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Figure  12-49.Typical  pile-driving  operation.
Underhung  Leads

Equipment Operator Basic - Beginning construction equipment operators manual
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steel sheetpilings. Figure 12-51 shows the components of a swinging lead. The boom point sheaves are used to accommodate the  hoist  drum  wire  rope  that  supports  the  pile, pile-driving  hammer,  and  leads;  therefore,  its  use requires a three-drum crane. Under certain conditions a two-drum crane can be used The leads are raised to the vertical by a combination of booming, swinging, and/or  traveling. ADVANTAGES.—  Some advantages of using a swinging lead over other types of leads are as follows: 1.  They  are  the  lightest,  simplest,  and  least expensive. 2.  With  stabbing  points  secured  in  the  ground, these leads are free to rotate sufficiently to align the pile-driving  hammer  with  the  pile  without  precise alignment of the crane with the pile. 3. Because these leads are generally 15 to 20 feet shorter than the boom, the crane can reach out farther if the crane has sufficient capacity. 4. They can be used to drive piles in a hole, ditch, or over the edge of an excavation. 5.  For  long  lead  and  boom  requirements,  the weight of the leads can be supported on the ground and Figure 12-52.-Lead adapters connected to the boom tip. DISADVANTAGES.—   Some  disadvantages  of using a swinging lead are as follows: 1. It requires a three-hoist drum crane (main line for the pile, secondary for the pile-driving hammer, and third for the leads) or two-hoist drum crane with the lead hung on the sling from the boom tip. 2. Because the leads are supported by the hoist wire rope, precise positioning of the leads with the top of the pile is difficult and slow. 3.  If  stabbing  points  are  not  secured  to  the the   pile   is   lifted   into   place   without   excessively ground,  it  is  difficult  to  control  the increasing the working load weight. leads. twisting of the Figure 12-51.-Swinging leads. 12-38







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