"Yes, they are all right for fine sand and silt, but you must be careful the discs are the same in form and dimensions upon all sides, or a pile will almost certainly tilt and sink crookedly. I was busy on the Lancashire coast once, and heard that Mr., now Sir James Brunlees, tried a lot of different kinds of hollow disc piles, and that the best was one with a plain f.l.a.n.g.e base three times the diameter of the pile, and circular, with the bottom nearly closed, it only having a hole in it in the centre of the base 3 inches in diameter. Some ribs and cutters were cast on the bottom of the disc to break the ground up if it was hard. This is what I know about disc piles and have been put up to.
"When piles have to be sunk by water pressure, rotate the pile, and don"t let it be still long, so as to lessen or prevent surface friction on the pile shaft and the sand settling round it. Always have circular discs and not too large, not above 3 feet in diameter, for they do not sink nearly so easily as the size of the disc is increased. About 2 feet discs are my choice as they go down much quicker than 2 feet 6 inches or 3 feet.
"Don"t try to sink them in sand to a greater depth than 18 to 20 feet, and remember that although they may sink easily for about 12 or 15 feet, afterwards they will want some labour. When you have finished sinking piles with the water-jet, it is best to drive them down an inch or two further by a heavy ram and a very small fall, or heavily weight them as soon as possible after having done with the jet; then the disc has a bearing on firm and undisturbed ground, and if you are afraid of a blow on the pile you can have a heavy weight placed on it to help it into position and the sand to become solid. Obtain considerable pressure of water, and always cause the pile to rotate when sinking.
Don"t let the pressure get much below 40 lbs. per square inch, and use about 60 lbs. if you can get it. I have worked up to 100 lbs. per square inch but not beyond, and fancy there is then too much pressure, and that more sand is disturbed than is necessary. All that is wanted is to make the sand boil and remove itself from the underside of the pile and disc, but always have a few ribs or cutters on the underside of the disc as they loosen the sand as the pile is rotated--besides, should there be a strip of harder soil, it may be impossible to sink the pile without them. A rather large tube and a moderate pressure are best, and a tube not less than about 2 to 4 inches in diameter according to the size of the pile, and it is better from 3 to 6 inches, of course, if the pressure is high a larger size jet can be used, but if it is less than 2 inches it will only make a small hole, and too much below the disc, and not enough water pa.s.ses through it. Try to ascertain what pressure of water makes the piles sink the easiest.
Sometimes they will go down at the start as much as 3 feet in a minute, and often 2 feet, and from that to 1 foot they should do for about the first 6 or 8 feet in sand, but then the rate quickly decreases. The nozzle should be properly shaped so that the jet is whole. I mean the shape of the pipe at the place where it touches the sand. What is wanted is to get just enough force to cause the sand to separate and boil and to push it away from the disc and no further, or some of the water power is wasted, therefore a good volume of water is as necessary as a high pressure. You understand?"
"Yes."
"The tube should project about 6 inches below the bottom of the disc. A toothed tube can be fixed round it so as to help to disturb the ground and strengthen the pipe. The water supply may perhaps be obtained at a sufficient pressure from the local water-works company, then, probably, a force pump will not be required, but the pressure that can always be relied upon should be known.
"In sand, and when the water power can be easily obtained, I prefer disc piles to screw piles, because there is hardly any chance of breaking or injuring the disc; you always know where the disc is, but cannot positively say where the screw is--it may be sound and may not be; in addition, the disc is stronger than a screw blade, as it can be strengthened by ribs almost as much as one likes, and the disc in sinking is hardly strained at all compared with a screw pile. They can be sunk quicker, and do not require nearly as much plant to do it, for when you have a force pump, a guide frame--something like an ordinary pile-driving machine 25 or 30 feet in height, with a grooved pulley at top in which the chain or rope runs so that one end can be attached to the pile f.l.a.n.g.e either by jaws or temporary bolts, and the other to a crab winch, which, with the guide frame, is used for lowering and keeping the pile in position, and stay the top of the guide frame by ropes to short piles driven into the ground--and a hose and two levers, with a collar to grasp the pile so as to rotate it, you have about all the _special_ plant that is wanted.
