STABILITY AND TENSION CONSIDERATIONS REGARDING COVER SOILS ON GEOMEMBRANE LINED SLOPES

The occurrence of cover soil instability in the form of sliding on geomembranes is far too frequent. Additionally, there have been cases of wide width tension failures of the underlying geomembranes when the friction created by the cover soil becomes excessive. While there are procedures available in the literature regarding rational design of those topics, it is felt that a unified step-by-step perspective might be worth while. It is in this light that this paper is written. Included are four separate, but closely interrelated, design models. They are the following: cover soil stability on side slopes when placed above a geomembrane, cover soil reinforcement provided by either geogrids or geotextiles, wide width tension mobilized in the geomembrane caused by the interface friction of the soils placed above and below the geomembrane, and circumferential tension mobilized in the geomembrane by subsidence of the subgrade material beneath the geomembrane. Each of these designs are developed in detail and a numeric problem is framed to illustrate the design procedure. Emphasized throughout the paper is the need for realistic laboratory test values of interface friction, in-plane tension and out-of-plane tension of the geomembranes. By having realistic experimental values of allowable strength they can be compared to the required, or design, strength for calculation of the resulting factor-of-safety against instability of failure.