Steel sheet piling is made by a number of manufacturers, each making special claims for their own product, such as interlocking features, general shape of the cross secton, and ability to form offsets and turn corners.

This type (center flange) is designed for construction requiring high tensile and compressive strength in the pile section, together with a fairly high transverse strength. The center flange, as rolled on this section, acts as a stiffener to the web, increases the modulus of the section, and furnishes a means for attaching transverse ties, braces, etc., needed in special work, and tie rods used in binding on protective concrete facing in permanent protected construction.1

7. Pile Driving and Pile Pulling Equipment.

7a. Pile Drivers.-A pile driver (Fig. 18) is used in driving either timber or concrete piles and consists of two main parts-the bed and the leads.

The bed is mounted on rollers and supports the operating machinery. Pile drivers are mostly steam operated as the steam hammer is commonly used in driving. The operating machinery consists of a vertical boiler, engine, and two drum hoist-one for the pile line, the other for the hammer line. The bed is composed of timber sills long enough to allow the boiler, etc., to be set back from the leads to provide proper balance.

1 From Lackawanra Catalogue.

The leads are long vertical members, rigidly connected to the sills opposite to the boiler and framed with back stays to form a tower. The leads carry at this upper end, sheaves for the hammer and pile lines; and along the sides, guides for the hammer. The leads in the smaller drivers are composed of wood, suitably cross braced, with the front open to allow for placing the pile and operation of the hammer (Fig. 19). In the. larger sizes the leads are made up of structural steel. The leads must be of sufficient length and strength to hoist a pile from a position on the ground to starting position in the leads.

In driving precast concrete piles, the pile driver and its equipment is called on to withstand greater stresses than is the case when timber piles are used. Precast piles of 30-ft. length, average 2 to 4 tons, and larger piles about 6 to 8 tons in weight.

Locomotive cranes can be made to serve as pile drivers and in a number of instances have given very satisfactory service. In such rigs, leads are suspended from the boom and rigidly connected to the base.

In driving piles below the reach of the leads, two methods are employed. One employs a "follower,"

FIG. 19.-Steam hammer showing detail of hinged leads, ram, and driving cushion, Raymond Concrete Pile Co.

which is a stick of timber with some socketing means of holding the two in proper alignment. The other method utilizes telescopic leads fitted inside of the stationary leads and handled by a third drum. This latter method is not used except where a number of piles are to be driven below the sills, as at the bottom of trenches or in cofferdams containing a large amount of cross bracing.

The total weight of a pile driver will depend on the size of pile to be driven and the weight of hammer used. These in turn will determine the dimensions and weights of sills, leads, and engine. An approximate weight of a driver using 50-ft. wood leads with a 4000-lb. hammer which will require an 84 X 10-in. engine weighing 12,000 lb.. will be a total of 15 to 18 tons.

Where jetting is to be carried on in conjunction with pile driving, the engine is equipped with a third drum or niggerhead to carry the lines supporting the jet pipe or pipes.

76. Pile Hammers.-Hammers used with the pile driver and for driving sheet piling are designated, according to the manner of their operation, as drop hammers or steam hammers.

Drop Hammers.-Drop hammers (Fig. 20) are so called because they consist of a weight hoisted to some distance and allowed to fall. At the top is a ring to attach the line and at the sides are grooves to fit the guides of the pile-driver leads. Drop hammers are made relatively long to insure bearing in the guides and to prevent jar when the blow is struck, but a small amount of play is allowed in the jaws. The bottom is made slightly concave if it is to strike the head of the pile direct, but when a cap is used, the bottom is made flat. The center of gravity is as low as possible.

The hoisting and release of drop hammers is controlled in two ways. One is by means of a friction clutch on the drum, the hammer being hoisted to a desired height, when the clutch is released. The blow is therefore equal to the hammer weight falling through this distance, less the friction of the guides, and the pull to unwind the line from the drum. The other method is to attach the line to a block which contains fingers or triggers which automatically release the hammer at a desired height. Here the full force of weight and distance, less friction of guides only, is utilized in driving.

With the first arrangement, either light or heavy blows may be obtained and no time is lost in reconnecting line and hammer after the blow is delivered. In the second case a blow of a set value is struck and cannot be altered unless the trip for the trigger is changed. Time is also lost in this method as the trigger block must fall to connect with the hammer which must again be hoisted before the next blow can be delivered.

The weight of the hammer used with any rig should at least equal the weight of the pile; and best results are obtained when the ratio is about 2 to

1 in favor of the hammer, so that the pile will be driven into the ground after FIG. 20.-Vulcan drop hammer, Vulthe inertia of the pile has absorbed its portion of the hammer energy. can Iron Works, Chicago, Ill.

The

fall should, however, not be too great as time is thus lost between blows.

Better results are obtained with a heavy hammer falling a short distance than with a light hammer falling a long distance. An average weight for a hammer is 3000 lb., and falls vary from 5 to 20 ft.

Steam Hammers.-A steam hammer is one in which the ram is actuated by steam. Steam hammers may also be operated with compressed air, but where air is used, larger exhaust openings are required to give the most efficient service.

The hammer is divided into two parts, the frame and the striker. The frame is attached