Form a, Fir. 86, may be made of any size of channels and I-beams, although the 12-inch or the 15-inch are ordinarily used. With this form of pile, the space between the channels can be tamped full of clay and thus make the wall water-tight. Form b is made with two weights of 12-inch and also with two weights of 15-inch channels. There is another variety of this form in which there is an angle on each edge of the intermediate channel to form a calking joint, but such a joint is seldom necessary. Form d is made of a 12-inch I-beam and a 5-inch locking piece or a 15-inch I-beam and a 7-inch locking piece. Form e is made in three sizes-12-inch 40-pound, 12-inch 35-pound, and 6-inch 11-pound. With this form of pile a half-round wooden strip may be driven in the joint, which upon absorbing water expands and prevents leakage. It has been proposed to run grout into the interlock of sheet piles to prevent or stop leaks.
A great variety of forms of steel sheet piles has been proposed, the catalogue of one manufacturer showing twenty-seven different forms exclusive of special corner pieces; but the above are the forms in most common use, and are fairly representative.
By the use of special corner pieces, a right-angled corner can be turned with any of the steel sheet piling; and some of the regular forms can be used to inclose a comparatively small circular area. Steel sheet piles are ordinarily driven by allowing the pile hammer to strike directly against the end of the pile; but in hard driving a cast-iron or steel hood, into the under side of which fits the top end of the pile, is sometimes used. These hoods are furnished by the makers
of the piles.
Steel sheet piles are superior to wooden ones in that they make tighter work, are easier to drive, may be used repeatedly, and some forms have nearly their original value as standard sections when no longer required as piles, and all forms have value as scrap when they can no longer be used as piles. Steel sheet piles are more easily pulled out than wooden ones, since a hook can readily be inserted in a hole near the top. Steel sheet piles require less bracing across the coffer-dam than wooden ones. Steel sheet piles may be spliced by driving one section on top of another; and, by varying the length of the members, a stout wall of almost any depth may be built. Most forms of steel sheet pile speedily become water-tight in muddy water; and usually all are easily made tight in clear water by throwing sawdust, paper pulp, manure, etc., near a leak.
In selecting a type form of steel sheet pile, attention should be given to the clearance between the members and also to the lateral stiffness of the pile. To secure tightness the clearance should be as small as possible, but too little clearance makes trouble in driving, owing to kinks and bends in the members. Lateral stiffness is important in hard driving; and depends upon the cross section of the pile.
Some forms of steel piling are provided with cast-iron points to facilitate driving in hard or stony ground; but usually the pile is driven without sharpening or without a shoe.