Field experiments for three freezing operation scenarios in silty soil deposits

Artificial ground freezing methods have been widely used in many engineering applications to change the mechanical and hydraulic properties of soil. Two freezing methods, open and closed systems, have been commonly utilized depending on the target freezing rate and budget of the project. In this study, a novel freezing pipe was designed, which enables the frozen soil to be formed in an elliptical shape to satisfy special construction demands such as tunneling projects. Temperature evolution of silty deposit in open and closed system were assessed respectively by injecting liquid nitrogen and circulating ethanol. In addition, the efficiency of hybrid freezing operation (open+closed system) in a silty deposit was investigated by injecting liquid nitrogen (open system) followed by the circulation of ethanol (closed system). The elapsed time for freezing and the freezing duration is also evaluated from the measured temperature data at distances of 25, 50 and 75 cm from the freezing pipe. The results show that the designed freezing pipe enabled forming a frozen soil in an elliptical shape. In addition, the hybrid freezing operation is an effective method for forming and sustaining a relatively large volume of frozen soil without continuously injecting liquid nitrogen.