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Ground Freezing

Ground Freezing

Ground Freezing



Ground consolidation by means of freezing

Freezing as a method of soil immersed into water is a technique known for several decades in the field of geotechnical engineering. Ground freezing can be achieved by the direct (liquid nitrogen) or indirect method (brine). For both systems thermometric data points, placed inside thermometers distributed within the volume to be frozen, allow an indirect control on the formation of the frozen structure.

In the direct method, nitrogen (close to the atmospheric pressure is liquid at a temperature of about -196 ° C) circulates in closed metal pipes causing a thermal shock in the groundwater surrounding the tube itself. Using liquid nitrogen it is possible to freeze the pore water present in a cylinder of soil of about 1 meter diameter within 3-4 days. The liquid nitrogen is distilled from the air and is transported and stored on site in special refrigerated tankers. Once used, the nitrogen is dispersed into the air again as gas.

In the so-called indirect method, brine (a solution of calcium chloride in water) is cooled by means of an electric refrigeration (chilling) unit at temperatures of -35 ° -40 ° C and is circulated in metal tubes placed in the soil (freezing pipes) returning after to the chilling unit to be cooled. In this case it will take about 3-4 weeks to freeze the water present in a cylinder of soil of about 1 meter in diameter. Also in this case the circulating system must be closed, it is essential to avoid any leakage of brine into the ground.


Ground Freezing
October 2013 - March 2014

Second Warsaw metro Line. Mixed method ground freezing at station C13 Powisle underneath the Wislostrada Tunnel.

Ground Freezing
April 2014 - March 2015

Road Tunnel 1,1 km long and 11 m internal diameter crossing under the so called Dead Vistula river in the vicinity of Danzig (Poland).

Ground Freezing
May 2002 - May 2003

Twin Metro tunnel crossing under the main building of the Central Station of Leipzig in Germany.