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  Application of Liquid Air Refrigerant to Artificial Ground Freezing in Enclosed Subsea Tunnels

  Subsea tunnels are highly vulnerable to seawater intrusion caused by high water pressure during construction. The artificial ground freezing (AGF) will be a promising alternative to conventional reinforcement methods. Use of brine as a refrigerant is disadvantageous because of its longer freezing time due to the high boiling point. On the other hand, liquid nitrogen, which can freeze saturated soil formations more quickly, inevitably imposes a limitation that the evaporated nitrogen gas may suffocate the workers in enclosed environment such as long-span tunnels. In this paper, liquid air as a novel refrigerant is introduced to facilitate AGF, capable of rapid and safe freezing for constructing a subsea tunnel. In order to evaluate the feasibility of AGF along with liquid air, an optimum mixture ratio of liquid oxygen and liquid nitrogen was suggested, and the stability was verified in accordance with the pressure and flow rate. A lab-scale freezing chamber was devised to investigate a freezing process for sandy soil saturated in different salinity. In addition, the applicability of liquid air for rapid AGF was evaluated.

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