| The seasonal frozen soil area in northern China is short of water resources,with cold and dry weather where the evaporation rate is relatively high in winter and spring.Under the effect of seasonal freeze-thaw action,the transformation between shallow phreatic water and soil water are intensely,and the evaporation process of phreatic water is more complex,which is easy to cause adverse geological environment problems such as soil salinization.Therefore,exploring the effects of freeze-thaw and soil physical properties on shallow phreatic water evaporation has certain theoretical significance for scientific and reasonable evaluation of groundwater resources and prevention of soil salinization.Three kinds of shallow phreatic water evaporation freeze-thaw tests with the phreatic water depth of 1.0 m under man-controlled freezing temperature were conducted by indoor freeze-thaw test device in this research.The effects of soil particle size,soil grain size distribution and sand-layered on soil temperature and phreatic water evaporation were analyzed.The regression relationship between cumulative phreatic water evaporation and freezing time and soil particle size distribution was discussed.The results are as follows:（1）Soil particle size had a significant effects on soil temperature and phreatic water evaporation.Under the action of constant temperature freezing at-25℃,the soil temperature decreased rapidly and the evaporation of pheratic water tended to be stable easily.The larger the soil particle size was,the faster the soil temperature changeed,but the phreatic evaporation was smaller.The soil temperature of 0-30 cm soil column with particle size of2.0-2.5 mm was 1.61～2.75℃lower than that of 0.1-0.5 mm soil column,and the cumulative phreatic evaporation was 30.66 mm lower than that of 0.1-0.5 mm soil column.In the process of thawing,the larger the soil particle size,the faster the soil temperature rise.The average daily rising range of soil temperature of 0-30 cm soil column with particle size of 2.0-2.5 mm was 2.17～3.30℃,which was 0.19～0.32℃higher than that of 0.1-0.5 mm soil column.（2）The effect of soil grain size distribution on freeze-thawing soil temperature and phreatic water evaporation was significant.The soil temperature of 0-30 cm in the soil column with the best soil grain size distribution（Coefficient of uniformity Cu=19.08,Curvature coefficient Cc=2.80）decreased the most,ranging from 15.90℃～25.53℃when the slow constant temperature freezing stability(the 62nd day of freezing);in the process of thawing,the soil temperature increased rapidly,with an average daily rising range of 1.65～2.61℃.The soil temperature of 0-30 cm of the soil column with the worst soil grain size distribution（Coefficient of uniformity Cu=3.47,Curvature coefficient Cc=1.35）decreased only by 14.21～23.79℃when the slowly constant temperature freezing stability;in the process of thawing,the soil temperature increased slowly,with an average daily rising range of 1.46～2.37℃.When the slowly constant temperature freezing stability the cumulative phreatic water evaporation of the soil column with the best soil grain size distribution was 54.17 mm,34.14mm higher than that of the column with worst soil grain size distribution.The results showed that cumulative phreatic water evaporation and freezing time were fitted by linear regression between 0-26 days,and fitted by power function regression between 27-62 days.The regression coefficient increased with the increased of the soil grain size distribution,which indicated that the better the particle grain size distribution was,the faster the phreatic water evaporation rate was.（3）Under the action of constant temperature freezing at-25℃,the closer the sand-layered was to the surface,the more obvious the inhibition of soil temperature and phreatic water evaporation was.The soil temperature of 0-50 cm with sand-layered soil columns with placement depth of 10 cm,20 cm,30 cm and 40 cm below surface were0.90～2.19℃、0.80～1.88℃、0.60～1.20℃and 0.31～0.58℃higher than that of homogeneous soil column,respectively.Compared with pheratic water evaporation of the homogeneous soil column,cumulative phreatic water evaporation of sand-layered soil columns with placement depth of 10 cm,20 cm,30 cm and 40 cm below surface were decreased by 53.7%、39.8%、30.8%and 15.9%,respectively.In the process of thawing,the average daily rising range of soil temperature were 0.10～0.24、0.09～0.20、0.06～0.11 and 0.04～0.06℃lower than that of homogeneous soil column,respectively. |
