人工冻结粉土未冻水含量测试试验研究

TEST STUDY OF UNFROZEN WATER CONTENT IN ARTIFICIAL FROZEN SILT

未冻水含量测试是冻土科学研究中的一个重点和难点问题。为测定粉土中未冻水含量,将小体积土样冻透后,放置在温度恒定的空气中,依靠自然对流加热融化,记录其中心温度–时间变化曲线。根据牛顿冷却定律,建立一个反映冻土温度随时间变化的计算模型,应用该模型拟合温度–时间曲线的融土部分,得到融土与空气表面的对流传热系数;拟合温度–时间曲线的相变部分,确定某地区的粉土冻结点。根据冰的质量和相变过程吸收热量的关系,建立冻透状态下未冻水含量的计算模型及测试方法。应用该方法进行粉土未冻水含量测试,结果表明,该粉土冻结至-4℃时未冻水含量在3.75%左右。反演土样融化过程的理论计算温度与实测值吻合较好,表明了提出的理论模型及测试方法的可行性。

How to determine the unfrozen water content in frozen soil is still a key and difficult problem in geocryology.For measuring the unfrozen water content in frozen silt in laboratory,silt samples are taken into isothermal air to melt by natural convection after being frozen at a negative temperature with the temperature-time history recorded.Based on Newton s law of convection exchange,a analytical model reflecting the variation of the temperature with time throughout whole process is formulated.Some important parameters such as the convective heat transfer coefficient,freezing point and length of melting time are then obtained by fitting the temperature-time history of the tests.On the relationship between ice mass and quantity of heat absorbed in process of thawing,a thermal model of the unfrozen water content in practically frozen state is presented.The results indicate that the unfrozen water content in silt in practically frozen state is about 3.75% when temperature is-4 ℃.Based on the unfrozen water content obtained by this method,the process of the sample melting is then back analyzed.It shows that the analytical results match well with the measured temperature,and feasibility of the proposed analytical model and test method is proved.