[CHAPTER III.]
WELL SINKING.

Previous to sinking it will be necessary to have in readiness a stock of buckets, shovels, picks, rope, a pulley-block or a windlass, and barrows or other means of conveying the material extracted away from the mouth of the sinking. After all the preliminary arrangements have been made, the sinking is commenced by marking off a circle upon the ground 12 or 18 inches greater in circumference than the intended internal diameter of the well. The centre of the well as commenced from must be the centre of every part of the sinking; its position must be carefully preserved, and everything that is done must be true to this centre, the plumb-line being frequently used to test the vertical position of the sides.

Figs. 17, 18.

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To sink a well by underpinning, an excavation is first made to such a depth as the strata will allow without falling in. At the bottom of the excavation is laid a curb, that is, a flat ring, whose internal diameter is equal to the intended clear diameter of the well, and its breadth equal to the thickness of the brickwork. It is made of oak or elm planks 3 or 4 inches thick, either in one layer fished at the joints with iron, or in two layers breaking joint, and spiked or screwed together. On this, to line the first division of the well, a cylinder of brickwork, technically called steining, is built in mortar or cement. In the centre of the floor is dug a small pit, at the bottom of which is laid a small platform of boards; then, by cutting notches in the side of the pit, raking props are inserted, their lower ends abutting against a foot block, and their upper ends against the lowest setting, so as to give temporary support to the curb with its load of brickwork. The pit is enlarged to the diameter of the shaft above; on the bottom of the excavation is laid a new curb, on which is built a new division of the brickwork, giving permanent support to the upper curb; the raking props and their foot-blocks are removed; a new pit is dug, and so on as before. Care should be taken that the earth is firmly packed behind the steining.