Fig. 117.
To equalize the pressure of water and gas behind the different sets of tubbing, pass pipes, Figs. [115] and [116], are sometimes used. Another expedient to effect this is to have a valve, working upwards, placed in the wedging crib, [Fig. 117]. A ball is also sometimes used, [Fig. 118].
The various modes of piercing beds of quicksand are;—By hanging tubbing to that already fixed, and adding fresh rings as the sand is removed. This is only practicable when the quantity of sand is inconsiderable. By heavily weighting a cylinder of iron of the same size as the shaft, and thus forcing it down through the sand. By keeping back the sand by the use of piles—a resource that can only be recommended when the bed of sand is not of great thickness. When the water is excessive, by using pneumatic agency. As these operations are apart from our immediate subject we need not further discuss them.
M. Chaudron’s system, which is a modification of Kind’s, is divisible into the following distinct processes, which consist of;—
The erection of the necessary machinery on the surface, and the opening of the mine.
The boring of the pits to the lowest part of the water-bearing strata.
The placing of the tubbing.
The introduction of cement behind the tubbing to complete its solidity.
The extraction of the water from the pits, and the placing of the wedging cribs, or “faux cuvelage,” below the moss box.