Modelling nonisothermal gas conductivity function of unsaturated rooted soils

In the landfills, the degradation of municipal solid wastes (MSWs) generates greenhouse gases and releases heat (i.e., self-heating). Although vegetation has been commonly found in the landfill cover system, there is no model to predict nonisothermal gas conductivity function (GCF), and how the elevation of temperature would affect gas transport of unsaturated rooted soils remains unknown. This study aims to propose a new model to predict the nonisothermal GCFs of unsaturated rooted soils considering temperature effects on soil thermodynamic properties and soil water retention curves. The newly proposed model was validated against the measured GCFs of unsaturated rooted sandy soil under different temperatures and degrees of saturation (S_r) by a tailor-designed experimental apparatus. Test results showed that the gas conductivity (K_g) increased by about one order of magnitude with the reductions in S_r. There existed a threshold S_r (approximately 0.65), above which the gas phase became discontinuous, causing a significant drop in K_g. Moreover, K_g reduced with increasing temperature, mainly because of increased gas dynamic viscosity; but the preferential path of gas transport induced by root shrinkage due to temperature elevation might counteract these effects to a certain extent. Unlike existing models requiring experimental data at different temperatures, the newly proposed model needs only one set of data measured at ambient temperature. The proposed GCF model could satisfactorily capture the temperature effects on unsaturated rooted soils (with average R² and average RMSE of 0.903 and 1.88×10⁻⁷ m/s, respectively), especially for temperature range less than 323.15 K (50 °C) before potential root death.