As the several types of concrete piles have been devised through the need of meeting differing conditions, each has advantages for certain kinds of service and is unsuited to certain other conditions. Careful determination of conditions must always precede choice of method of construction.
196. Sheet Piling.—Sheet piles are made to fit closely together and are driven in contact with each other so as to form a wall to pre vent the Literal flow of soft materials, anti find their greatest use in enclosing areas which are to he excavated, or guarding foundations against undermining by currents of They nlc wade of timber, steel, or concrete.
The simplest and most common form of sheet pile consists of a thick plank sharpened (as shown in Fig. 115) to a point at one side as so to cause each pile to drive closely against the one previously driven. When heavy timbers are employed, they are sometimes arranged with tongue and groove, which may be planed into the edges of the planks, or made by nailing strips to the edges. In some instances these are made to dovetail together.
Wakefield sheet piling is formed by bolting and spiking three planks together so as to form a tongue on one edge and a groove on the other, as shown in Fig. 116. The patent upon this pile has expired. They have been quite extensively used in this country and for heavy work are preferred to the other forms of wooden piles. They are made of planks from 11 to 4 inches in thickness, depending upon the strength needed in the work, and are bolted together by pairs of 1-inch or f-inch bolts, 6 or 8 feet apart, and spiked between the bolts. The planks are 12 inches wide and the tongue is made as wide as the thick ness of plank, but not less than about 23-, inches for the thin planks.
Steel Sheet-piling is made in a number of forms either built up from standard rolled sections, or rolled in special sections so that the piles may interlock. A few of these forms are shown in Fig. 117. In form A, known as the Jackson pile, two channels bolted together with pipe separators are used alternately with I-beams. The Frie
stadt piling, B, consists of alternate channel bars interlocking with channels having Z-bars riveted to them. Form C is made up of I-beams held together by a special locking bar. Forms D and E are special rolled sections, the ends of which are designed to interlock, and may be used in work curved in plan.
For temporary work, where the piling is to be removed, steel sheet piling is largely used and is often more economical than timber pil ing. The interlocking edges hold the piles together in driving, and give a certain amount of transverse strength to the wall. In hard driving, the steel piing is less injured than timber piling and it may be repeatedly used.
Reinforced concrete sheet-piles, shaped like wooden piles, either rectangular or with tongue and groove on the edges, are often used on important work where the piling is to be left permanently in the structure, and are often reinforced with longitudinal bars to resist the stresses occurring in handling and driving. The loads coming upon them after driving are in a transverse direction and the piles should be designed for hydrostatic pressure, being supported laterally by the waling.
Concrete sheet-piling is sometimes made interlocking by setting interlocking steel bars in the pile edges, the interlocking parts being then enclosed in concrete after driving. In some instances semi circular grooves are left in the edges of the pile, the circular opening between the piles being filled with concrete after driving.
In driving sheet-piling it is necessary to first drive a row of guide piles to which may be attached horizontal timbers, or wales, against which the sheet piling may be driven. The driving of ordinary sheet piles is much lighter work than driving bearing piles, and light steam hammers are used for the purpose. These are frequently operated from a derrick wit hunt leads and may be ham fled with greater rapidity and less injury to the piles than the ordinary heavy driver.