"Of course, piles can be sunk by water pressure from a floating stage such as a barge, pontoon, or raft, so long as the pile is kept vertical, but there are the same objections to that method as with other piles. Piles are, however, got down much quicker and easier by the water jet than by s.c.r.e.w.i.n.g or driving, but the ground must be loose granular soil, such as ordinary sand.
"There is not much "extra" to be got out of iron piles. You can only dodge a bit with a length short now and then when you have the right parties to work with, and the inspector is cross-eyed or a star-gazer, but you may get something "extra" out of the filling them in. As usual I draw the line somewhere. Everything on earth has a boundary line.
This is where I draw it. Listen!
"After as much water as possible--possible is a nice elastic word--is got out of the pile, and it is as clear of deposit as convenient--another nice easy word--and before commencing the filling, I put inside the pile everything I can get hold of that is dry, for just then I have but one way of looking at anything, and that is to consider it Portland cement concrete, unless it costs me more to use it; but when the filling is concrete, I make that as dry as mixing will allow, and sometimes hardly that. The inside of the pile is sure to be wet, and that will help the mixing. I never ram the concrete, but gently cast it in. It is only a sort of anti-rust covering, and is put in for that and to keep water out, and no weight comes upon it--it is not like the hearting of cylinder bridge piers. Ramming the concrete is not far from being a mistake, because the pile should have a chance of contracting without straining, and may be it will crack; and it is just as well to remember that although by ramming tightly you may get more solid filling and better protect the inside from rust, the pile may be strained, and it is a choice of evils, possible rust, or strain."
CHAPTER V.
TIMBER PILES. PILE-DRIVING.
General Consideration.
"Now, as promised, I will tell you of a little bit of free trade with some timber pilework."
"That"s it. I am waiting for it."
"Well, they let me have 400 feet run of pile-driving. Double row of 16 to 12 inch piles, and there were some fine sticks nearly 55 feet long, and that is a long length for a sound pile, and you have to pay for them."
"Before you begin to tell me how you scamped it, give me a hint or two about piling, and say what you have learned from experience."
"All right. First, when a pile is some distance below the bottom waling, which should be fixed as low as possible, a lot must be taken for granted, and it cannot be controlled much. I know this from drawing many piles; hundreds, I may say. After they are down about 5 or 6 feet they begin to do as they like, and take to irregular habits, and you cannot be certain the points are straight unless the ground is the same throughout, and it hardly ever is. In fact, the resistance they meet with varies, and then they accommodate themselves to circ.u.mstances; and even when the ground is very soft they turn to the line of least resistance, and if they have to be driven through several feet of soft earth to reach the solid, they may play tricks and bend about in the soft soil in go-as-you-please style, yet seem to be driving nicely; or they may stick between boulders and can"t be driven further and appear to be firm as a rock, and so they may be as long as the boulders do not move, but they often do after a time, should the ground become wet, and sometimes when the next pile is being driven.
"Always be careful to see that the shoe has as large a bearing as possible for the end of the pile, and is long in the point, and more pointed as the soil is harder. Take a 12-inch pile with a 4-inch or so seat in the shoe for the stick. Well, 12 by 12 is 144, and 4 by 4 is 16, and therefore the pile end has a bearing area upon the pile shoe of one-ninth of the area of the pile. No wonder the bottom often becomes ragged and the pile shifts. The shoe should have a good hold of the timber, and be put on true to a hair, so that the point is in the exact centre line of the pile, or look out for squalls. Now high falls and light monkeys are out of fashion, and short falls and heavy monkeys are the thing, not so many piles are injured. Pushing them down is better than breaking them to bits. You should have the monkey so that its centre falls upon the centre line of the pile. The average centre of the pile should be marked on as exact as possible, and the end of the pile be cut to a template, so as to make it fit tightly to the shoe, or it may not drive straightly. I always take a lot of trouble that way and seldom have to draw a ragged one, and believe they used to drive straight. I mean from start to finish about the same number of blows and to the same depth and vertically.
