Scamping Tricks and Odd Knowledge Occasionally Practised upon Public Works

by John Newman

"Piles can also be fixed in a medium depth of water by ordinary gantries, but if they are in the sea the road on the staging should be kept from 12 to 15 feet above high water on an open sea coast or the inclined struts and ties and rail tops as well are very likely to be destroyed, and it is also advisable to construct the flooring of the stage so that it can be easily taken away in case of storms. The stage piles also require to be well stiffened by struts, transoms, diagonals, and capping sills. I have screwed piles from a floor that has been suspended from staging by chains and ropes to the height wanted, and when lowered it was fixed temporarily and as many guides as possible were made for the piles. Perhaps as good a way as any is to fix, say four guide piles having a space between them a shade larger than the outside dimensions of the screw blade and braced to the rest of the stage, and after the screw is in position and ready for screwing in the ground, place, say a couple of frames, one at top and one as low as possible between the guide piles, about an eighth of an inch more than the outside dimension of the pile shaft, for then the pile is kept in its right position as it is screwed. The guide frames should be at about every 10 or 15 feet of the height above the ground, and at some point between the capstan level and the ground. Should it be a tidal river, fix guide booms if a properly made iron frame cannot be placed, and remember the more a pile is guided the easier it is to screw, and especially so at the start.

"The size and strength of the staging must be regulated according to the power available for screwing the piles, but the length of the lever arms and the capstan bars require a space in which to revolve, from, say, 35 to 60 feet square. No timber stage is immovable, for the wood yields. It is well to have two floors in a stage if it does not cost too much, and there is plenty of tackle and a lot of screwing to do; say, one fixed above high-water level and the other about half tide in order to obtain double power, and sufficient power to screw the piles cannot sometimes be otherwise secured. A word about floating stages. With them it is not easy to make a pile screw vertically unless the ground is uniform, and should a pile meet a boulder it will most probably be forced out of position. According to the power required‌—‌which really means the nature of the ground, as the harder the soil the harder the screwing‌—‌the form of the pile and the depth to which it has to be screwed, so must be the size and strength of the raft, pontoon, or lighter, and the moorings must hold it tightly. In some places a screw cannot be fixed from a floating stage, for the water may nearly always be too disturbed, and the pontoons may sway too much, for in all cases men, horses, or bullocks must have a steady footing, and screwing machinery also requires a firm base. Unless the moorings are very secure the platform will be unsteady. Its level should be as little above the water as practicable for work, so as to keep the point of resistance and that at which the screwing power is applied as near together as possible, and the lower the pontoon the less it rolls. It does not matter much what craft is used so long as it is broad and steady and not high, as a platform or deck must be made upon it in any case. To do any good with floating stages the power required should be little, and the ground soft and uniform, for sufficient force to screw may not be obtainable from a floating body, and in hard soil it may only be possible to screw piles a little way down and not to a sufficient depth for the load they will have to bear.

"Of course, vertical pile screwing is the easiest, and to try to screw them at a greater angle than 63°, or about ½ to 1, is unadvisable, and may not succeed, and even if they do it is too steep to be nice. 1 in 10 to 1 in 20 for raking piles is enough; for if they have to carry girder ends, the more the batter the greater the strain on the pile, and the same during screwing.

"Sometimes in loose soil it is difficult to start screwing, and then a good plan is to cast some clay or solid earth round the pitch; it steadies the pile and will probably make it bite properly, or a heavy weight placed on the pile may make it catch hold of the ground; if not, a few blows from a ram may do it. As a hollow pile penetrates, the core requires to be removed, so as to help it to descend. If it is not large enough for boys to get inside, scoops and tackle can be used. Water forced down makes sand boil round the screw blade, and when the pile is empty the unbalanced head of water outside relieves the pile and the screw blade from some of the surface friction. If water pressure cannot be used, the water inside the pile should be removed either by pumps or buckets so as to help to loosen the ground.

"Piles do not generally screw to the full pitch, but when a pile descends more than the pitch at the last turn, it can be considered the weight of the pile is too great for the ground. The slip usually increases according to the yielding or plastic nature of the soil, and the depth to which the pile is screwed. When water reaches such soils the slip is increased, but not perceptibly in sand and loose grained soils. Suppose the full pitch is 9 inches. The slip may be anything from about 1 inch to as much as 4 inches. By watching the way in which the screw penetrates, and whether it descends about the same distance each turn, or regularly decreases, it can be judged whether the bite of the screw is right. Some slip will generally take place, therefore note at first how much it is, and consider whether it will not churn up the ground, for if the screw blade turns on nearly the same lines, the bite will be gradually destroyed, and then it may be very difficult to obtain a fresh hold of the ground, and the pile will most probably not screw vertically, and the screw blade is liable to be injured and may become worn away considerably.

"Piles can be screwed by means of men, horses, oxen, and machines. Man-power can be used anywhere, machines in most places, but horses and oxen only on land when the piles are screwed on a foreshore or between tides; of course all live power works at the end of the capstan bars. Once I had the option of screwing by horses or oxen, and chose oxen. Another man had horses. I made more profit than he did, and the piles screwed easier than his. I did not let him come near me when screwing; but if you have the choice, use oxen in preference to horses. Of course, I am speaking of those countries where they are used to the yoke."

"Why?"

"Because they do not stop at any time or back like horses, not even when the resistance of the pile becomes too great without more power, but continue to pull, and therefore backward motion of the pile is prevented. The oxen were yoked to two cross-arms attached to the end of the lever.

"There are several machines for screwing piles worked by steam or other power, and when the ground is not easy to penetrate, and a large number of piles have to be screwed, their cost will be saved in the regularity, quickness, and ease in screwing, and in stiff soil by machine power I have known them screwed at the rate of 4 to 6 inches per minute. Of course, it is a special machine, and not easily sold when not further wanted except at a much less price than has been paid for it, and that has to be considered. There are several different methods of screwing piles from a fixed stage; for instance, suppose a pile of sufficient length and with the screw attached is brought to the site by barge or otherwise, the capstan head is then fixed, and the pile swung vertically over the pitch by sling-chains fastened to temporary eye-bolts passing through the bolt-holes in the flanges or otherwise, and is moved either by a jib crane, a derrick upon a raft, or some such hoisting apparatus; it is lowered into its place between the guide-piles or steadied by sling-chains or other means, then the capstan bars are put into the sockets of the capstan head, which should be at equal distances apart, and the pile is ready for screwing after it is known that it is vertical.

"Where circumstances did not allow of room for capstan bars of sufficient length for men to walk round, I have screwed piles by ropes, but it will only do when the soil is easy to penetrate. The way we worked was something like this, we had two endless ropes passing round the ends of short capstan bars and round two double purchase crabs placed upon opposite sides of the pile, about six or eight men worked at each crab, four or five winding, and two or three hauling in the slack, one rope being passed through a sufficiently deep upper slot in the capstan bar end so that it did not slip, also one in the lower slot same end. Both the taut and the slack ends of the lower and upper ropes were attached each to its own crab. A man must be stationed at the end of the capstan bars to put the slack ends of the taut and slack ropes into the slots. One rope gives the capstan half a turn when it is taut, and then it falls out of its slot and is slack, and so with the other rope, but it is not easy to keep the two ends of the rope equally tight, and the power obtained is not great and may not be sufficient. It is a kind of makeshift."