Study On Migration Law Of Unfrozen Water In Artificial Freezing Process Under Vertical Freezing Front

The distribution of soil moisture after artificial freezing is caused by the migration of unfrozen water during freezing.The current research focuses on simulating the migration of unfrozen water under natural freezing conditions,and there is less research on the migration of unfrozen water under artificial freezing.The natural vertical freezing front is often pushed forward in horizontal direction,which is different from natural freeze-thaw from top to bottom.In this paper,in view of the characteristics of the migration of unfrozen water in artificial frozen soil,the temperature control plate is arranged in the horizontal direction by model test,and the soil is frozen in the horizontal direction.Two types of freezing methods,one way water replenishment and two ends closed,were selected to simulate the migration of unfrozen water when the single ring and multi circle freezing pipes were arranged.The real-time variation of unfrozen water content during freezing is obtained by using NMR equipment and moisture sensor.The results are as follows:(1)The basic physical parameters of Xuzhou silty clay,including density,particle size distribution,saturated moisture content and plastic and liquid limit,are analyzed.The freezing characteristic test was carried out by NMR and EC-5 water sensor.The initial freezing temperature and the freezing characteristic curve of Xuzhou silty clay were obtained.The freezing characteristic curve of unsaturated soil based on the freezing characteristic curve of saturated soil was put forward.The initial water content from the plastic limit to the saturation range and the Xuzhou powder viscosity were obtained.The formula of soil empirical coefficient and its freezing characteristic curve.(2)The freezing test system was designed by myselves to simulate the migration of unfrozen water in the freezing soil of single loop freezing pipe,and the unfrozen water migration test under the condition of unidirectional water supplement was carried out.By freezing the right water supplement on the left side of the soil,the real-time changes of the unfrozen water and temperature during the freezing process were obtained.The concept of unfrozen water migration period,in situ freezing period and stable period during the freezing process was defined,and the unfrozen water migration amount,in situ freezing amount and stability amount at the corresponding stage were obtained.(3)The migration law of unfrozen water in the process of freezing soil freezing in multi loop freezing pipe was simulated by the unfrozen water transfer test under the closed condition of the two ends.The migration of unfrozen water was increased obviously,the migration of unfrozen water was promoted,and the effect of reducing the area of the unfrozen water decreased and the freezing temperature was improved.It will directly delay the speed of the frozen front propulsion,thus increase the migration time of unfrozen water,increase the migration of unfrozen water and increase the redistribution of soil moisture after freezing,and increase the initial water content of the soil will lead to the decline of the freezing front propulsion rate,the delay of the freezing front intersection time,and the increase of the migration time of the unfrozen water.The migration of high unfrozen water can also provide sufficient water for unfrozen water migration and also promote the migration of unfrozen water.