Study On Thrawing Styles And Laws Of Artificial Horizon Freezing Wall In Shield Starting And Arriving Construction

Tunnel end reinforcement is an important part of arriving and starting of shield machine technology in shield tunnel construction. Whether the soil reinforcement is successful of not is related to the security of arriving and starting of shield machine. Thus it is an important step of successful shield tunnel construction to choose a tunnel end reinforcement appropriately. Artificial freezing is a soil reinforcement method with flexible format, strong adaptability, no pollution, limit influence. It is more reliable and security in construction of shield arriving and starting. However, influence to surrounding environment caused to settlement during frozen soil melting period is a problem of artificial soil freezing. Thus mastering the temperature field law during the nature thawing or adopting artificial thawing method to shorten thawing cycle is necessary for controlling settlement by grouting.The thawing styles of artificial freezing soil are introduced in the essay. The principle and mathematical model of nature thawing and artificial thawing is proposed. Base on this nature and artificial thawing numerical models are set up separately used finite element software to calculate temperature field and analysis the factors'sensitivity. Apply on artificial horizontal freezing reinforcement for the north shield arriving in Ji Tsing-men station of line two Nanjing metro measure study in site is carried out. Laws of artificial freezing nature thawing temperature are got. Measuring and calculating results are compared. Artificial thawing technology and parameters are raised regarding on these.According to experiment of thawing settlement and consolidation coefficients, artificial thawing displacement field under difficult temperature circulating hot water is compared to the nature thawing.In conclusion, artificial horizontal frozen soil wall for the north shield arriving in Ji Tsing-men station of line two Nanjing metro have a long nature thawing period. Nature thawing time will be extended with the increase of thermal conductivity and latent heat and shortened with the increase of volume thermal capacity. It is more beneficial to shorten the thawing period with higher environment temperature in tunnel and higher initial ground temperature. It may greatly shorten the thawing period of artificial frozen soil by using the artificial thawing method. Artificial thawing period of frozen wall can be effectively shortened by raising temperature of circulating hot water, prolonging circulation time and shortening the distance of thawing pipes.