This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
71. We now come to the subject of piling - an important branch of foundation work, which, though not masonry work in itself, is, as a supporting- structure, yet considered as pertaining to masonry construction.
72. A pile may be considered as a column with a base more or less rigid, according to the nature of the soil into which it is driven. If a stick is driven down into damp sand, it will stand upright and support a load, even though it may not have reached firm bottom, the friction of the sand - or the pressure of its particles against the sides of the stick or pile - holding it in place. Thus when a pile is driven into the ground and its lower end rests on stiff clay or gravel, it is held in position by the friction against its sides.
It is usual to excavate to a point below where the heads of the piles are to be cut off, in order that they may be leveled up before the concrete is put in or the foundation begun.
73. Piles are usually driven by successive blows of a heavy block of wood or iron, falling from a height. This block weighs from 1,200 to 2,000 pounds, and is called a hammert monkey, or ram. It is raised by means of a rope or chain that passes over a pulley fixed on top of an upright frame, and falls between parallel guides directly upon the head of the pile that is placed under it. The chain or rope is wound over a drum, which is driven by a small engine. After the hammer or ram is drawn up to the required height on the frame, it is released, and falls on the head of the pile, forcing it into the ground.
When the weight of the hammer and the height from which it falls are known, the distance a pile sinks at the last blow determines somewhat the load it will carry. The pile should be driven until it sinks not more than from 1/4 inch to 1 inch at the last blow of the hammer, depending upon the character of the material into which it is driven.
74. Piles are generally round, and from 9 to 18 inches in diameter at the head, and should be straight, and clear from bark and projecting limbs; but where piles are exposed to the rise and fall of tides, it is considered best to drive them with the bark on, since they are then not so easily-affected by the action of sea-water, and are not likely to be attacked by the teredo navalis and other boring sea worms. Oak, spruce, hard pine, cypress, and elm are the principal woods used for piling. Oak has the advantage of being hard and tough, and stands hammering well, but cannot be obtained in as large, straight, or long pieces as spruce, hard pine, or cypress. The long-leaf pine is hard and tough and can readily be obtained in good-sized logs of lengths up to 90 or 100 feet, and from 12 to 18 inches diameter at the butt, and from 5 to 12 inches thick at the lower end.
75. Piles are prepared for driving by cutting or sawing the large end square, bringing the small end to a blunt point with an ax, the length of bevel being from 11 /2 to 2 feet.
In very soft and silty material, there is no necessity of pointing the pile, and in fact it can be driven in better line if left blunt. A pointed pile on striking a root, or any obstruction of the kind, will invariably glance off and thus be thrown out of line; the blunt pile, on the contrary, will cut or break through the obstruction.
The large end of the pile should be cut or chamfered for a few inches from the end, so that a wrought-iron ring, 1 inch in thickness and 3 inches wide, will fit over the end of the pile tightly when struck one or two light taps by the hammer or ram. Sometimes a ring from 1 to 1 1/2 inches less diameter than the pile is simply placed on the top of the pile, and driven into it by light blows. This, however, is not as desirable as the former method, as the ring is apt to split long pieces from the sides of the piles, and not usually being put on until the pile is more or less battered on the end, is likely to be carelessly placed, and not concentric with the head of the pile. The rings are used in pile driving in order to lessen the tendency of the pile to split or broom. Brooming is a term given to the splintering of the fibers on the end of the piles, due to the repeated blows of the ram.