Development of Ground Freezing Method Using Natural Refrigerants and Its Application

Abstract

This paper presents a newly developed ground freezing method in Japan. Instead of HCFC or HFCs, it uses NH₃ and CO₂ for freezing; both are natural refrigerants. Thanks to the use of natural refrigerants, the new method (CO₂ freezing method) is not only good for the environment but also more effective in ground freezing than the conventional method. The two fundamental experiments conducted to verify the effectiveness of the ground freezing by natural refrigerants, and the outlines and the results are shown in this paper. Moreover, the application of the CO₂ freezing method is also shown. The application was ground improvement work for shield tunneling at a depth of about 66 m, and the first use of newly developed flat-shaped perforated freezing pipes. Finally, the most recent experiment is introduced. It was a long-distance pumping experiment of CO₂ refrigerant, and its purpose was to expand the scope of application to respond to social demands in Japan for use of a great depth underground. The result proved that CO₂ refrigerant could be circulated in the distance of 1500 m from the plant to the freezing area, instead of about the typical 100 m.