BEM Solution for Design of Trenches in Multilayered Landfills

Abstract

A two-dimensional (2D) numerical model for a convection-diffusion flow of a mixture of gases through a multilayered porous medium has been developed with the aim to obtain criteria for the optimal design of venting trenches for gas collection from a landfill. The proposed numerical scheme is based on the boundary element formulation of the governing equations, in which the dual reciprocity method (DRM) is used to transform the resulting domain integrals to the boundary. The scheme is improved by the use of a domain decomposition algorithm, which allows a better representation of the physical problem. From present numerical analysis it can be concluded that it is sufficient to construct venting trenches that only cross the top covering layer of the landfill, as long as there are provided enough pathways to guarantee a gentle gas flow across the separation layers between waste layers inside the landfill. Venting structures that cross the entire depth of the repository, as it is usually done in landfill design, are not necessary.