Experimental Study on Pot Lid Effect of Canal Soil Under Unidirectional Freezing
Water evaporation during soil freezing is hindered by the composite geomembrane laid in rigid-flexible composite lining canals in cold and arid regions,and the phenomenon of soil water increase under the composite geomembrane,that is,the"pot lid effect".In order to explore the mechanism and rule of the pot lid effect of soil,soil columns with different moisture content were prepared and unidirectional freezing test was carried out.The influence of composite geomembrane on soil column temperature and water field was analyzed.The results show that the cooling rate of soil column covered with composite geomembrane and the temperature difference between soil layers are lower than that of soil column without composite geomembrane.During the freezing process,the water at the bottom of the soil column without the composite geomembrane is transferred to the top continuously through the pore channel of the soil,and then evaporates,and the water content of the whole soil column decreases,and the distribution is uneven.For soil columns covered by composite geomembrane,the moisture content of the soil at the bottom decreases under the action of water migration and pot cover effect,while the moisture content of the top soil under the membrane increases significantly,and the pot cover effect under the membrane is frozen,which indicates that the soil under the composite geomembrane has an obvious pot cover effect during the freezing process.Soil columns with different initial moisture content have different amounts and forms of water transfer under the influence of pot lid effect.The increase of water transfer in the top layer of soil column with small initial moisture content is mainly caused by gaseous water transfer,while the increase in water transfer in soil column with large initial moisture content is mainly caused by liquid water transfer.
rigid-flexible composite lining canalpot lid effectunidirectional freezingtemperature fieldmoisture migration
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