FREEZING PROCESS.
The presence of water has always been the great obstacle in foundation work and in shaft sinking, and it is only comparatively recently that any one thought of transforming the liquid soil into a solid wall of ice about the space to be excavated. The method of doing this consists in inclosing the site to be excavated, by driving into the ground a number of tubes through which a freezing mixture is made to circulate. These consist of a large tube, closed at the lower end, inclosing a smaller one, open at the lower end. The freezing mixture is forced down the inner tube, and rises through the outer one. At the top, these tubes connect with a reservoir, a refrigerating machine, and a pump. The freezing liquid is cooled by an ice-making machine, and then forced through the tubes until a wall of earth is frozen around them of sufficient thickness to stand the external pressure, when the excavation can proceed as in dry ground.
This method was invented by F. H. Poetsch, M. D., of Aschersleben, Prussia, in 1883. The process has been used many times in sinking shafts in mining operations. "Shaft Sinking in Difficult Cases" by J. Reimer, translated from the German by J. W. Brough 1907, gives a list of 64 examples, most of which are in Germany and France, only one being in the United States. On shaft has been sunk by this process 816 ft., and several have been sunk over 300 ft. The Transactions of the American Society of Civil Engineers, Vol. LII, pages 365-450, contains an illustrated resume of the literature of the freezing process to February, 1904, and also a discussion of the same.
This process seems to have been valuable for sinking shafts through quicksand and other water-bearing soil under difficult cir cumstances, but has not been applied in foundation work.