Short- and long-term leakage through composite liners. The 7th Arthur Casagrande Lecture

The factors that may affect short-term leakage through composite liners are examined. It is shown that the leakage through composite liners is only a very small fraction of that expected for either a geomembrane (GM) or clay liner (CL) alone. However, the calculated leakage through holes in a GM in direct contact with a clay liner is typically substantially smaller than that actually observed in the field. It is shown that calculated leakage taking account of typical connected wrinkle lengths observed in the field explains the observed field leakage through composite liners. Provided that care is taken to avoid excessive connected wrinkle lengths, the leakage through composite liners is very small compared to a typical GM or CL alone. It is shown that the leakage through composite liners with a geosynthetic clay liner (GCL) is typically much less than for composite liners with a compacted clay liner (CCL). Finally, factors that will affect long-term leakage through composite liners are discussed. It is concluded that composite liners have performed extremely well in field applications for a couple of decades and that recent research both helps understand why they have worked so well and provides new insight into issues that need to be considered to ensure excellent long-term liner performance of composite liners - especially for applications where the liner temperature can exceed about 35 degrees C.