"When hand-driving in soft earth--it"s slow business at the best--weight the pile when the monkey is being lifted so as to stop the quivering and press it down and keep it from springing. Provided the work was of importance, and I was the Caesar of it, before any pile was pitched ready for driving it should be inspected, its dimensions taken, it should be numbered, numbers be burnt in, and every foot from top to bottom should be marked on by a brand; and perhaps the numbers should begin at the bottom and work up, as there is not so much chance to tamper with two figures as with one, &c.
"Pile-driving is fickle work, for sometimes the piles stick because the points can"t pierce the earth, and at others because they are held by friction on the surface of the piles. I have known the shoe to be cast, and the pile end look like a ba.s.s broom, and to be all in shreds. When piles split a great deal and they must be driven, the best thing to do is to get harder wood, lessen the fall and increase the weight of the monkey; same as in tunnel lining, when stock bricks are crushed, blue bricks have to be put in. The nature of the ground should govern the hardness of the wood for piles. I always pick out darkish even-coloured wood, and sniff for the resin, and the more in it the better for me.
You don"t catch me driving many white wood piles, for they become dry and break off short, and are not the timber for piles. Once a bother arose about some piles. There was a layer of hard gravel, and by the way the piles were driving I knew they would split, so I gave the word that Memel piles were not hard enough for such gravel; and I worked it humble like, and said to the engineer, "I think you will agree, sir, you can"t expect me to be answerable for smashing them until we get into the soft ground again. It wants rock elm or as strong timber for this soil." After smashing a few to shreds, they supplied us with rock elm piles, and then we managed. It is true to say in the same soil the harder the pile the better it will drive, and therefore with less trouble and expense. The monkey should have an even widened-out base where it touches the pile head, so as to get the weight as near the head of the pile as possible; it also falls straighter than the long thin rams of nearly the same width throughout. Grease the ways well, and take care they are as straight as a die, and exactly vertical if it is upright pile-driving, and you"ll save money. Make the blows quickly in fine-grained soil, so that it has not time to settle round the pile.
In clay there is no occasion for such quick-driving, but take care to prevent the piles rebounding. Remember the same system does not do for every soil, for quick driving in hard soil sometimes smashes the piles; perhaps the earth has not had time to become displaced nicely and settle before being jammed again, and then the pile point turns and quivers and soon shreds, and cannot be driven down properly. Anyone that says piles make the ground itself firmer when they are driven into it, and so cause it to support a heavier load, will have to prove it before that can be swallowed. It is the friction on the sides of the piles that princ.i.p.ally sustains them and not the bearing of the points.
In hard soils drive slowly, for it is like chipping up a stone with a hammer. You must do it gently, or it will break the tool; and as you can"t clear out the hole in driving piles, it seems to me time is required instead, so that the pressed out soil may settle away and take a bearing. I tricked a chap once pile-driving from a barge."
"How did you do it?"
"Well, it was bound to be driving from a barge or nothing, and there were three pile-drivers for us, almost as many as we could work, as the driving had to be done by degrees. Some of the work was let to a chap I did not like too much, and the rest to me. They gave me the choice of plant, so I said to the engineer, "May I have two of the pile-drivers upon my barge, as f.a.ggitts"--that was the other chap"s name--"only wants one." I got the two. Now f.a.ggitts knew about driving piles on land, but had never done any driving from a barge, so I had a bit in hand of him. If you take any pile-driving and it has to be done from a barge, have more than one pile-driver on it if you have the chance; but don"t place them close together, make one steady the other, and have as many as you can conveniently work at once; because, in my experience, the more you have the less the swaying, and the piles drive more regularly and the barge is steadier, and you don"t have so much bother with the moorings. Of course, if the monkey does not fall flat upon the pile head the pile does not receive the full force of the blow in the right direction, the pile may be driven slightly crooked and it does not get properly treated and won"t penetrate so easily, and therefore you lose money. Old f.a.ggitts found that out in the soft soil we were driving them into. I said nothing to him, but he did to me. I never told him.
