Maintain sufficient pressure at the steam hammer so that (1) for
double-acting hammer, the number of blows per minute during and at the
completion of driving of a pile is equal approximately to that at which the
hammer is rated; (2) for single-acting hammer, there is a full upward
stroke of the ram; and (3) for differential-type hammer, there is a slight
rise of the hammer base during each downward stroke.
3.2.2
Driving Helmets, Capblocks, and Pile Cushions
3.2.2.1
Driving Helmets or Caps and Pile Cushions
**************************************************************************
NOTE: Insert minimum and maximum thicknesses for
pile cushion. An absolute minimum would be 75 mm 3
inches and the actual required thickness would
depend upon pile length, hammer energy, design load,
required final penetration resistance, and character
of subsurface material to be encountered.
Generally thicker blocks are required for longer
piles, larger hammers, and harder driving. A wave
equation analysis is useful in determining required
thicknesses for pile cushion. Minimum thickness is
to protect head of pile. Pile cushion should also
have a maximum thickness to ensure effective
driving. Select when pile cushion is to be
replaced. It is generally recommended that a new
pile cushion be used at the start of driving of each
pile.
**************************************************************************
Use a steel driving helmet or cap, including a pile cushion between top of
pile and driving helmet or cap, to prevent impact damage to pile. The
driving helmet or cap-and-pile cushion combination shall be capable of
protecting the head of the pile, minimize energy absorption and
dissipation, and transmit hammer energy uniformly over the top of the pile.
The driving helmet or cap shall fit sufficiently loose around the top of
the pile so that the pile may be free to rotate without binding within the
driving helmet. The Contractor shall demonstrate to the satisfaction of
the Contracting Officer that the equipment to be used on the project
performs the above function. The pile cushion shall be of laminated
construction using softwood boards with the grain parallel to the end of
the pile. The thickness of the pile cushion shall be 300 mm 12 inches
minimum. The cushion shall not be changed near the end of driving.
Replace the pile cushion when it has become compressed beyond two-thirds of
its original thickness, charred, or burned, or has become spongy or
deteriorated in any manner. Use new cushions for initial driving of each
pile. During redriving or restriking of piles, a used cushion assembly
shall be used. The Contractor shall submit to the Contracting Officer at
least 2 weeks before the start of pile driving operations detailed drawings
of the driving helmet and pile cushion to be used.
3.2.2.2
Hammer Cushion or Capblock
**************************************************************************
NOTE: Select either wood or aluminum/micarta
capblock. Delete inappropriate sentences. An
aluminum/micarta capblock is recommended because of
its consistent elastic properties and long life.
If final pile penetration resistance is based on a
SECTION 02395
Page 20
Previous Page
