Assessment of frost and heating penetration in compacted clay layers of landfill top covers in temperate climate

Abstract

Compacted clay (CC) layers are commonly used as hydraulic barriers in landfills, thanks to their impervious capacity. However, mechanical and hydraulic properties of CC can be significantly affected by temperature variations due to the heat produced by waste degradation as well as to external air temperature and weathering. Previous experimental tests show that the most detrimental occurrence is the cyclic freezing–thawing (FT) that can increase the hydraulic conductivity of CC up to one order of magnitude. This paper aims at assessing the temperature distribution in a landfill multilayered top cover in several scenarios of temperature solicitations, in order to evaluate the depth of frost penetration. For this purpose, a 2D hydro-thermal coupled finite element model representing a case study landfill top cover has been developed; each constituting layer has been characterized by physical and thermal properties acquired through direct measurements on sampled materials in unfrozen and frozen conditions. The model provides a reliable time description of the isotherm distribution within the layered top cover in several temperature scenarios typical of a temperate climate, thus estimating the penetration of the frost front as well as of high temperatures.