The application of intermittent freezing operation for improving the cost-effectiveness of artificial ground freezing projects

The Artificial Ground Freezing (AGF) technique is widely used in underground projects. Its application is very effective in meeting the needs of ground and structure support, while ensuring resistance to seepage flow during the construction process. During the freezing stage, most AGF projects require a large amount of energy to form and maintain the frozen curtain, resulting in significant costs. In this paper, the Energy Utilization Rate (EUR) and total energy consumption are considered the criteria for assessing the cost-effectiveness of AGF projects. The calculations of EUR require recording the variation of the volume of frozen soil, which is obtained from the simulation results of a numerical model that considers the heat transfer and ice-water phase change in frozen soil. The numerical model is based on back analysis of an AGF project. After validation, a sensitivity analysis of two freezing operations (continuous freezing and intermittent freezing operations) on EUR and energy consumption was conducted. The results reveal that the application of intermittent freezing operation can improve the cost-effectiveness of AGF projects effectively. For the specific 45-day AGF project that was studied, switching the freezing method from continuous freezing operation to intermittent freezing operation saved a total energy consumption of up to 2.6 ×10^7 kJ (a 13% energy-saving rate). At the same time, it can be seen that a proper intermittent freezing operation is capable of improving the EUR by up to 5% over the same period.