Risk prevention and control of artificial ground freezing (AGF)

The artificial ground freezing method (AGF), a special construction method, has a history of almost 160 years. It is still a flexible, and reliable environment-protection geotechnical-support method to solve the three difficulties of groundwater, soft soils, and unpredictable deformation encountered in underground engineering. It is the core of AGF to freeze the water in stratum into ice by artificial refrigeration. However, it is the existence of ice that maintains the strength of frozen soils and leads to frozen soils being much more changeable and sensitive, which makes the AGF have some risks in engineering. In this study, the characteristics of artificial frozen soils and the corresponding risk of AGF engineering are elucidated based on the basic principles of the phase change process and dynamic balance of water in frozen soils, water migration during soil freezing, and the internal connection of frozen soils. Then, based on the AGF construction process, the risk prevention and control method of AGF are put forward from three aspects: strictly controlling the reliability of design input data, strictly controlling the quality of freezing system, strictly controlling the safe operation and maintenance during the whole processes of freezing and excavation, which will provide a new guidance for the application of the AGF in underground engineering construction in the future.