The Mercer Lecture is a biennial lecture sponsored by Tensar International with the endorsement of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) and the International Geosynthetics Society (IGS). Brian Mercer (1927-1998) was an English engineer, inventor of geosynthetics products and businessman. The lecture is given in three locations, typically in different continents. Giroud delivered the Mercer Lecture during the Opening Session of the 10th International Waste Management and Landfill Symposium in Sardinia, October 3-7, 2005, in Durban, South Africa, in October 2005, and in Kyoto, Japan, in March 2006. The lecture was also presented in November 2005 in Atlanta, USA, and in April 2006 in Jakarta, Indonesia, and in Shanghai and Hong Kong, China.

Abstract

Geosynthetics are indispensable in modern waste containment and, more generally, in geotechnical and geoenvironmental engineering. They provide new solutions and, at the same time, pose new challenges to geotechnical engineers. The two main geotechnical goals in waste containment design are the control of liquids that transport contaminants and the short- and long-term integrity of landfills. The lecture shows how geosynthetics are used to achieve these geotechnical goals and identifies areas where research and development are needed.

The first part of the lecture addresses the contribution of geosynthetics to liquid control. Composite liners, which associate clay (and/or bentonite geocomposites) with geomembranes, are orders of magnitude more effective than clay alone. However, it is shown that geotechnical engineers are challenged by aspects of material behavior that are unusual in traditional geotechnical engineering, such as desiccation of clay or bentonite even when these materials are covered with a geomembrane, and geomembrane wrinkling due to thermal expansion, two mechanisms that may impair the effectiveness of composite liners. Another aspect of liquid control is the use of drainage layers to collect and remove leachate. The benefits that result from the use of geosynthetic drainage materials are mentioned. At the same time, the challenges associated with these materials are discussed, such as: the equivalency between geosynthetic and granular leachate collection layers, and the design of geosynthetic leakage collection layers to accommodate the flow generated by concentrated leaks. The first part of the lecture ends with a comparison between single and double liners, in particular in the case of landfills in developing countries.