"I have read somewhere that it is wearying work going into details, but when you have to do the work yourself, unless you take care of the details you"ll find they will make it hot for you; and after all, any one can speak generally, but when they have to explain in detail what they think they mean, and have to do the work themselves, they will soon find out that unless you know the details and attend to them carefully, that you won"t make a profit nor anyone else. Anybody can talk tallish after about a fortnight"s training, but then they have to pull up or they will fall at the next fence, which I label "details wanted." That"s by the way, and I may have made it too strong, but it is as well to sound your engineer. No general is successful unless he knows the strength of his enemy and as much more about him as he can, and acts accordingly, and chooses his own time and place for a battle.
"Driving piles in groups, especially if the ground is soft, and not singly, is good. They go down more regularly and fit tighter, and they seem to drive quicker. I have driven cheap fir piles between elm piles that way, and a good many of the soft ones split when we had to drive them singly. Have as few key piles as possible, because they are liable to be jammed before they are down to the right depth, and then, if it is a cofferdam, it is probable a leak will occur under the key pile, because it is the easiest place for the water to soak through, and the other piles being down below it, stop the flow, and it soon finds out the short-driven key pile. When I notice a spot in a cofferdam at which water leaks through the bottom, unless it is an old stream bed, it occurs to me that the piles have not gone down properly, have got bruised, bent, turned up, or broken off, and I have found out that was the case on drawing them when the cofferdam was of no further use. Once I was ordered to drive some three-cornered piles at the turns in a cofferdam on a river front, but said, "Square or circular shall be driven, but any other shape I will try to get down properly, provided they are carefully fitted and bevelled, but you really can"t expect me to be answerable." They deducted a fixed amount if after the piles were pitched there were more than a certain number visibly damaged or smashed, so you may depend I had a good look at the sticks before they were driven.
"I have driven piles 60 feet in length, kind of giant sticks, but 45 to 50 feet is long enough for good sound piles. Socket pile driving piecework I avoid, for the joints are ticklish business; and if a pile of ordinary length will not do, I throw out a mild hint whether the better system to use would not be Indian brick or concrete wells, or to spread out the foundations so as to get a sufficiently large bearing, or have a fascine platform, and sink it till it is firm, and test its stability properly by a load.
"There is a great deal in starting the driving correctly. I always am very careful at the start, and experiment and watch how the piles drive, and vary the fall a little until the best is known. Few considerable stretches of ground are of the same kind, and to fix a certain fall throughout is not the thing, it generally wants varying. I have easily driven piles in fine sand by having two small pipes, one each back and front, reaching a few inches below the point of the pile, and sending water down them under pressure, and by keeping the pipes on the move so that they can"t be gripped. I worked out with the pipes the place where the pile had to be pitched and made a profit that way, because not only did the piles go down much quicker, and a lot of blows were therefore saved, but the piles were easier to start right. I used to call my two pipes the two bobbies, because they steered straight for their station, and these two did the same office for the piles.
"Now a word as to systems of driving; the method must suit the ground.
I knew a man that believed in nothing but driving by gunpowder; he must have been going in strong for gunpowder tea, or have been in the militia, for the soil he had to do with was not h.o.m.ogeneous, and had boulders and other hard obstructions in it. It was not like soft sand and clay, consequently many of the piles were broken. The noise also was a nuisance in the dock, and cattle that had to be unshipped from the steamers were so unruly that they had to stop the gunpowder pile-drivers; besides, to do much good with them, a large charge is required, or it costs too much. The power necessary to work the machines is better obtained by other means, and can be without so much noise or shock.
