steel sheetpilings. Figure 12-51 shows the componentsof a swinging lead.The boom point sheaves are used to accommodatethe hoist drum wire rope that supports the pile,pile-driving hammer, and leads; therefore, its userequires a three-drum crane. Under certain conditionsa two-drum crane can be used The leads are raised tothe vertical by a combination of booming, swinging,and/or traveling.ADVANTAGES.— Some advantages of using aswinging lead over other types of leads are as follows:1. They are the lightest, simplest, and leastexpensive.2. With stabbing points secured in the ground,these leads are free to rotate sufficiently to align thepile-driving hammer with the pile without precisealignment of the crane with the pile.3. Because these leads are generally 15 to 20 feetshorter than the boom, the crane can reach out farther ifthe 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, theweight of the leads can be supported on the ground andFigure 12-52.-Lead adapters connected to the boom tip.DISADVANTAGES.— Some disadvantages ofusing a swinging lead are as follows:1. It requires a three-hoist drum crane (main linefor the pile, secondary for the pile-driving hammer, andthird for the leads) or two-hoist drum crane with the leadhung on the sling from the boom tip.2. Because the leads are supported by the hoist wirerope, precise positioning of the leads with the top of thepile is difficult and slow.3. If stabbing points are not secured to thethe pile is lifted into place without excessivelyground, it is difficult to control theincreasing the working load weight.leads.twisting of theFigure 12-51.-Swinging leads.12-38
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