Liquid and gas permeabilities of unsaturated municipal solid waste under compression.

A novel set of experimental apparatus was designed and constructed to study the changes in the fluid-flow properties of municipal solid waste (MSW) related to the physical evolution of its structure under compression. The vertical liquid and gas permeabilities of MSW samples were measured in a laboratory-constructed cell termed an oedopermeameter. Another original device, a gas pycnometer, was employed to assess the volumetric gas content of the porous medium. Finally, the horizontal gas permeability of the compressed MSW sample was measured using another laboratory-constructed cell called a transmissivimeter. The results made it possible to characterise the intrinsic gas permeability as a function of porosity. Additionally, gas permeability measurements of samples with different liquid contents allowed the derivation of gas permeability correlations as functions of the physical parameters of the medium. A unique relationship was found between the gas permeability and the volumetric gas content.

Characterisation of the physico-mechanical parameters of MSW.

Following the basics of soil mechanics, the physico-mechanical behaviour of municipal solid waste (MSW) can be defined through constitutive relationships which are expressed with respect to three physical parameters: the dry density, the porosity and the gravimetric liquid content. In order to take into account the complexity of MSW (grain size distribution and heterogeneity larger than for conventional soils), a special oedometer was designed to carry out laboratory experiments. This apparatus allowed a coupled measurement of physical parameters for MSW settlement under stress. The studied material was a typical sample of fresh MSW from a French landfill. The relevant physical parameters were measured using a gas pycnometer. Moreover, the compressibility of MSW was studied with respect to the initial gravimetric liquid content. Proposed methods to assess the set of three physical parameters allow a relevant understanding of the physico-mechanical behaviour of MSW under compression, specifically, the evolution of the limit liquid content. The present method can be extended to any type of MSW.