EXPERIMENTAL INVESTIGATION ON EVAPORATION PROCESS OF WATER IN SOIL DURING DRYING

Evaporation of water saturated in soil is a time-dependent process of decreasing water content.It is always accompanied by the evolution of soil fabric,stress-strain state as well as soil engineering properties.It is also an initiator of many geotechnical engineering problems.In this investigation,desiccation tests under different temperatures(25~45℃)were carried on initially saturated clayey soil with various layer thicknesses(5~11mm).The water loss of the specimen during drying was monitored and the corresponding evaporation curve was obtained.The results show that the evaporation process of soil water occurs in three fairly distinct stages: constant rate stage,falling rate stage and residual stage.After analyzing the evaporation characteristics and the intrinsic mechanism involved in each stage,it is found that the constant rate stage generally occurs at the initial drying period,where the water content is relative high and the specimen is still saturate.During the constant rate stage,the profile moisture transfer is dominated by liquid flow and mainly controlled by capillary force,and the evaporation rate significantly depends on environmental factors or limited by the amount of energy available to vaporize soil moisture in the upper layer of the soil.The decrease of vapor pressure gradient on the evaporation surface,transfer velocity of profile moisture,profile suction gradient,availability of water amount and the increase of pore air are the primary factors that result in the evaporation transition from constant rate stage to falling rate stage.During the falling rate stage,the profile moisture moves in both liquid and vapor forms and the later one gradually dominates the evaporation process,the evaporation rate is mainly limited by the soil conditions and pore structure.In addition,it is also found that higher temperature corresponds to higher initial evaporation rate and shorter drying period,while the initial evaporation rate is less sensitive to specimen thickness changes; thicker specimen needs longer drying period.