"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 homogeneous, 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 bass-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.