Assessing the reuse of liquid nitrogen in artificial ground freezing through field experiments

Liquid nitrogen is the most common refrigerant adopted in the artificial ground freezing (AGF) method for the rapid freezing of soil. However, the relatively high price of liquid nitrogen demands the reuse of liquid nitrogen in AGF, which utilizes partially gasified liquid nitrogen after an initial injection. This study investigated the reusability of liquid nitrogen in AGF by performing a field experiment. Temperatures of the ground were monitored near the sub-freezing pipes installed 1 m away from the main freezing pipes, where liquid nitrogen was initially injected. A frozen wall having a thickness of 1 m was formed between two sub-freezing pipes after 5 days of injecting liquid nitrogen into the main freezing pipes. Furthermore, the lowest temperature of  − 12 °C measured in the sub-freezing pipe implied that the temperature of nitrogen after circulating through the main freezing pipe was sufficiently low to freeze the surrounding soil formation. The freezing rate, elapsed time for freezing, and freezing duration evaluated from the monitored temperature data also demonstrated the promising potential of reusing liquid nitrogen in AGF for saturated silty deposits.