Computational modelling of artificial ground freezing in mechanized tunnelling

An advanced processes-oriented computational model for mechanized tunnelling has been extended to consider ground improvement by employing artificial ground freezing during the tunnel construction and excavation process. A numerical study is presented, in which the numerical simulation of the tunnel drive through a frozen ground is performed. The model considers the thermo-hydro-mechanical behaviour of the frozen ground and is capable of simulating tunnel advancement with mutual interactions between all relevant components, In this paper, the influence of the heat source induced by the TBM on the frozen ground during tunnel construction and the TBM advancement process is investigated numerically. The application of mechanized tunnelling in conjunction with the soil freezing method, however, represents a challenge due to the complex thermo-hydro-mechanical interactions between the frozen and unfrozen surrounding soil and the advancement process of the tunnel boring machine (TBM). The novel process-oriented model for mechanized tunnelling is capable to drive through the frozen and unfrozen ground. The first simulation stage consists of the stabilization of the ground employing artificial ground freezing. The second stage considers the simulation of TBM advancement through unfrozen and frozen ground, and the study of the influence of the TBM as a heat source on the frozen ground. The effect of hygro-thermo-mechanical interactions during machine driven tunnel excavation through a portion of soft soil strengthened by artificial ground freezing has been analyzed numerically. The exposure time is related to the speed of advance of the TBM or the standstill time at a specific position.