Study On The Calculation Methods Of Average Temperature And Thickness Of Multi Row Pipe Artificial Freezing Wall

With the new development of urbanization in China, the construction of underground rail traffic has become a practical method to solve the "traffic difficulties". Freezing engineering is often needed in underground engineering activities due to groundwater. Assessing the effect of freezing engineering accurately is the key to the quality of the project. The thickness of the frozen wall and the average temperature are important indexes to assess the effect of freezing engineering, however, the empirical formulas which have been applied in the engineering nowadays still can not accurately calculate the multi- hole situation. On the basis of actual measurement of the vertical portal Nanjing Subway Project, the paper gained accurate temperature field data after e ffecting numerical analysis on actual projects with the help of finite element software. It obtained temperature distribution curve through the temperature field data, then it applies the curve fitting equation, deriving analytic formulas of freeze wall thickness and the average temperature algebraically. In the end, the paper compares the analytical formulas with methods of computation summed up by our predecessors, and it studies their applicability from the aspects of convenience and accuracy. The paper draws the following main conclusions:(1) The measured data indicates that the the temperature dropped slowly when the freezing comes to 10 to 15 days, and it gets into the transformation stage. The temperature dropped more slowly in 20 days. The fact has been fully proved in numerical simulation that the freezing pipes will cross nearly completed in 10 to 15 days and a complete freeze wall will form in about 20 days.(2) The paper extracts data from numerical simulation of temperature field, drawing the conclusion that regularity of temperature distribution from outermost freezing pipe to frozen wall edge region is class linear distribution. It also derives the analytic formulas of freeze wall thickness.(3) The paper extracts data from numerical simulation of temperature field, deriving temperature distribution curves on section of center and ground wall vertical of freezing pipes on Section I and Section III. Then it draws the analytic formulas of average temperature of no underground continuous wall of frozen wall through algebra calculation. In the actual project, when there is a ground wall on one side, the temperature will b e 0.8℃ higher than when there are no ground walls. It derives the analytic formulas of average temperature of no underground continuous wall of frozen wall after the correction factor is added.(4) The paper extracts data from numerical simulation of temperature field, deriving temperature distribution curves on section of center and ground wall vertical of freezing pipes on Section I and Section III. Then it draws the analytic formulas of average temperature of no underground continuous wall of frozen wall through algebra calculation. In the actual project, when there is a ground wall on one side, the temperature will b e 0.8℃ higher than when there are no ground walls. It derives the analytic formulas of average temperature of no underground continuous wall of frozen wall after the correction factor is added.(5) The analytical formulas of the thickness of the frozen wall, which are drawed by this paper, are simple and intuitive as well as convenient. The analytical formulas are more accurate than existing emprical formulas because they are drawed according to temperature distribution. However, in order to applying the analytical formulas accurately, the outside thermometer hole of freezing pipe has to be located on the cross- section I, also known as the cross- section of center and ground wall vertical of freezing pipes.(6)Average temperature of frozen wall analytic formula for polynomial operation s, operational, practical. Through the fitting curve formula of intermediate point data w ith the original datacomparing the simulation accuracy is relatively high, meet the req uirement of Engineering application. In order to simplify the calculation work, the inte rsection point temperature measuring hole middle section and cross section of II in the two row tube, so the temperatureis measured.(7) The analytical formulas are drawed on the basis of portal analog multi-row vertical pipe freezing temperature field, and they can also be applied in the calculation of multi-row tube wall thickness and average temperature of service channel and the subway entrance.