Formation process of freezing wall of subway cross passage in seepage stratum and analysis of its influencing factors
Artificial ground freezing is one of the common methods for the construction of subway cross passage due to good water sealing,wide adaptability and less environmental impact.However,delayed time of closure time,thickness and average temperature of the frozen wall are easily caused by groundwater seepage,which has a negative impact on the progress of freezing engineering.Based on the theory of heat transfer and seepage flow in porous media,a hydro-thermal coupling model in saturated strata considering phase change was proposed.The functional relationship between the unfrozen water volume fraction of saturated sandy gravel and temperature was established using frequency domain reflection method.The proposed model was verified using the results of model test.On this basis,the effect of seepage velocity,refrigerant temperature,freezing tube diameter and seepage temperature on the formation process and closure time of the freezing wall was investigated.Finally,the significance analysis of the influencing factors on the formation process of freezing wall was conducted using orthogonal experimental methods,and a prediction method for closure time and standard time of freezing wall considering multiple factors was proposed.The results show that the freezing temperature field of the cross passage is symmetrically distributed in a W-shape without seepage flow.At 51.2 m/d,ground temperature field is asymmetrically distributed in which the temperature in the upstream is higher than that in the downstream.Seepage velocity is the primary factor affecting the formation of the freezing wall of the cross passage,followed by the freezing tube diameter and refrigerant temperature,and the seepage temperature has less influence on the closure time.The upstream side wall is the weak area for the expansion of the freezing wall under seepage condition in which the temperature should be monitored intensively to track the formation process.
cross passageartificial ground freezingfreezing wallseepage flowtemperature field
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