Water Supply: the Present Practice of Sinking and Boring Wells / With Geological Considerations and Examples of Wells Executed

by Ernest Spon

[CHAPTER IV.]
WELL BORING.

The first method of well boring known in Europe is that called the Chinese, in which a chisel suspended by a rope and surrounded by a tube of a few feet in length is worked up and down by means of a spring-pole or lever at the surface. The twisting and untwisting of the rope prevents the chisel from always striking in the same place; and by its continued blows the rock is pounded and broken. The chisel is withdrawn occasionally, and a bucket or shell-pump is lowered, having a hinged valve at the bottom opening upwards, so that a quantity of the débris becomes enclosed in the bucket, and is then drawn up by it to the surface; the lowering of the bucket is repeated until the hole is cleared, and the chisel is then put to work again.

[Fig. 49] is of an apparatus, on the Chinese system, which may be used either for hemp-rope or wire-rope, and which was originally made for hoop-iron. At A, [Fig. 49], is represented a log of oak wood, which is set perpendicularly so deep in the ground as to penetrate the loose gravel and pass a little into the rock, and stand firm in its place; it is well rammed with gravel and the ground levelled, so that the butt of the log is flush with the surface of the ground, or a few feet below. Through this log, which may be, according to the depth of loose ground, from 5 feet to 30 feet long, a vertical hole is bored by an auger of a diameter equal to that of the intended boring in the rock. On the top of the ground, on one side of the hole, is a windlass whose drum is 5 feet in diameter, and the cogwheel which drives it 6 feet; the pinion on the crank axle is 6 inches. This windlass serves for hoisting the spindle or drill, and is of a large diameter, in order to prevent short bends in the iron, which would soon make it brittle.

Fig. 49.

In all cases where iron, either hoop-iron or wire-rope, is used, the diameter of the drum of the windlass used must be sufficiently large to prevent a permanent bend in the iron. On the opposite side of the windlass is a lever of unequal leverage, about one-third at the side of the hole, and two-thirds at the opposite side, where it ends in a cross or broad end where men do the work. The workmen, with one foot on a bench or platform, rest their hands on a railing, and work with the other foot the long end of the lever. In this way the whole weight of the men is made use of. The lift of the bore-bit is from 10 to 12 inches, which causes the men to work the treadle from 20 to 24 inches high. Below the treadle, T, is a spring-pole, S, fastened under the platform on which the men stand, the end of this spring-pole is connected by a link to the working end of the lever, or to the rope directly, and pulls the treadle down. When the bore-spindle is raised by means of the treadle, the spring-pole imparts to it a sudden return, and increases by these means the velocity of the bit, and consequently that of the stroke downwards.

This method has been generally disused, iron or wood rods substituted in the place of the rope, and a variety of augers and chisels instead of the simple chisel, with appliances for clearing the bore-hole of débris. [Figs. 50 to 56] show examples of an ordinary set of well boring tools. [Fig. 52] is a flat chisel; [Fig. 53] a V-chisel; and [Fig. 54] a T-chisel. These chisels are made from wrought-iron, and when small are usually 18 inches long, 2¹⁄₂ inches extreme breadth, and weigh some 4¹⁄₂ lb.; the cutting edge being faced with the best steel. They are used for hard rocks, and whilst in operation need carefully watching that they may be removed and fresh tools substituted when their sides are sufficiently worn to diminish their breadth. If this circumstance is not attended to the size of the hole decreases, so that when a new chisel of the proper size is introduced it will not pass down to the bottom of the hole, and much unnecessary delay is occasioned in enlarging it. In working with the chisel, the borer keeps the tiller, or handles, in both hands, one hand being placed upon each handle, and moves slowly round the bore, in order to prevent the chisel from falling twice, successively, in the same place, and thus preserve the bore circular. Every time a fresh chisel is lowered to the bottom it should be worked round in the hole, to test whether it is its proper size and shape; if this is not the case the chisel must be raised at once and worked gradually and carefully until the hole is as it should be. The description of strata being cut by the chisel can be ascertained with considerable accuracy by a skilful workman from the character of the shock transmitted to the rods.

When working in sandstone there is no adherence of the rock to the chisel when drawn to the surface, but with clays the contrary is the case. Should the stratum be very hard, the chisel may be worn and blunt before cutting three quarters of an inch, it must therefore be raised to the surface and frequently examined; however, 7 or 8 inches may be bored without examination, should the nature of the stratum allow of such progress being made.