Anti-seepage performance of polymer-enhanced three-layer cover system of landfill: Field monitoring and numerical modelling

Landfill cover system plays a crucial role in reducing leachate generation by limiting rainwater infiltration. This paper evaluates the field performance of a polymer-enhanced three-layer cover system at a leather sludge dump site in Xinji city, China over a 1-year monitoring period. Waste soil (WS), sand-bentonite mixture (SB), and sand-polymer-bentonite mixture (SPB) were used as the low-permeability layer, respectively, in three test areas, above which the fine-grained cultivated soil and gravel were used in the top and middle layers to form a capillary barrier. During the 1-year monitoring period, the recorded cumulative rainfall was 452.1 mm, and the volumetric water content (VWC) at the top layer fluctuated significantly from 0.13 to 0.45 in response to rainfall and evaporation, but that of the low-permeability layer maintained stable for both cover SB and SPB. No water percolation was detected during the 1-year monitoring period. Furthermore, numerical simulations were carried out to assess the anti-seepage performance under more extreme climatic conditions (i.e., higher rainfall intensity and long-term deterioration of soil permeability). Numerical simulations corroborated the field observations that the SPB layer effectively minimized percolation even under extreme climatic conditions. For example, under the most unfavourable conditions, the computed annual percolation through the cover SPB was 4.7 mm, as low as 27.2% and 8.1% that through the cover SB (=17.3 mm) and WS (=57.9 mm). Overall, the results suggest that the polymer-enhanced three-layer soil cover is a promising alternative to traditional geomembrane-based covers and/or thick composite soil covers.