title: Effects of dry bulk density and particle size fraction on gas transport parameters in variably saturated landfill cover soil.
abstract: Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, ρ(b), and particle size fraction on the main soil-gas transport parameters - soil-gas diffusivity (D(p)/D(o), ratio of gas diffusion coefficients in soil and free air) and air permeability (k(a)) - under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting ρ(b) values ranging from 1.40 to 2.10 g cm(-3). Results showed that D(p) and k(a) values for the '+gravel' fraction (<35 mm) became larger than for the '-gravel' fraction (<2mm) under variably-saturated conditions for a given soil-air content (ε), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on D(p) and k(a) was most pronounced for the '+gravel' fraction. Normalized ratios were introduced for all soil-gas parameters: (i) for gas diffusivity D(p)/D(f), the ratio of measured D(p) to D(p) in total porosity (f), (ii) for air permeability k(a)/k(a)(,pF4.1), the ratio of measured k(a) to k(a) at 1235 kPa matric potential (=pF 4.1), and (iii) for soil-air content, the ratio of soil-air content (ε) to total porosity (f) (air saturation). Based on the normalized parameters, predictive power-law models for D(p)(ε/f) and k(a)(ε/f) models were developed based on a single parameter (water blockage factor M for D(p) and P for k(a)). The water blockage factors, M and P, were found to be linearly correlated to ρ(b) values, and the effects of dry bulk density on D(p) and k(a) for both '+gravel' and '-gravel' fractions were well accounted for by the new models.
authors.affiliation: Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan. praneeth1977@yahoo.co.uk
authors.forename: Praneeth
authors.initials: P
authors.lastname: Wickramarachchi
authors.forename: Ken
authors.initials: K
authors.lastname: Kawamoto
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Hamamoto
authors.forename: Masanao
authors.initials: M
authors.lastname: Nagamori
authors.forename: Per
authors.initials: P
authors.lastname: Moldrup
authors.forename: Toshiko
authors.initials: T
authors.lastname: Komatsu
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D017752:Greenhouse Effect; D060587:Groundwater / Q000032:analysis; D008962:Models, Theoretical; D010316:Particle Size; D012037:Refuse Disposal / Q000379:methods*; D012987:Soil / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D012987:Soil