Ground freezing is on way to control the inflow of water to a mining operation. If flow quantities are low, it may be easier to pump from dewatering wells, of from the mine workings themselves. If the climate and the rock are hot, it may be better to grout. But if you are in Canada or more northerly or southerly climes, freezing may be practical. The following are references to ground freezing:

  1. Controlled ground freezing for mining and construction applications has been in use for over a century. Despite the great technological evolution which has occurred during this period, it still remains more of an art than a science. (Link)
  2. The present ground freezing technology used worldwide by most ground freezing companies is based on quick freezing using circulating brine or, in some cases, liquid nitrogen. These methods are fast but very expensive and utilize large equipment with high electrical requirements.(Link)
  3. In any ground freezing scenario, the presence of flowing water can significantly delay or even prevent the development of ice due to heat addition by the moving water. (Link)
  4. The uncertainty of the pre-evaluation of potential ground water inflow rates in underground mines results in difficulty in planning and costing the water related activities of the mines. (Link)
  5. Ground freezing has been used by Cameco at the McArthur uranium mine in the Athabasca sandstone region in the northern part of the province of Saskatchewan, Canada. (Link)

Here are some companies that will undertake to freeze the ground at your mine or civil works – as always I recommend looking at these sites for the technical and engineering information as much as for the “marketing-stuff.”:

Some case histories of mines where ground freezing has been applied, or is planned:

And finally do not forget the Geo-Slope International software TEMP/W. Here is how they describe it: TEMP/W is a finite element software product for analyzing thermal changes in the ground due to environmental changes or due to the construction of facilities such as buildings or pipelines.

For fun and more information, see these sites:

Background to this technical discussion is the Cameco Cigar Lake mine. The premining-technical knowledge is set out by Barry W Schmitke (2004) in Cigar Lake’s Jet Boring Mining Method . To access the figures go to this link. Here are some extracts:

  • The Cigar Lake orebody is situated 430 meters below surface atthe unconformity between metamorphic basement rocks and flat lying sandstone.Major technical factors influencingthe mining method selection include ground stability, control of ground water (sic), radiation exposure and ore handling and storage.
  • Cigar Lake’s jet boring mining method involves several major steps: artificial ground freezing of the orebody and surrounding rock; TBM (tunnel boring) type development of access crosscuts below the orebody; installation of cased pilot holes upwards through the ore; and ore extraction using a rotating high pressure water jet within the pilot holes.
  • The cap [i.e., the clay above the orebody] is succeeded upwards by a highly heterogeneous, highly permeable zone from 20 m to 50 m thick consisting of variable soft to moderately indurated sandy clay, unconsolidated sand, and variably altered sandstone.
  • The deposit and area are highly fractured. Post-mineralization fracturing isthe dominant control of hydraulic conductivity and, where it transects the otherwise impervious claystone core ofthe deposit, fracturing acts as conduits for water, sand, and soft clay.
  • Two of the primary geotechnical challenges in constructing the test mine have been control of groundwater, and ground support in areas of weak rock.

The support of the weak rock associated with the oreboby and the minimization of the potential for a large inrush of water while mining the ore was addressed through ground freezing.