Experimental Research And Numerical Simulation On Moisture Migration Of Unsaturated Loess Under Unidirectional Freeze

There is obvioussuccession of the seasons in distribution areas ofloessand largetemperature difference between day and night.And the temperature change will producesignificant moisture migration movement.This moisture migration may affectdirectlythe normal use of the building, lead to slope failure in freeze areas,uplift or cracking ofthe foundation soil, impact seriouslyon agricultural growth and environmentalprotection about seasonal frozen and so on.Soin view of the seriousness of the issue, ifunsaturated loess moisture migration law was mastered of, the law will play a very goodrole in guiding the production activities of the human. Therefore, to carry out the studyof loess moisture field mobility movement has a very important significance.Research the impact on temperature andmoisture migrationof soil in different drydensity, initial water content, cold junction temperature and freezing rate by usingdeveloped test and monitoring equipment.The testing results show thatmoisturemigration is from the warm side to the cold side; the water content increases mostsignificantly at freezing front; and soil dry density, initial moisture content, freezingtemperatures and freezing rate may effect the temperature ormoisture migrationof soil.With the steady growth in dry density, cooling sample process becomes slow down; andthe freezing front of the water content value increases as the frontal position coordinatesdecreases. As the initial moisture content increases, the cooling process developsheavily as well as improvement of the water content significantly at the freezing front.The cold junction temperature affects the position of the freezing front, temperature ofthe cold end is the lower, the final value of freezing front position coordinate is thegreater. Changing freezing rates will impact on the value of the water content at thefreezing front in different time, and would leaad to several extreme points in the watercontent graph. In order to considering the influencing factors of unsaturated loess moisturemigration comprehensively, Harlan equation is amended accordingly. By usingunsaturated soil permeability tester, permeability coefficient of the relationship curveswith water content and dry density are obtained, the permeability coefficient of theregression formula is deduced by further analysis of the test data. In order toquantitative calculation for different dry density, initial water content and the coldjunction temperature of moisture migration, heat and mass migration parameters aredetermined by combining with other factors of empirical formula. Each numericalcalculation result of sample shows that the Harlan equation can better reflect impact ofsoil parameters and external conditions on moisture migration.Comparing numericalcalculation results indicates that calculation accuracy of the low water content of soilsamples is higher than the high water content of the soil samples.