Thermal-Mechanical Couping Law In Freezing Reinforcement Of Connecting Passage Between Guangxi University Station And Xinxiu Park Station

The artificial freezing technology is widely used in underground engineering due to its environmentally friendly construction environment,and wide applicability.This article combines numerical simulation with actual measurement data to study the frozen reinforcement project of the 2# connecting channel in the Xin Guang section of Nanning Metro Line 5.The reliability of the numerical model is verified by comparing the simulation results at the temperature measurement points with the actual measurement data and comparing the results of the designated cross-section and empirical formula calculations.Researching on thermomechanical coupling law in freezing process,excavation process and thawing process,And carry out the sensitivity analysis of soil thermal-mechanical coupling.the main research results can be summarized as follows:(1)The numerical simulation results are basically consistent.The calculated thickness of the frozen wall is 2.2 meters,which meets the design requirements and is on the safe side.At a depth of 20 meters,the maximum displacement occurs at the crown,and it rapidly decreases with increasing distance from the frozen pipe.This mainly occurs during the early stage of freezing,and produces a vertical displacement of about 4mm on the ground surface.Horizontal displacement does not affect the ground surface,but produces a large horizontal displacement inside the excavated soil.(2)Compared to excavation without freezing,excavating after freezing can effectively reduce settlement,which reflects the reinforcing effect of freezing method on the soil.The settlement during excavation decreases rapidly in the early stage of freezing and slows down in the later stage of freezing.After freezing and excavation,the shear stress increases and is concentrated inside the frozen zone.(3)During the natural thawing process,the diffusion of cold energy will increase the affected area of the low-temperature soil.Compared with the freezing process,the settlement range caused by thawing is larger.75% of the settlement occurs during the20-60 days of thawing,mainly due to the thawing of soil below-10℃.The slow melting process of soil below-1℃ does not have a significant impact on the ground surface.(4)The sensitivity analysis results show that changing the thermal conductivity does not alter the temperature trend at each temperature measuring point,but only affects the rate of temperature decrease.Changes in thermal conductivity have a limited impact on the temperature measuring points inside the frozen curtain,but have a more significant impact on the inner and outer sides of the frozen wall.At a depth of 20 meters,changes in thermal conductivity have almost no effect on the ground surface,and it can be considered that the freezing method has universality for soil with different thermal conductivity.Changing the cooling plan has a significant effect on the temperature field.The temperature at each measuring point gradually shows significant differences between 15-20 days of freezing.The higher the final temperature of the cooling plan,the smaller the vertical displacement and the larger the affected area.The soil can be quickly frozen by reducing the temperature of the brine to control frost heave.