"I have used all sorts and sizes of monkeys, from half a hundredweight to four tons, but heavy rams and short falls are the best, and steam for the power if the contract is considerable and will pay for such plant; otherwise hand, unless the piles are large and have to be driven a long way. A sixteen hundredweight monkey is about heavy enough to work nicely by hand, but it is not sufficiently heavy for a 12-inch pile, except in soft ground. For sheet piles a hand machine is good enough, for it can be moved easily, and six to eight tons weight, being about that of a steam pile-driver, costs something to shift, unless there are rails and tackle handy. Of course the blows are quicker with a steam pile-driver, and in sand that is a great point as the ground has no time to settle round a pile; but should the soil vary and be hard and soft, it is well to slow down the machine at first to lessen the fear of smashing the piles and shaking them till they tremble to destruction. I have worked a lot of different kinds of plant, and driven many piles at once, and the power was obtained from one engine giving the motion by driving bands, and in another case with drums fixed on the engine shafts, the chains being carried over sheaves to the different pile engines.
"This is my idea of pile-driving:--
"1. Steam driving. 2. Hand driving, if the piles must be driven very slowly, and there are not many to drive. 3. Never use gunpowder pile-drivers, always prefer steam, hydraulic, atmospheric, or some other motive power.
"Gunpowder is more for blowing up than anything else, in my opinion, and I know the pile shoes often shed in driving with it; that is, they loose their hold of the piles and become detached.
"A pile should penetrate regularly, and after the first few blows drive less and less, as then you have a good idea it is all right and uninjured. Uneven penetration is a proof that piles are not all right, and when they sink suddenly there is almost sure to be something wrong, and they are most likely being over-driven, shredded, frayed, shoe-cast, or split up. The rate of descent should be noted. It may be considered they are driving properly if they sink about a foot at a blow for the first one or more, and then 8 or 6 inches, and when they get down to one-eighth, one-fourth, or half-an-inch a blow for some successive blows it is time to stop and consider. I have driven piles with as few as ten blows in sand with the aid of two water pipes at work fore and aft, as mentioned before, and have had to give a pile as many as 300 blows, and when they want as many as that, with all due deference to everyone, the ground is firm enough to build upon for permanent foundations without piles. My experience goes to show that piles are often driven further than they need be, if only for use as a cofferdam, and that back struts and counterforts are better than extra depth in the ground, provided leakage is prevented. 8 to 10 feet down for solid clay, 10 to 12 feet in gravel, and about 15 feet for ordinary soils, and more care taken to ascertain the piles are where they should be, and that they are sound and whole, and not turned aside, bulged, and injured, would be my practice. In boulder ground, in my opinion, piles should not be adopted; for broken, crushed, and twisted fibre ba.s.s-broom shreds are not piles; they are out of place and should be used for clearing leaves from garden walks. The longer the piles the softer should be the ground they have to be driven into, or they shake so much, and cost more to drive.
"Unless always well buried and at such a depth that neither the moistness nor condition of the earth vary, I scarcely believe in timber pile foundations at all, except in very peculiar cases, and as a kind of aid to the main support or to help to prevent the toe of a wall from being thrust forward, but for cofferdams, jetties, piers, and such structures, of course they are useful. In hard and most gravelly soil avoid them, and also in sharp sand, if you cannot use the previously-mentioned water-pipe arrangement fore and aft; and although in ordinary clays they drive nicely, and you make a bigger profit than in sand, it puzzles me to discern what is the use of them for permanent foundations, except to help to prevent a wall sliding forward, because when a pile is driven into most clays the clay becomes tempered and softer, and a layer of concrete put in a proper distance down is better and much more certain, and distributes the load more equally. Elastic soil is bad in which to drive piles, for it yields and then rebounds. A pile will sometimes spring back almost as much as it is driven, and in such a case it is well to let the ram or monkey rest on the pile immediately after the blow is given, if you are hand-driving, or have an arrangement so that it is weighted directly each blow is delivered, and perhaps the best way is to hang heavy weights on the pile. In driving in firm sand the ground at the surface becomes considerably displaced, in clay about half as much as in sand.
