| The construction of underground rail transit is an important means to solve the problem of urban development.subway cross passage constructs process in Tianjin,there is a lack of technical specification of freezing method,the design and construction many draw lessons from Shanghai area,in the freezing time and the freezing effect have phenomenons like long duration,excessive freezing and excavation difficult.In this context,the geological condition of Tianjin area is badly needed to refine the corresponding parameters,to optimize the design and guide the construction purpose.In this paper,based on the construction of Tianjin subway Line 5 and 6,selects the representative soil condition for multi working condition of large box freezing test,by changing the arrangement of the freezing pipe,the temperature distribution on the three characteristic interfaces of the frozen wall is obtained,and the variation of the thickness and average temperature of the frozen wall when the different staggered way of freezing pipe is also analyzed.Considering the influence of groundwater flow on the freezing effect,In this paper,the freezing experiment table of fine sand under the condition of the cold source and seepage is established,The temperature value of 0cm,5cm and 20cm three kinds of water level conditions were monitored,then contrast and analyse that the influence of seepage on the development characteristics of freezing temperature field.The numerical model was set up for the freezing test of the large model box,and the distribution of the freezing temperature field under different seepage velocity was simulated by ANSYS software.The results show that:1)For the three characteristic surface,the temperature change rate is the lowest in the interface:frozen for 4.75 days,the lowest temperature of axis surface is-2.5?,the freezing front has been developed to 18cm,the main face of the corresponding values were-0.7 C and 16cm,and the interface of the minimum temperature is only 1.5 C,not frozen.When the pipe staggered arrangement,when the tube spacing is certain,the final hole distance increases 10cm,the closure time of the final hole on the line is extended for 8 days,the average temperature of staggered area decreases slowly,finally stable temperature from-8.5 to-4.5?;The more deviation from the end position of the axial line,the more obvious the superposition effect of the temperature field.2)When the seepage direction is perpendicular to the cold transfer path,with the increase of flow intensity,the different temperature distribution of upper and lower reaches exacerbates,and the amount of cold accumulation is obvious.When the cold source temperature is constant,The stable time of temperature field decreases with the increase of seepage strength.Under the condition of-15?,the freezing front development speed(5,20cm)decreased 65.91%,77.27%compared with 0cm water level,the soil average temperature increase of 1.87?and 2.76?.When-25?,the above corresponding values are50%,66.67%and 0.81?and 1.90?.3)horizontal seepage source,when V<8.64m/d,the regression function between the time of frozen wall intersection and flow velocity is y=0.09557x~2-1.54221x+9.37958. |
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