The International Information Center for Geotechnical Engineers

Ground Freezing




Artificial ground freezing is a versatile technique for ground improvement and stability.  The applicability of AGF covers most soil types including non-engineered fills, boulders and other large obstructions, and weak fine grained soils.  It has been used for vertical shaft construction for mining, stabilization of debris-rich earth fills, horizontal stabilization for tunneling, vertical and/or lateral contaminant containment, contaminant redirection, groundwater cutoff tied into bedrock, and emergency stabilization using liquid nitrogen.  

AGF creates an impermeable, frozen soil barrier or mass, which has higher strength and stiffness than the unfrozen soil.  This also has the capacity for soil heave and subsequent thaw settlements, which could become problematic for nearby structures.  Proper site characterization is key to anticipate the effects of ground freezing on the soils at a particular site.  Laboratory testing standards are available from both ASTM and JGS.  Classification standards for frozen soils are documented by ASTM.


AGF is implemented in the field using a mobile refrigeration plant, which circulates chilled calcium chloride brine through freeze pipes, removing heat from the soil and freezing the soil’s pore water.  Liquid nitrogen may also be used, however it is allowed to evaporate into the atmosphere rather than being recirculated.  A number of design considerations must be taken into account such as freeze pipe spacing, freezing time, groundwater velocity, saturation, pore water salinity, estimated soil heave, and costs.  Temperature of the soil and coolant, as well as soil heave, settlement, and pressures on existing structures as well as the freeze pipes are important to monitor while implementing an artificial ground freezing program.  Overall, artificial ground freezing has a wide variety of applications, and an history of successful application in the field.  It has become economically competitive with traditional ground stabilization methods and has the ability to be applied to a wide variety of projects.




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