The International Information Center for Geotechnical Engineers

Ground Freezing

 

5.0 ADVANTAGES AND DISADVANTAGES OF GROUND FREEZING

 

The following sections describe typical advantages and disadvantages of utilizing AGF.

 

5.1 ADVANTAGES

 

Ground freezing is an extremely versatile method for temporary ground improvement or cutoff.

It is applicable to the entire range of soils, provided that the soil is near saturation or completely saturated.  If water contents are not acceptable, water can be added, provided the water will not drain out of the soil quickly (Schmall and Braun 2006).  In addition to being applicable to the entire range of soils, it is also applicable to difficult ground conditions including large boulders and cobbles, or debris-rich non-engineered fills.  A good example of the applicability of ground freezing is demonstrated in the Boston Central Artery/Tunnel (CA/T) project, discussed later in this report in the Modern Applications to Civil Engineering section.

 

Additionally, ground freezing can create cutoff walls or frozen soil masses in a variety of geometries (shown in Figure 8), simply by modifying the placement and spacing of the freeze pipes.  This is especially important during tunneling applications, where freeze pipes are installed horizontally and at various angles to create stable frozen ground for tunnel support and excavation.  

 

frozen barrier configurations.PNG

Figure 9. Examples of frozen barrier configurations (wall, enclosure, solid block) (Wagner and Yarmak 2012)

 

Furthermore, ground freezing will likely be cost effective when the site conditions are such that stability and/or containment must be achieved with multiple methods, which combined have the same effect as applying ground freezing alone.  Again, the Boston CA/T project was one such project that determined ground freezing was the most cost effective solution using a value engineering process.  

 

5.2 DISADVANTAGES

 

Ground freezing is a highly energy intensive process, requiring refrigeration of massive quantities of soil over extended periods of time, which is very expensive.  Costs only increase if liquid nitrogen is required for quicker soil freezing.  

 

Additionally, implementing ground freezing requires plenty of monitoring: brine temperatures, soil temperatures, deflections of adjacent or nearby structures, heaving and settlement at the ground surface, groundwater salinity, pressures within freeze pipes (leak detection), frozen wall thickness, and the location and dimensions of possible windows within the frozen wall, among other site specific measurements.  

 

Possible failures of an AGF project can occur as a result of inadequate monitoring or installation.  The spacing of the freeze pipes may be such that the frozen wall barrier is not complete, leaving windows of unfrozen soil, or such that the frozen wall thickness is not controlled, and grows too large, placing unnecessary stresses on nearby structures and soil.  Additionally, improper securing of freeze pipes may cause leakage of the brine.  

 

Furthermore, there is the inherent disadvantage of the volume expansion of water during freezing, leading to soil heave and thaw settlement, which may damage adjacent or nearby structures if not monitored and accounted for with regular structure maintenance.  Soil heave and settlement may also damage AGF equipment, most commonly the freeze pipes, causing leakage and requiring maintenance. In cases where significant settlements could damage overlying or embedded structures, care is taken not to freeze ground beneath the structures as to avoid settlements upon thawing.

 

 

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