Thermally induced water movement in uniform clayey soil
Benjamin, J. G.
Drying of a soil surface can lead to cracking, thereby creating large channels for waste to leach out of a landfill site. Temperature affects the rate of drying. Water movement induced by thermal gradients was studied with physical experiments using soil columns and with numerical experiments using a computer program. Clay soil material was moistened to 0.407 or 0.392 m 3 /m 3 water content. The moistened soil was packed and compacted to a density of 1.45 Mg/m 3 into 0.3-m long columns. The soil columns were closed at the top end using black plastic discs and closed at the bottom end using plexiglas discs. The soil columns moistened at 0.407 m 3 /m 3 were subjected to natural radiation for 55 days and those moistened at 0.392 m 3 /m 3 were subjected to elevated radiation levels provided by heat lamps for 54 days. Both levels of radiation create periodic temperature boundaries at the ends of soil columns. The numerical model describes coupled heat and water transfer in the soils. The soil columns receiving elevated radiation had more net water movement from the hot ends toward the cold ends of the soil columns than did the soil columns exposed to natural radiation. The model predicted the soil water content distributions well along the soil column compared with the measured water content. The study shows that there may be some drying of compacted soil under a plastic landfill liner as a result of temperatures and thermal gradients created when the liner is exposed to the high periodic temperature regime in comparison with the low periodic temperature regime. The drying was limited to the surface 20 mm. The computer program was also used to simulate the condition of constant boundary temperatures. Temperatures of 50 and 20°C were used at the hot and cold ends, respectively. The numerical study with constant thermal gradients showed that, compared with periodic temperature regimes, large amounts of water migrated. The drying was extended to a depth of 70 mm. Decomposing buried waste that generates heat can lead to a constant thermal gradient in the clay liner. This can cause more severe drying and cracking than a liner surface exposed to the natural periodic heating and cooling of the environment. Generated heat may accelerate deterioration of the plastic liner as well.
This article is published as Nassar, I. N., J. G. Benjamin, and R. Horton. "Thermally induced water movement in uniform clayey soil." Soil science 161, no. 8 (1996): 471-479. Posted with permission.