Scamping Tricks and Odd Knowledge Occasionally Practised upon Public Works. Newman John Philip

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СКАЧАТЬ 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."

CHAPTER IV.

       Table of Contents

      IRON PILES.

      Arrangement‌—‌Driving‌—‌Sinking by Water-jet.

      "Tell me what you have learned about iron pile fixing, same as you have promised me you will about timber piles."

      "Very well. Here goes, then; first a word as to iron piles generally.

      "Although a group of piles when properly strutted, tied, and braced have plenty of stiffness, if you have to deal with them singly they are never stiff, but they can be made steadier when getting them down by having two large pieces of wood with a half hole in them, something like the shape of the old village stocks, and by putting or lowering it at low water until it is bedded in the ground. It must be weighted though, so as to prevent it floating. It acts like a waling, and is useful when the ground is treacherous, and provided it is level.

      "From watching the behaviour of piles when doing repairs and at other times, I think it wants a lot of careful arrangement to be sure the load is acting equally on the whole group, or, as may be intended, on say a few piles, and straight down the centre of each pile, for it makes a lot of difference to the strain on them, and it is not easy to make them all take the load at once as wished. It wants a good deal of attention, and the piles are not unlike a pair of horses that are not matched and don't work together properly‌—‌kind of now me, now you business. Before finishing reference to driving and screwing, let me say all the parts should be properly fitted together at the works and numbered so that the putting up on the ground is easier and in order to be certain all the bolt-holes agree; and it is well to have the lengths interchangeable and all the same, except the making-up pieces, and all bolt-holes as well as the flanges should fit in every respect.

      "When columns rest on a masonry, brickwork, or concrete base the piles ought to have a ring or base-plate right round them to hold them tightly together. It lessens the pier being shaken, and saves the side pushing of the holding-down bolts. I heard an engineer say the weight of the pier above their ends should be not less than about four times any force that might tend to lift them. The anchor-plates should be well bedded upon a solid mass or the strain upon the pier may go in one direction, and that the one not wanted. Don't be afraid of bracing and strutting piles, the more of it the better. I don't think much of a single turn of a screw blade a few feet below the ground for taking a load, although some good for steadying purposes generally, because the bed may become scoured out below the blade and then the screw is no use. Therefore the depth of possible scour ought to be positively known before relying upon the blade for permanent support. A lot can be said as to the grouping of piles, whether in triangles or in rows. In a triangle, although the load upon the foundations is spread over a larger area, it does not give as much lateral strength as when the piles are placed in one row, and taking everything into consideration I think if I had six piles to put down I should not place one at the top of a triangle, two lower down, and three at the base, but have two parallel rows of three piles; besides it lessens the length of the struts and the bracing, and that is something, but, of course, each case requires to be treated in a special way, and I have noticed when doing repairs that if there are six piles fixed thus, ∴ in a triangle, the wind and other force acts principally upon the bracing between the parallel rows, and the pile at the point does not do much towards keeping the others in the right place; anyhow the bracing there does not seem to hold as tightly as it does between the parallel rows, and I have had to watch groups of them in storms, and when the sea has been high, and that is my opinion."

      "Now, as to fixing iron piles."

      "When the ends have to be placed in rock, which has sometimes to be done in shore pieces, 'jumping' the holes in more than about 2 feet of water is to be avoided, for if the water is not still the holes become filled with sand and drift, and you must not take the jumper out but keep on continuously making the hole. It is ticklish business, because sometimes the rock grinds the jumper, and then the wings and point wear away. Occasionally they have to be worked inside a cylinder by ropes, rods, and gearing fixed in it, the cylinder being movable and held from the end of the part of the pier that is finished, but where the water is deep the ends must be put in the rock in Portland cement by divers.

      "I have driven a good many iron piles with a ram, but you have to be careful, no matter whether the soil is sand, gravel, clay, or silt. I like a copper ring on the head of the iron pile and a good long timber 'dolly,' not less than 4 or 5 feet in length, and then the ram does not burst СКАЧАТЬ