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

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СКАЧАТЬ of groynes and ticklish work improving the harbour channel. However, we just managed; but it made me feverish, and I expect the blades, if they could be seen, are not exactly as when they left the foundry; but there, there is a good deal in pilework that has to be taken on trust, it is not like a foundation you can see and walk upon if so minded. Still, screw piles are all right for some soils, but I like disc piles better for sand, those that sink by water-pressure I mean. I don't think there is the same fear of the disc being broken as there is in the case of the screw, and the sinking is so easy and soft that no parts get strained as in screwing, but the ground must be soft, or there may be a bother.

      "After this shave from being bowled out, I always took care to dodge in a short one, now and then, when I knew the ground must be right, and I never got scared again. It was lucky, too, that a good many of the lengths varied, as on most jobs they are all the same, except the making-up lengths, and then down they all have to go unless a whole length can be left out when a seam of hard soil is reached, and that is not often the case, and there is not much chance of a bit of 'extras' that way on the quiet. I have known the game of 'extra' profit carried to breaking off a screw blade purposely, but I draw the line before I come to that."

      "Do you? I should not have thought it, as you don't mind cutting off the heads of timber piles, so you have promised to tell me."

      "That is a different material and consequently requires different treatment. You understand? Let me also tell you, I once heard a big Westminster engineer say, 'Timber we understand, iron we know a good deal about, and steel also; but we have plenty to find out yet both in the manufacture and use of nearly all metals,' or something like that, he said.

      "I acted up to that; and always say to myself, We understand timber, and know how to treat it‌—‌and so I don't mind cutting it, as I know what I am about with it, although I represent unskilled more than skilled labour. Metals are different goods, and it wants skilled labour to tackle them nicely."

      "There you are right."

      "Yes, different goods. So, following the lead of the engineer, I leave the iron piles as delivered, as we have yet something to learn about the metal; and things that I don't know much about I avoid as much as possible, and consequently there are good grounds for getting in some short lengths as occasion offers, just to have as little to do with the material that you don't know much about and that is a bit mysterious in its behaviour. So I lessen the handling of it, and shorten the lengths, and so increase the odds against the chance of it not turning out as one thought it would; and I ought to be thanked for it, I consider. You look a bit puzzled. I tell you, you are getting thick, and want fresh pointing up to sharpen you. Listen to me. Now, suppose you buy a dozen eggs, and you think and know, on the average, at the price two are bad; you take one away and find it's bad, then you have 11 to 1 odds as against 12 to 2 or 6 to 1, and there can't be so much chance of another bad one turning up so quickly. If you don't understand my meaning I can't make you. There may or may not be a different application of explaining the egg business, but mine is what I mean you to take, and I don't intend to bother about any one else. You are younger than I thought you were, or your brain is all of a tangle."

      "Wait a minute. All right. I understand now; you lessen the chances of failure and the extent of it when it occurs by having a little less to do with goods that are made of material no one seems to knows everything about."

      "Now you have it. Shake fins. Glad we have worked on to the right road again, as it looked like a collision just now."

CHAPTER III.

       Table of Contents

      SCREW PILES.

      Details.

      "Now for some details.

      "Solid piles are usually from 4 to 8 inches in diameter, and hollow cast-iron from 10 to 30 inches, and generally 10 to 20 inches. Avoid any cast-iron screw piles that are less than half an inch in thickness. When they are from 1/12th to 1/18th of the diameter is perhaps the best, according as their length is little or great; but of course they have to be of a thickness that will stand the load, and what is the best foundry practice should not be forgotten.

      "Now as to the blade of the screw. If of wrought-iron, which seems to me the wrong material for that purpose, it should not be less than half an inch in thickness; if of cast-iron, as usually is the case, the thickness of the blade of the screw at the pile shaft should be about 1·25 to 1·50 that of the column, and at the edge not less than half an inch, and it should taper equally on both sides, and care be taken that the metal is the very best and so cast as to ensure uniformity and strength.

      "All sizes of screws from twice to six times the diameter of the pile when hollow I have screwed, but the best are from 2 to 1 to 3 to 1, and when they are more than 4 to 1 it is to be feared they will break before they can be made to penetrate far enough to say nothing about. Solid piles with screws four to seven times the diameter of pile I have also fixed, and 5 to 1 to 6 to 1 is quite large enough; but the kind of ground and the depth to which they must be got down should govern the size and the pitch. The greatest depth, apart from imagination for measurement, to which I have ever screwed a pile is about 25 feet. Without special tackle I have made a 2 feet in diameter screw penetrate hard clay, dense sand, and other hard soil from 8 to as much as 17 feet; but then 10 to 15 feet is deep enough, for there is such a thing as overscrewing. A 3 to 4 feet in diameter screw I have fixed all depths from 10 to 20 feet in ordinary sand, clay, and sandy gravel. A 4 feet to as large as a 5 feet screw, which great size should only be used for soft soils, from 15 to 25 feet, and the most usual depth is about 15 feet, and hardly ever above 20 feet.

      "A 9 feet 6 inches screw blade has been used on a 7 feet in diameter cylinder, but that is the largest I have heard of, but then it only projected 2 feet 6 inches beyond the column. Five feet is usually about the largest, and is only used for very soft soils. When more than that size they are unwieldy and very liable to be broken, and if the screws are fixed to a shaft and have to be shipped they are awkward things, and the freight becomes expensive. For hard soil, and that which will not compress nicely, about 2 to 3 feet is large enough for the diameter of the screw, and 3 to 5 feet for soft soils. The pitch of the screw is generally from one-third to one-seventh of the outside diameter of the blade. It varies according to the hardness and softness of the ground and is steeper as it becomes harder. When the pitch is increased the effect of the power applied to screw it is reduced, therefore the steeper or greater the pitch the harder the screwing.

      "Piles can be screwed with a small pitch when sufficient power cannot be obtained to make a steep-pitched screw penetrate. Piles with a single turn of the screw, it seems to me, are the best, although the double-threaded screw may be right in soft marshy ground; but the usefulness of a double thread is doubtful, for I believe it breaks up the ground for no good, although some state that the screw threads work in parallel lines, and that a double-threaded screw is steadier; for they say a single-threaded pile is always likely to turn on the outside edge of the blade, and that the double-threaded is not, as it has a lip on both sides.

      "Generally the screw has rather more than one entire turn round the pile, and when it is below the ground each side of the blade steadies the other, for the turns range from one to about two. Sometimes the edge of the blade is notched like a saw; but it is a question whether the saw-edge blade will screw into ground that an ordinary blade will not, and until it is proved by experiment it can only be a matter of opinion; but there is one thing to consider, a saw-cut edge blade may to some extent wedge the soil between the teeth; still, I have used them, and they penetrated thin limestone, chalk, and compact gravel seams. Instead of double threads, double points are the thing, and all screw piles should have a point of some kind. For soft ground, a single gimlet, and a double for hard soils, and I have noticed what СКАЧАТЬ