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Soil freezes naturally all of the time. It is at this point that dirt work usually stops.

Occasionally soil is intentionally frozen to improve its structural properties. This process has been used notably in Boston's Big Dig and the Fukushima Daiichi nuclear plant.

When soil is intentionally frozen so that tunnels or vertical shafts can be excavated, the structural properties of the frozen soil are important. It would seem logical that the frozen water would help to stiffen the soil, but how are the actual structural properties of the soil determined?

  • Do all frozen soils end up with the same properties? i.e. the presence of ice controls the properties.
  • Are the frozen soil properties related to the unfrozen soil properties in any way?
hazzey
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2 Answers2

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I don't believe there is any fundamental difference between intentionally frozen and naturally frozen soils. Other than control of the temperature.

I'm afraid the mechanics of soils (frozen or otherwise) is complex and depends on many factors such as the soil type, water content, grain-size distribution, compaction, etc. The soil properties used for design purposes are generally obtained through a combination of testing and empirically derived relationships. I don't think it would be appropriate for me to attempt to summarize the entire subject here. If you would like to know more details, this MIT OpenCourseware course may be helpful: MIT - Soil Behavior

With regards to your question specifically about frozen soils. Every soil will have different properties when frozen depending on the unfrozen properties as well as the temperature, ice content, porosity, etc. Your intuition that the frozen soil will be stiffer than the unfrozen soil is correct. Frozen soil can be 10-100 times stiffer than the unfrozen soil 1.

This book deals entirely with the design of frozen soils, including a chapter on Construction Ground Freezing, which was what you were inquiring about:

  • Frozen Ground Engineering (Second edition). Orlando B. Andersland and Branko Ladanyi. Chichester: John Wiley & Sons. 2004.

1 Yershov, E. D.. General Geocryology. Ed. Peter J. Williams. 1st ed. Cambridge: Cambridge University Press, 1998.

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atom44
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  1. take core sample
  2. stick in freezer
  3. run tests
  4. ?
  5. profit!

One important factor is the water content of the soil, freezing dry sand won't do much compared to freezing a waterlogged riverbank.

ratchet freak
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