Nonlinear Transient Analysis of Temperature Fields in an AGF Project used for a Cross-Passage Tunnel in the Suzhou Metro

Abstract

This paper examines the evolution process of the freezing curtain and the transition process of unfrozen water in an Artificial Ground Freezing (AGF) project used for a cross-passage tunnel in the Suzhou Metro, China. The focus of this study was on confirmation of the rationality of the freezing design on a weak silty clay layer, using a prognosis of the temperature development by numerical simulation and field monitoring. For the above purposes, basic mathematical techniques were employed to address the nonlinear transient thermal conduction problem considering the release of latent heat. The comparison analysis of the temperatures gained by field testing versus numerical simulation was performed to verify the accuracy of the numerical model. The results indicated that the formation of a stable freezing curtain with the design thickness required more time than the estimated active freezing period. The variation of unfrozen water volumetric content within the frozen fringe is normally exhibited as a process of increase and then decline until it vanishes, whereas there was a gradual and continuous increase near the frozen fringe. Although there was a deviation in the results between field monitoring and the numerical simulation, the general temperature curves from both methods were essentially consistent.