Design should be interpreted to include both details and conceptual design, as shown by a case study where the consequences of leakage were ignored for a reservoir built on a thin layer of foundation soil overlying a karstic formation, which was overlooked at the design stage. Initial leakage due to a defective connection between the geomembrane and a concrete structure caused soil erosion all the way to an underlying karstic cavity, and eventually the geomembrane burst under water pressure over this cavity. This landmark case study showed that a leakage detection and collection layer without a secondary liner cannot prevent leakage into the ground and provided inspiration for the concept of double liner.

But even if the geomembrane after construction approaches the “zero leak” ideal, holes can be formed during service due to stress concentration at the connection between the geomembrane and a rigid structure, e.g. resulting from differential settlements and/or from inadequate geometry of the rigid structure. Case studies are used to demonstrate that avoiding stress concentrations requires both changing the geometry and understanding the stress-strain properties of the geomembrane. More case studies demonstrate the necessity of a double liner when leakage may cause deterioration of the underlying soil and the perhaps counter-intuitive (i.e. anti-common sense) cautionary note that two liners may not be better than one in the case of reservoirs, where it is possible for liquid to accumulate between them.

The lecture concludes with advice to keep “zero leakage” as an ideal and a reminder of the measures that help engineers get closer to this ideal, and a recommendation to specify an acceptable leakage rate based on (1) an evaluation of the consequences of leakage that is specific to the project being designed and (2) published guidelines, studies and recommendations on acceptable leakage rates.