Landfill capping stability: tapered solution with seepage

The capping system is one of the major structural elements in modern landfills. When using artificial sealing materials (e.g. a geomembrane) as the capping liner, the stability of the cover soils and integrity of the geosynthethics need to be assessed. Traditional design methods only consider uniform cover soil thickness with different degrees of saturation and seepage build-up (i.e. parallel submergency ratio). This paper proposes an analytical method which includes the seepage build-up in the stability analysis for the capping slope with a tapered cover soil profile, that is when cover soils become thicker from top to bottom. Both the parallel (modified) and horizontal seepage force build-up patterns have been considered and analysed. The proposed analytical methods are applied to a design case in which uniform thickness cover soils are considered. The results are comparable to those of the traditional methods and therefore they are verified. Parametric analyses have confirmed the tapered profile can effectively improve the capping slope stability and indicated that the interface shear strength (between the cover soil and the underlying geosynthetic) and cover soil shear strength have the most significant effects on the capping slope stability.