Effect of temperature on gas breakthrough and permeability of compacted loess in landfill cover

In China, municipal solid waste containing large amounts of kitchen waste possesses the characteristics of lower cellulose content (15% on a dry basis) and a faster CH₄ generation rate. This promotes the emission of hazardous gases and the increase in gas pressure in landfill cover systems. The higher temperature further aggravates the aforesaid phenomena. The present work investigated the temperature effect on the gas breakthrough pressure (GBP) and permeability of compacted loess. The water permeability k_w increases with increasing temperature. The intrinsic water permeability K_W independent of pore fluid properties behaves just in an opposite manner. K_W would have been increased with increasing temperature if the rigid wall of the permeameter had not been intervened in the permeability tests. The intrinsic permeability K_G also decreases with the increase in temperature. Although the higher K_G neglects the gas slippage effect, the combination of the thermal expansion of minerals, the transformation of bound water to free water, and the thermal expansion of free water causes pore water to migrate into macropores. Such a pore water migration is accompanied by the water-gas boundary moving to the vadose zone. On the other hand, the capillary pressure shows a correspondence with the GBP value. The higher temperature reduces the difficulty for gas molecules to overcome the surface tension at the water-gas boundary, corresponding to the lower GBP value. The findings provide critical guideposts concerning the design of the gas breakthrough and permeability of compacted loess in landfill covers under the temperature effect.