RAILROAD FALSEWORK GRADE 8. This grade includes red and all other oaks not included in Railroad heart grade, sycamore, sweet, black and tupelo gum, maple, clot, hickory, Norm-ay pine, or any sound timber that will stand driving.
0. The requirements for size of tip and butt, taper and lateral curvature are the same as for Railroad heart grade.
10. Unless otherwise specified piles need not be peeled.
11. No limits are specified as to the diameter or proportion of heart.
12. Piles which meet the requirements of Railroad heart grade except the pro portion of heart specified will be classed as Railroad Falsework grade.
Piles are driven with the tips clown, although in some instances it is desirable to drive the butts clown. In certain soils, as quicksand, the upward pressure on the sides of the piles may force the pile ward after being driven with the tip down. Where piles are being driven through soft material to a hard substratum, it may be desir able to chive them with the butts down in order to obtain larger bear ing surface at the base.
The butt of the pile is cut off accurately at a' right angle to its length in order that the blow of the hammer may be uniformly tributed over the section. When the strikes directly upon the head of the pile, it is common to use a hammer with a slightly concave upper surface. This tends to keep the pile centered in the leads, and minimizes the hroonring effect of the blow. Heavy blows upon the head of a pile have a tendency to splinter and broom it, and a portion of the energy of the blow is used up in injury to the pile. When the brooming effect has become considerable, the efficiency of the driving is greatly decreased, and a large portion of the work is wasted. It has frequently been observed that when the broomed head of a pile has been cut off, an increase in the penetration under each blow is obtained, the penetration being in some cases more than doubled.
Pile rings are frequently placed upon the heads of piles to reduce the browning, effects. They are made of wrought iron from 2 to 4
inches wide and to 1 inch thick; the pile is chamfered off so that the ring may he started on and be driven into place by the hammer. The rings are used repeatedly and serve for a larger number of piles. Pile caps consisting of cast-iron blocks with tapered recesses above and below are used for the same purpose. The head of the pile is fitted into the lower recess and a hard-wood block into the upper one.
The block is reinforced by a ring at the top and receives the blow of the hammer. The cap fits into the guides of the leads, and holds the head of the pile in place. After the pile is in place, the cap is drawn from its head by being attached to the hammer. Some steam hammers are provided with anvils, which rest upon the head of the pile and receive the blow of the hammer.
In driving piles through hard material, it is often desirable to point the lower end, by cutting the end of the pile in the form of a pyramid, a blunt end 3 or 4 inches square being left at the bottom. A thinner point is apt to be too easily injured.
When piles are needed of greater length than those available, it becomes necessary to splice two piles together, which is accomplished by the use of fish plates. The ends of the two piles are cut square and butted together, the sides are trimmed flat for a considerable distance on each side of the splice and long wooden fish-plates are spiked to the sides, four or six fish-plates being commonly used.
194. Bearing Power of are so many variable factors affecting the supporting power of pile foundations that in most in stances accurate determinations are not possible. Piles may derive their support either from a hard stratum at the bottom which resists the penetration of the foot of the pile, or from friction of the sides of the pile upon the material through which it is driven. Conditions may also vary widely as to the lateral support afforded the pile be tween the loaded end and the point of support.