Numerical simulation of artificial-freezing propagation for subsea-tunnel construction: Effect of refrigerant temperature and ground water

When subsurface water pressure is highly excessive, generally observed in construction of a subsea tunnel, it is difficult to prevent water inundation even with jet-grouting. The artificial ground freezing technique has been rapidly developed in the past several decades as an alternative to such a highly performed grouting technique. The freezing process involves the circulation of a refrigerated coolant through a series of embedded pipes to convert soil water to ice, creating a strong and watertight zone (wall or ring). The design of a frozen earth barrier is governed by thermal properties of the soils and pore fluids, response to the freezing system, and groundwater flow around the cooling pipes. In this paper, the rate of freezing propagation and the freezing range were numerically simulated with consideration of the refrigerant temperature as a cooling boundary condition and the effect of groundwater flow to the frozen body shape. As a result of the simulation, it is found that the freezing rate and range are considerably influenced by the refrigerant temperature. In addition, the groundwater flow leads to an abnormal shape of frozen soil body and may alert the designer of artificial freezing to underestimating the dimension of cooling pipes.