Doctor of Philosophy
Civil and Environmental Engineering
Ernest K. Yanful
M. H. El Naggar
Estimating evaporation from unsaturated soil is important for many applications including agriculture, climate, hydrology, water resources, saturated and unsaturated groundwater flow, slope stability, and soil covers. As an example, the long term performance of soil covers, which are widely used in mining and landfill applications to protect the environment, strongly depends on evaporation from their surfaces.
Evaporation depends on both moisture flow within an unsaturated soil mass, which is generally coupled with heat flow, and void ratio and hydraulic and air conductivities, which are in turn affected by stress and strain and resulting soil settlement. This makes thermo-hydro-mechanical (THM) analysis of evaporation necessary. Evaporation also depends on environmental parameters, including air temperature, humidity, net radiation and wind speed. Therefore, considering atmospheric coupling in predicting evaporation is also necessary.
The stress-strain behavior of the soil affects its settlement, which changes void ratio and porosity, and in turn permeability of the soil. This can alter the evaporation characteristics significantly and should be accounted for in any reliable evaluation of the actual evaporation and the performance of soil covers. However, existing soil-atmospheric models such as SOILCOVER(1994) and VADOSE/W(2002), which attempt to represent the soil-atmosphere continuum by linking the subsurface and the atmosphere, do not couple the equilibrium equation. Therefore, they can estimate evaporation but cannot estimate stress, strain and soil settlement. In fact, they perform thermo-hydraulic (TH) analysis.
On the other hand, thermo-hydro-mechanical models such as 2D finite element program θ-Stock (Gatmiri et al., 1999) can perform THM analysis of unsaturated soil by coupling equilibrium equation with moisture and heat flow equations, but only work under soil surface, and do not have the capability to consider the environment and to incorporate atmospheric parameters. Therefore, they cannot estimate evaporation.
The purpose of this study is to bring together the advantages of the above-mentioned programs by using an approach including both ideas and employing a formulation coupling THM analysis with soil-atmosphere modeling. Therefore, the resulting program EVAP1 numerically estimates evaporation from unsaturated soil using THM analysis and at the same time estimates stress, strain and soil settlement. In other words, the program can estimate evaporation considering soil settlement, which occurs in real world.
The program EVAP1 was verified with published experimental and numerical studies on evaporation, including Wilson (1990) and Yang & Yanful (2002). Then, it was used to compare evaporation with and without considering soil settlement. The results showed that soil settlement alters the evaporation characteristics significantly and should be accounted for in any reliable evaluation of the evaporation from unsaturated soil. Neglecting settlement causes an overestimation of evaporation.
A parametric study was also performed to evaluate the effects of environmental parameters on evaporation, in order to identify the parameter that affects evaporation the most. It was found that the most important parameters, in order, are humidity, net radiation, temperature and wind speed. The sensitivity of evaporation to these parameters was also evaluated, and the trend of the change in evaporation due to the change in each of the parameters was noted. The results showed that the effects of these parameters on evaporation are mostly nonlinear.
Mousavi, Seyed Morteza, "Thermo-Hydro-Mechanical analysis of evaporation from unsaturated soils" (2017). Electronic Thesis and Dissertation Repository. 5181.