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Pile Driving Techniques
Waterfront Structures - 14044_295

Builder 3&2 Volume 02 - Construction manual for building structures
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when the pile is not in line with the fall of the hammer. Always make sure the fall of the hammer is in line with the pile axis. Otherwise, the head of the pile and the hammer may be severely damaged and much of the energy of the hammer blow lost. Excessive bouncing may be caused by a hammer that  is  too  light.  However,  it  usually  occurs  when  the butt of the pile becomes crushed or broomed, as when the  pile  meets  an  obstruction  or  penetrates  to  a  solid footing.  When  a  double-acting  hammer  is  being  used, bouncing may result from too much steam or air pres- sure. With a closed-end diesel hammer, if the hammer lifts on the upstroke of the ram piston, the throttle setting is probably too high. Back off on the throttle control just enough to avoid this lifting. If the butt of the timber pile has been crushed or broomed more than an inch or so, Figure 10-17.-Types of pile damage caused by overdriving it should be cut back to sound wood before you drive it any  more. Obstruction  and  Refusal When a pile reaches a level where 6 blows of a drop hammer or 20 blows of a steam or air hammer do not drive it more than an average of 1/8 inch per blow, the pile has either hit an obstruction or has been driven to refusal. In either case, further driving is likely to break or split the pile. Examples of typical damage are shown if figure 10-17. If the lack of penetration seems to be caused by an obstruction, 10 or 15 blows of less than maximum force may be tried. This may cause the pile to displace or penetrate  the  obstruction.  For  obstructions  that  cannot be disposed of in this manner, it is often necessary to pull (extract) the pile and clear the obstruction. When a pile has been driven to a depth where deeper penetration is prevented by friction, the pile has been driven to refusal. It is not always necessary to drive a friction  pile  to  refusal.  Such  a  pile  needs  to  be  driven only to the depth where friction develops the required load-bearing  capacity. Straightening Piles  should  be  straightened  when  any  mis- alignment is noticed during driving. The accuracy of timber piles. Figure 10-18.-Realigning pile by pull on a line to a winch. 10-10







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