Experimental Study On Thermal Conductivity Of Artificial Frozen Clay And Develop Rules Of Multi-freezing-tube Temperature Field

Relevant theorization about artificial freezing method, freezing temperature field,thermal conductivity of frozen soil and its back analysis are expounded firstly in this article, based on it and the Fanwangshi west air shaft freezing engineering which have double circle freezing pipes of different depth, the freezing temperature field are measured and studied, the test and back analysis of thermal conductivity of two representative soil (sandy clay at88m depth and silty clay at155m depth) is performed at the same time, then is the numerical simulation of freezing temperature with the equivalent thermal conductivity tested using ANSYS software, at last, the development of frozen wall are predicted and some advice about freezing are given.Three thermometer holes, located outside the outer tubes, between the outer and the inner tubes and inside the inner tubes respectively, are set in the engineering to measure the temperature within200days mainly in active freezing period, the results shows that all the measured soil temperature have dropped below0℃before80days, then the cooling rate comes down and becomes stable after180days; The measured temperature fields is related to the position of thermometer holes, the average cooling rate of T1, T2and T3are0.21℃/d,0.17℃/d, and0.16℃/d respectively within100days; The freezing method had significant effect on the cooling rate, the average cooling rate of Tl, T2of grit at195m is1.6time as large as that of475m, when the number of freezing pipes is doubled; Several influencing factors, such as moisture content, dry density, soil property and temperature, have been taken into consideration and analysed in the thermal conductivity test, and some significant conclusions are obtained, for example, moisture content and dry density have the most remarkble influence on the thermal conductivity of frozen soil, and the thermal conductivity increasing speed with dry density of freezing silty clay and sandy clay in four moisture contents are about3times and4times faster than that of thawing silty clay and sandy clay respectively; During the process of back analysis, a group of thermal conductivity are arranged with the idea of the selection method and the least square method, the one which has the largest object function value is chose to be the equivalent thermal conductivity, the results are2.0W/(m· K) and1.9W/(m· K) for the two layers respectively. The comparison of freezing temperature between measured values and simulated values shows that the temperature difference of the three thermometer holes are kept within 2℃broadly, which proves the rationality and reliability of the analysis and test in the article.Finally, the freezing temperature field, the thickness and the average temperature of frozen wall at88m depth are simulated and forecasted combined with temperature contour using ANSYS. The advice that we should raise the saline water temperature of inner tubers appropriately to ensure the efficiency and safety in shaft excavation.It is the reliable research method that combines theory, actual measurement, test and simulation together and be used in this article.The research findings which is of high research value and important engineering meaning will cover the shortage of the study on freezing soil thermal conductivity to some extent, while offer one way for back analysis of it and a kind of reference for artificial freezing engineering in homologous geological condition.