Sometimes, in sinking a shaft through quicksand, the water runs in faster than any ordinary mode of drainage will remove it. M. Triger, an ingenious Frenchman, invented a machine by which the water could be pumped out. The cylinders of iron were five or six feet in diameter, and he divided them into three compartments, as nearly air-tight as possible. He forced compressed air into the lower one, and enclosed the workman inside. The man was thus in a sort of diving-bell. The compressed air, being forced against the bottom of the shaft, prevented the great mass of water from filtering through the sand. The small quantity which filtered in was, by the force of the compressed air, driven through the sand pipe communicating with the surface. “Imagine an army of mice,” the inventor graphically said to M. Simonin, “and a cat suddenly to make her appearance, and you would have the picture of water reaching the bottom of our shafts through a thousand holes in the ground, if the presence of the air is lowered, and returning suddenly to the surface as soon as the air recovers its tension.”
The rubbish and running sands are removed in buckets by hand, or by means of a rope passing through a pulley. Trapdoors communicate from one stage to the other, by means of which the buckets are removed without any serious loss of the compressed air. Shafts may be sunk through quicksands in this way to a depth of eighty or one hundred feet without difficulty. The laborers who pass their time in the compressed air work as easily as in the open atmosphere. Some of them, however, cannot remain there long, especially if they have the drum of the ear very delicate, or are in the habit of drinking to excess. The pressure of air in the chambers rarely exceeds three or four atmospheres.
This apparatus is frequently used for laying the foundation of bridges in the beds of rivers, where there are deep quicksands. The famous bridge of Kehl, near Strasbourg, was constructed in this way, and the engineers say that without some such apparatus the construction of the bridge would have been impossible.
If a shaft has been sunk and properly supported,—that is to say, timbered or walled,—it is generally divided into compartments. The shafts are generally from fifteen to twenty feet in diameter, and consequently there is plenty of space for dividing them. One of the compartments will serve for the tubs, cages, or buckets, in which the coal is raised. Another is for pumps to draw off the water, and sometimes where the miners go up and down by ladders a compartment is made especially for them.