Artificial Ground Freezing by Solid Carbon Dioxide – Analysis of Thermal Performance

Artificial ground freezing (AGF) is a ground improvement technique that is commonly used to create temporary earth support and groundwater control system during underground constructions (tunnels, shafts and mines). In the past two decades, solid carbon dioxide (SCD) has received increasing interest as a source of cold to freeze the soils. SCD provides a faster and safer solution to lower the ground temperature below the freezing point compared with alternative and conventional AGF techniques using refrigerants such as liquid nitrogen (LN). The existing analytical models for the design of AGF cannot provide accurate prediction of the SCD-based artificial ground freezing as they do not consider the specificity of heat transfer to the sublimated SCD. In addition, they neglect the thermal resistance due to the effects of the layers of freeze pipe, drilling mud and casting materials in the overall heat transfer. We present a new semi-analytical model for the formation of a frozen body during SCD-based ground freezing that takes into account the presence of additional sources of thermal resistance at the freeze pipe. The proposed model describes the formation dynamics of single-ice cylinders and plane ice-wall along with temperature distributions within the freezing mass and SCD consumption. The proposed model is tested against the known laboratory test results and alternative numerical models to demonstrate the accuracy of the solution for predicting all characteristics of ice-wall dynamics.