Research On The Development Of Freezing Temperature Field Of Cross-river Channels In High Permeability Strata

The artificial freezing method is widely used in the construction of urban subway connection channels because of its characteristics of water stopping,high frozen soil strength and adaptability to complex strata.Artificial formation freezing is an extremely complex heat exchange process.In the face of some formations such as high permeability,rich water,and high water pressure,it is very easy to face freezing design problems and cause adverse effects.In view of this,this paper uses a combination of theoretical calculations,numerical simulations,in-situ tests,and field tests to conduct a comprehensive study of the cross-river communication channels in high-permeability strata.The main work and results of this article are as follows:(1)Theoretical analysis of freezing parameters,freezing wall thickness and freezing wall average temperature,combined with the heat transfer theory of porous media and the law of conservation of heat,obtain a coupled mathematical model of freezing temperature field and moisture migration.(2)For the on-site in-situ model test,the single-hole,double-hole and three-hole freezing temperature fields and their longitudinal and horizontal temperature expansion rates are analyzed,and the advantages and disadvantages of the double-hole freezing and three-hole freezing horizontal and vertical temperature expansion rates are compared.Analyze the limit radius and development rate of the frozen wall and the development law of the average temperature of the frozen wall.The results show that both the longitudinal and lateral temperature expansion rate are accelerated with the increase of the number of frozen holes,and the lateral temperature expansion rate between the three is faster than the longitudinal direction.When single-hole,double-hole and triple-hole are frozen,the limit thickness of the frozen wall is 0.96 meters,1.73 meters and 2.8 meters respectively,and the difference between the two is 0.77 meters and 1.07 meters respectively.In the double-hole freezing and the three-hole freezing,the lowest average temperature of the freezing wall drops to-8.1 ?,-11.6 ?,and the temperature difference is 3.5 ?,which shows that thedouble-row tube freezing has obvious advantages.(3)In order to study the freezing temperature field and related thermal parameters of the cross-river connection channel in high-permeability strata,the numerical analysis of the in-situ freezing test is carried out.The simulation results show that the used fluid-heat coupling finite element simulation is consistent with the actual freezing temperature field law,and The error does not exceed 5%,indicating that the numerical simulation can reflect the development law of the temperature field during the actual three-hole freezing process.(4)Based on the numerical simulation of the in-situ freezing test,the finite element analysis model of the thermal coupling of the cross-river connection channel in high-permeability strata was established to analyze the development law of the thermal coupling freezing temperature field of different cross-section flows,and the comparative analysis of the frozen wall under the conditions of seepage and static water Variation of thickness and average temperature of frozen wall.The comparison results of the model show that the seepage conditions of the three sections are thinner by 0.15 meters,0.18 meters,and 0.12 meters than the static water conditions,and the average temperature of the frozen walls rises by 1.6?,2?,and 1?,respectively,indicating that the middle of the communication channel is affected.maximum.Based on the above,attention should be paid to the development of the frozen wall at the upstream position of the seepage channel in the high permeability formation.When the permeability coefficient is above 45m/d,the upstream of the seepage channel of the seepage channel needs to be refilled to shorten the spacing of the frozen pipes and increase the size of the frozen pipes.Other measures,and pay attention to the design of the freezing upstream of the seepage to ensure that the average temperature of the freezing wall is below the relevant regulations.