shall be adequately and securely protected against cave-ins,
displacement of the surrounding earth, and retention of ground
water, by means of temporary steel casings. Casings shall have
outside diameters not less than indicated shaft sizes, shall be a
minimum of 6.4 mm 1/4 inch thick, and shall not be removed if the
structural integrity of the caisson will be impaired, as
determined by the Contracting Officer. Temporary steel casings
shall be withdrawn, as the concrete is being placed, maintaining
sufficient head of concrete within the casing to prevent
extraneous material from falling in from the sides and mixing with
the concrete. Casings may be jerked upward a maximum of 100 mm 4
inches to break the bottom seal, but thereafter shall be removed
with a smooth, continuous motion.
c.
The inside of steel casings shall be thoroughly cleaned and oiled
before reuse.
d.
The temporary casing shall be in place from the caisson top to the
ground surface until the concrete has set if the elevation of the
top of the caisson is below the adjacent ground surface.
e.
The outside diameter of permanent casing shall be the same as the
nominal shaft diameter. Wall thickness of permanent casings shall
be a minimum of [_____] mm inches.
f.
Water that flows into the excavations shall be continuously
removed and all water shall be removed from the excavation bottom,
to the extent possible, prior to concrete placement. The maximum
permissible depth of water will be 50 mm 2 inches. In the event
of a severe water condition that makes it impossible or
impractical to dewater the excavation, concrete shall be placed
using underwater tremie after water movement has stabilized.
g.
The bottoms of excavations indicated to be "belled" shall be
enlarged to diameters and shapes shown. Bells shall be excavated
or drilled in a similar manner to that used for shafts.
h.
The excavations for caissons indicated to be ["ribbed"] [_____]
shall be of the dimensions and shapes indicated.
i.
Each caisson excavation will be inspected and approved by the
Contracting Officer prior to placing concrete. A record of all
inspections, with related construction changes, shall be kept by
the Contractor. The Contractor shall provide support personnel
for inspection and testing procedures.
3.2
INSTALLATION
a.
Concrete shall be continuously placed by methods that ensure
against segregation and dislodging of excavation sidewalls, and
shall completely fill the shaft. Concrete shall be placed by
pumping or drop chutes in dry holes and by tremie or pumping in
wet holes. The discharge shall be kept a minimum of 1 m 3 feet
below the fresh concrete surface during placement. Drilling of
caissons or driving of casings shall not be within 6 m 20 feet of
concrete placed within the last 3 days.
b.
Concrete shall be brought to a true level surface inside the shaft
and a full width cross key formed, or dowels installed, should it
SECTION 02466A
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