"Pile-driving is different to masonry, and I always read the specification for pile work, and then judge whether and how a bit "extra" is to be obtained, and guess as to the knowledge of those I have to deal with, and act accordingly. Sometimes a specification simply says all the piles are to be driven to the same depth or as shown on the drawings. That may be right should the ground have been tested by experimental driving, or the nature of it be known; but if not, I don"t take much notice of the specification, because I hate waste, and can"t afford the luxury; and it stands to reason that simply because a lot of piles are driven to the same depth they are not equally firm, nor will they support the same load unless the soil is exactly the same, and they drive well and regularly to the same depth and all nearly alike inches by inches, and this seldom occurs. Often "extra" profit is to be had, as you will soon hear described, for when piles will not drive further than half or a quarter of an inch a blow they satisfy me they are tight enough for the purpose intended if they are at a fair depth and not wedged by boulders; but between ourselves, should a building of any kind have to be erected on piles, and anyone I really cared about had to live in it, I should always weight the piles for as long a time as possible after finishing the driving and reasonably more than the permanent load, watch the effects, and act accordingly, particularly in elastic soil.
"Remember a pile sinks less after it has rested than if it be driven continuously, therefore always take note of the set when the driving is proceeding, and not just at the start, or after an interval, although one does that for one"s own benefit, and with a view to "extras"; and no one wants to drive a pile an inch more than can be helped--at least I don"t, nor have I, and it is certain never shall.
"You want to know when to stop driving. The time has arrived when a pile penetrates very little, and nearly equal for several successive blows of the heaviest ram by which it has been driven at the usual fall.
"A word as to tie and sheet piles before referring to the way I have worked piles for "extra" profit. It is difficult to make a main pile and a tie act together, one or the other is nearly sure to have to bear more than its proper strain, and the tie rod becomes eaten by rust, bent, and loose in the piles. In taking down old banks and quays you will generally find the main pile and the tie pile are not held tightly by the tie rod, the tie pile is loose or pulled over, perhaps when first strained, and then becomes disengaged when the main pile has set to the strain. The tie rods want to be very carefully and frequently adjusted, if possible, and big washers and cleats on them are required.
They hold best in firm sand, not so well in clay, and in large light loose soil, such as ashes, they are not much good. It is an impotent arrangement and it is always uncertain whether they will act together.
Don"t undertake to tighten up the rods. Fix the piles, and let the engineer see to the tightening up, as you may injure the piles.
"When I have to drive a lot of sheet piles, of course the piles are supplied to me, and I only take the driving. You may be sure the timber is right, and that the edges are sawn square so as to drive tightly together, and that the point is in order. I find it always pays well to temporarily place a baulk at the ground line like a waling, but not fixed to the sheet piling, as it guides the piles, lessens the shaking, and they drive easier and better. It appears to me piles cannot vibrate without force, and that is not where it is wanted, so it is wasted motion. Agitation when drawing piles is all right, but when you are driving you want it in the ground itself, and not in the piles. Once when I had to drive some thin sheet piles, I made a movable guide frame, the side against the sheet piling being planed and greased. It was like one bay of a timber-lattice bridge, and it well paid for itself as it steadied the piles.
"In taking a contract for drawing piles always find out how long the piles have been driven, for if they have been down many years they will be much harder to draw than if they have only been fixed a few months.
They can be drawn by lever, hydraulic jack, and chains, and pontoons in a tide way."
CHAPTER VI.
TIMBER PILES.
Manipulation for "Extra" Profit.