Effects of soil characteristics on moisture evaporation

Evaporation of water from soils is a three-stage process that has great significance in stress development in exposed geotechnical structures, generation of dusts that can cause environmental pollution and respiratory ailments, and dereliction of land by generating drought conditions. In this study, the factors that influence water evaporation from soil have been divided into two categories: external, referring to atmospheric conditions and interior, covering surficial soil characteristics and water content conditions. Particularly, five different sets of laboratory based evaporation tests were performed using cylindrical (150 mm diameter and 7-28 mm height) samples of clayey soil mixed with quartzite sands (three grainsize ranges: 0.2-0.5mm, 0.5-1.0mm, and 2.0-3.0 mm) in weight proportions ranging from 0% to 50% to evaluate the effects of soil texture, mineralogy and initial compactive state on its free water evaporation process at room temperature (20-22 degrees C) and relative humidity (50 +/- 2%) conditions. The evaporation tests were performed using mass loss measurements on soil samples to an accuracy of 0.01 g. Findings show that in the first stage of soil drying, water content decreases continuously with time while the ratio of actual to potential evaporation, E-a/E-p stays mostly stable. During the falling rate stage, both water content and EaEp decrease significantly. However, the water content varies but not significantly due to the low value of residual evaporation rate in the residual evaporation stage. Soil with lower sand content starts the falling rate stage at higher water content: 32.52% at added sand proportions of 0% versus 21.87%, 20.65%, 20.45%, 20.26% and 18.34% at added sand proportions of 10%, 20%, 30%, 40%, and 50% respectively. Larger soil sample thicknesses accelerate water evaporation rate and extend the constant evaporation rate stage. Soil particle size was not found to have significant impact on evaporation rate on per unit weight of added soil basis. The evaporation rate increases in direct proportionality to increase in initial water content and dry density.