A dual-porosity model for coupled rainwater and landfill gas transport through capillary barrier covers

Abstract

A two-dimensional dual-porosity model for coupled rainwater and landfill gas transport through capillary barrier covers (CBCs) was established. The proposed model was partially verified using published data from a laboratory loess column test. By fitting the field-measured data using the proposed model, the optimal dual-porosity parameters of the in-situ loess of a loess/gravel CBC in Northwest China were determined to be wf = 0.1 (volume fraction of macropore system), Kf/Km = 150 (intrinsic permeability ratio of macropore to micropore system) and Re = 1 (reduction factor of mass exchange at the interface between macropore and micropore systems). This model was used to predict the performance of the CBC experiencing a 15-day rainfall period followed by a 30-day no-rainfall period. Results showed that the presence of macropores induced an earlier occurrence of percolation accompanied with a higher percolation rate. The cumulative percolation and CH4 emission rate derived from the dual-porosity model were about 50 % and one order of magnitude higher than those predicted by the single-porosity model, respectively. In addition, the existence of gravel layer had remarkable influence on minimizing water percolation and CH4 emission, but these were practically independent of its thickness. The results of this study can provide an effective method, crucial parameters and guidelines for the design of CBCs.