Freezing of Soil
Freezing of Soil
the artificial cooling of soil in its natural bedding to subzero temperatures in order to reinforce it and impart to it the required water-impermeability. As a result, a solid ice enclosure (cofferdam) forms around the workings, preventing water or quicksand from entering them. Freezing is used in laying the foundations of buildings and structures and in the construction of shafts, subways, screens to prevent percolation of water, dams, docks, and underground storage areas, as well as to combat landslides. Freezing is the best way to stabilize water-saturated ground. It can be used at different depths, with different combinations of soil, and at different flow rates and degrees of mineralization of groundwater.
To create an ice enclosure, holes are drilled around the workings or foundation pit, and freezing columns and then feed pipes are lowered into the holes. Brine (a calcium chloride solution) cooled at a freezing station circulates in the columns. In the course of continuous heat exchange with the brine, the ground surrounding the column is cooled and frozen, forming ice cylinder’s around the columns. The cylinders gradually increase in diameter and meet, thereby creating a solid enclosure. Upon emerging from the freezing columns the brine travels through a collector to the freezing station, where it is again cooled by refrigerating machines of various capacities.
The following basic methods of freezing soil are distinguished: freezing with parallel or successive connection of holes, zone freezing, local freezing (from the face of the shaft), and stepped freezing.
New methods of freezing soil that have been developed in the USSR and are now used in constructing underground installations include brineless and air freezing, freezing in ground with running water, and horizontal freezing. Methods involving the construction of foundation ditches without timbering (using the frozen ground as enclosing structures), as well as the differentiated method of freezing soil, have been assimilated.
REFERENCESTrupak, N. G. Zamorazhivanie gornykh porod pri prokhodke stvolov. Moscow, 1954.
Trupak, N. G. Zamorazhivanie gruntov v stroitel’stve. Moscow, 1970.
Dorman, la. A. Iskusstvennoe zamorazhivanie gruntov pri stroitel’stve metropolitenov. Moscow, 1971.
IA. A. DORMAN