Geotechnical Response of Compost Biocover Columns under Freeze-Thaw Conditions

Abstract

Biocovers are a promising technology for mitigating methane (CH4) emission from landfills. The geotechnical performance of the biocover material is one of the design criteria of biocovers. However, current understanding of the geotechnical behavior of biocovers under freeze-thaw conditions is limited. In the present paper, the effects of freeze-thaw cycles (FTCs) on the geotechnical (thermal, hydraulic, and mechanical) properties of compost-based biocovers are investigated by column experiments. In the experiments, three columns are developed, prepared, and treated by a period of methane injection (0 FTCs) after 1 FTC and 2 FTCs in three respective stages. In addition, extensive laboratory testing is carried out on the biocover samples with regard to their thermal (thermal conductivity); hydraulic (hydraulic conductivity); and mechanical (compressibility and shear strength) and physical properties (e.g., grain size distribution, moisture content). The results show that the FTCs induced changes in a number of the geotechnical properties of the biocover. However, these changes are mostly located in the top layer of the biocover (0–15 cm). It was found that FTCs significantly increased the hydraulic conductivity of the top layer of the biocover, whereas they slightly decreased the thermal conductivity of this layer. As for mechanical and physical factors, the average grain size of the compost surface slightly decreased throughout the stages, while the friction angles of the bottom and middle layers of the compost-based biocover were not significantly affected. The results presented in this paper will contribute to better design of landfill biocovers in cold regions.