defect, and (2) GCL defect upstream of a GMB defect. Solutions are derived from coupled flow equations and validated against finite‐element simulations. Within the studied slope range (0°–45°) and interface contact conditions, key findings demonstrate: negligible net impact of slope angle on total leakage (<0.3% variation); leakage increases of up to 32% (poor contact) and 13% (good contact) due to GCL defects versus defect‐free liners; manageable 3D effects from defect length/orientation (≤22% leakage increase); and critically, no practical impact of GCL defect position (upstream/downstream) on total leakage. These insights enable simplified analysis ( α = 0°) for field‐realistic along‐slope defects and support probabilistic leakage assessments to optimize liner design in slope applications.