Scamping Tricks and Odd Knowledge Occasionally Practised upon Public Works

by John Newman

"How do you fix the capstan head to the pile shaft?"

"In many different ways. Sometimes it is keyed on or clamped tightly to the top of the pile length by steel wedges, also placed upon the pile length and fixed by temporary bolts passing through the top flanges of the pile length, and also by fixing a temporary ribbed pile into the capstan head, and by connecting it with the permanent pile by bolts or slots, and so wedging is not wanted and it can be raised and lowered. Another way is, two of the internal sides of the pile at top are cast flat for a foot or so down into which the capstan head fits, and the inside diameter is lessened for an inch or two to prevent the capstan head slipping down, but it generally can't do that, even without the narrowing of the pile for that object.

"As the capstan is subject to great wear and tear and sudden strain, it should be strong, for if it breaks the work is stopped. Wrought-iron capstan heads are used, but cast-iron are perhaps better. Sometimes the capstan sockets are made to fit the ends of rails, if rails instead of timber are used for the capstan bars, but rail bars are rather heavy and are not nice to handle. The capstan socket is generally made to receive from eight to ten or more radial lever arms, and the lengths of the bars are anything from 5 to 40 feet, but the latter is rather too long as it is very difficult to control the strain and the bar usually bends and springs. The best working lengths are from about 8 to 20 feet, if the staging is so large. The best height for the capstan bars above the floor stage is from 3 feet 6 inches to 4 feet 6 inches. The capstan bars have to be lifted and again fixed as the pile penetrates, or a temporary pile of different length has to be fixed in it, unless the capstan head can be slipped up and down on a ribbed pile, hence you may want a platform you can raise or lower easily when required. If you use double-headed rails of the same section top and bottom for the bars, you can have them bent up a little near the capstan head, and when you start, the bent end is lowest, and then the bars can be reversed and so the work proceeds.

"Put the men, horses, or oxen in the most natural position for exerting their full strength or a loss of power will result, and therefore it will cost more to screw the piles.

"Should there be gantry staging on the site, the piles can be pitched from a traverser, or by means of an ordinary crab winch. They can also be screwed from the permanent structure by means of a projecting stage temporarily fixed to it, and of a length sufficient to reach the next span. The pile is run forward upon rollers and placed in the right position. Then it is screwed on the endless rope system previously described, or by passing the rope round a deep groove in the capstan bar ends, and the rope is held tightly by being placed round a smaller grooved pulley fixed about a hundred feet or so back towards the shore. The men haul the endless rope and so the screwing is done. The worst of screwing by endless ropes this way is that the pile very probably may be pulled over towards the source of power as it comes from one direction, therefore, support is required on the side of the pile to prevent this tendency. The circumference of the ropes used varied from 4½ to 6 inches, but I have used a 10 inch rope. Small ropes are generally relatively stronger than large ones. Stretch a rope well before using, as it yields, especially hemp ropes. The distance between the point at which the power is applied, and the ground should be as little as possible. In firm sand, when the power has been more than about 20 to 25 feet above the ground, it is often very difficult to screw piles by ordinary means to more than a small depth, as two places in the pile are wanted from which to apply the screwing force, and both as low down as convenient; but in screwing from a second stage care should be taken that the pile shaft is not bent, for it may then be strained like a girder and not merely as a column, also when much power to screw is required it is not easy to avoid pulling them out of the vertical. Always screw them steadily and prevent jerking. Any obstruction, such as a boulder, tends to displace a pile, and loosens the ground around it. In soft soils it may be possible to pull piles upright by pushing aside an obstruction if the pile is given a turn or two after meeting it and before pulling; but it must be carefully done, or the pile may be smashed, and it is only safe to pull it over in easy soils and when much force is not required."

"How much power is generally wanted for screwing?"

"That is not so easily answered as asked. It varies very much, and, of course, depends upon the kind of soil and the size and pitch of the screw. Ten men may be sufficient and a single stage, but two stages may be necessary should the pile be 50 or 60 feet in length, and then not far from one hundred men. An engineer told me the force generally required for piles of usual sizes under ordinary screwing circumstances varies from about 8 to 10 tons to as much as 50 tons, and usually from about 10 to 25 tons, and, of course, the number of men to screw in proportion.

"Ordinary piles and screws have gone down 21 feet in sand in eight hours, and by steam machinery in clay at the rate of 6 inches per minute, and also, to my loss only about 1 foot in a day‌—‌and then it is time to stop altogether, should many piles hold like that. To compare what has been done with what has to be done is misleading unless the conditions are alike, for if they are otherwise the power required, cost, and rate of screwing will all be different. I have screwed a 6-inch pile with a 2-feet one-turn screw into 20 feet of ordinary sand with an applied power of 30 tons as calculated by an engineer from measurements and the force of men applied at the capstan bars. There is the surface friction on the screw blade and the pile shaft in the ground, the cutting of the earth by the edge of the blade and the points, and the loss of power from torsion and that applied compared with the effective force, slip, friction, &c., to consider; and the relative surface of the blades, width, and thickness of the cutting edge and the pitch‌—‌for a steep pitch means harder screwing. By using capstan bars and men at them, instead of ropes at the ends of the arms worked by crabs, you will find about one-fifth more power is gained, or rather is not lost. Of course, place the men as near to the end of the capstan bar as convenient for work. My lecture is finished, and I am parched."

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CHAPTER IV.