Section 27-703
§ 27-703 Exceptions. The provisions of sections 27-704 and 27-705 of
this article shall not apply to piles driven with a vibratory hammer or
other equipment wherein the energy of impact cannot be evaluated.
Section 27-704
§ 27-704 Equipment. (a) General. The hammer shall travel freely in the
leads. The cushion or cap block shall be replaced, if crushed. The
hammer shall deliver its rated energy, and measurements shall be made of
the fall of the ram or other suitable data shall be observed at
intervals as required to verify the actual energy delivered at the
termination of driving.
(b) Cushion or cap block. The cushion or cap block shall be a solid
block of hardwood with its grains parallel to the axis of the pile and
enclosed in a tight-fitting steel housing, or shall be an equivalent
assemblage. If laminated materials are used, the type and construction
of these materials shall be such that their strength is equal to, or
greater than, hardwood. Wood chips, pieces of rope, hose, shavings, or
automobile tires and similar materials shall not be used. Cap blocks
shall be replaced if burned, crushed, or otherwise damaged.
(c) Followers. Followers shall not be used unless permitted in writing
by the architect or engineer, and only when necessary to accomplish such
installation. They shall be of steel or hardwood of such size, shape,
length, and weight as to permit driving the pile in the desired location
and to the required depth and resistance. The required driving
resistance tabulated in Tables 11-4 and 11-5 shall be increased to
compensate for the loss of energy in the hammer blow. The follower shall
be a single length section, shall be provided with a socket or hood
carefully fitted to the top of the pile to minimize loss of energy and
to prevent damage to the pile, and shall have sufficient rigidity to
prevent "whip" during driving.
Section 27-705
§ 27-705 Procedures. (a) Continuous Driving. Driving of piles
preliminary to final seating shall be continuous for an interval
adequate to break or prevent the development of freeze. The hammer shall
be operated at its rated speed during this interval.
(b) Jetting. Jetting, augering and other methods of pre-excavation
shall not be used unless permitted in writing by the architect or
engineer. When permitted, such procedures shall be carried out in a
manner which will not impair the carrying capacity of the piles already
in place or the safety of existing adjacent structures. Jetting or
augering shall be stopped at least three feet above the final expected
pile-tip elevation and at least three feet above the tip elevation of
any pile previously driven within six feet of the jet or auger, except
that where piles are to be end bearing on rock or hardpan, jetting or
augering may be carried to the surface of the rock or hardpan. Piles
shall be carried down beyond the depth of jetting, augering or other
pre-excavation until the required resistance is obtained. If there is
evidence that jetting or other procedures have disturbed the
load-bearing capacities of previously installed piles, those piles that
have been disturbed shall be restored to conditions meeting the
requirements of this article by redriving or by other methods acceptable
to the architect or engineer. Redriving or other remedial measures
shall be instituted after the jetting or other operations in the area
have been completed.
(c) Sequence of installation. Individual piles and pile groups shall
be installed in such sequence that: (1) the carrying capacity of
previously installed piles is not reduced; (2) the soil surrounding the
piles is not compacted to the extent that other piles in the group
cannot be installed properly; and (3) ground movement that would damage
adjacent buildings or utilities is prevented. In general, in any group,
driving shall start from one side and proceed progressively toward the
other side of the group or shall start from the middle and proceed
toward the edges of the group.
(d) Heaved piles. In soils in which the installation of piles causes
previously installed piles to heave, accurate level marks shall be put
on all piles immediately after installation, and all piles that have
been heaved by an amount in excess of one-quarter of an inch shall be
redriven to the required resistance.
(e) Penetration measurements. Penetration measurements made for the
purpose of determining resistance to driving shall not be made when pile
heads are damaged to an extent that may affect measured penetration, nor
shall they be made immediately after fresh cushion blocks have been
inserted under the striking part of the hammer.