Thermal Analysis of Cover Systems in Municipal Solid Waste Landfills

Cover temperature variations were determined at four municipal solid waste landfills located in different climatic regions in North America: Michigan, New Mexico, Alaska, and British Columbia. Cover temperatures varied seasonally similarly to air temperatures and demonstrated amplitude decrement and phase lag with depth. Elevated temperatures in the underlying wastes resulted in warmer temperatures and low frost penetration in the covers compared to surrounding subgrade soils. The ranges of measured temperatures decreased and average temperatures generally increased (approximately $2°\mathrm{C}∕\mathrm{m}$ ) with depth. The ranges of measured temperatures $(T_{\max }-T_{\min })$ were $\mathrm{18–30}°\mathrm{C}$ and $\mathrm{13–21}°\mathrm{C}$ and the average temperatures were $\mathrm{13–18}°\mathrm{C}$ and $\mathrm{14–23}°\mathrm{C}$ at 1 and $2\mathrm{m}$ depths, respectively. For soil and geosynthetic barrier materials around $1\mathrm{m}$ depth, the maximum and minimum temperatures were $\mathrm{22–25}°\mathrm{C}$ and $\mathrm{3–4}°\mathrm{C}$ , respectively. Frost depths were determined to be approximately 50% of those for soils at ambient conditions. The main direction of heat flow in the covers was upward (negative gradients). The cover gradients varied between $-18$ and $14°\mathrm{C}∕\mathrm{m}$ , with averages of $-7\mathrm{to}1°\mathrm{C}∕\mathrm{m}$ . The gradients for soil and geosynthetic barrier materials around $1\mathrm{m}$ depth varied between $-11$ and $9°\mathrm{C}∕\mathrm{m}$ with an average of $-2°\mathrm{C}∕\mathrm{m}$ . Cover thawing $n$ -factors ranged between 1.0 and 1.4 and the cover freezing $n$ -factor was 0.6. Design charts and guidelines are provided for cover thermal analyses for variable climatic conditions.