Performance and Analysis of Artificial Ground Freezing in the Shield Tunneling

Abstract

To prevent any possible accident as shield machines enter into vertical shafts from soil or exit from soil into vertical shafts, artificial ground freezing is often conducted to form perfectly watertight between diaphragm walls and the adjacent soil. This paper presents the mechanical performance of the artificial ground freezing applied to shield tunneling in the construction of the Taipei MRT system. Two case histories at the same site, one with installation of vertical freezing tubes and the other with horizontal freezing tubes, are presented. Over the ground freezing period the temperature of the soil in the frozen region was monitored through the automatic data acquisition system to ensure the temperature of the destined soil matching the original design requirement, i.e., below -1.0°C. Moreover, finite element analysis of temperature change over the period of ground freezing was carried out, in which the material parameters were determined with a reasonable procedure. Compared with the monitored results, the predicted values were in good agreement with the monitored ones. The numerical tool and procedure for determining material parameters are useful in predicting the temperature change during ground freezing.