Comprehensive Review of Artificial Ground Freezing Applications to Urban Tunnel and Underground Space Engineering in China in the Last 20 Years

Artificial ground freezing (AGF) has been applied widely in the construction of urban transportation infrastructure in China for the last two decades. This study provides a comprehensive review of the regional application, distribution, new developments, existing problems, and challenges of AGF. The innovative achievements of AGF in theory and technology are presented using selected prominent or typical engineering examples. Accidents or problems occurring in previous projects and the engineering risks of AGF technology were analyzed. In addition, the competition and integration of AGF technology with other construction methods are discussed. Furthermore, future research needs, including freezing tube installation issues related to directional drilling, miniaturization of construction equipment, artificial intelligence, information technology, and construction safety, are proposed. Finally, the expectations of AGF technology in urban development are predicted based on the new policies of urban groundwater protection issued in recent years. (C) 2022 American Society of Civil Engineers.