excavation bottom prior to concrete placement. The maximum permissible
water depth will be 50 mm 2 inches at the start of concrete placement. If
severe water conditions make it impossible or impractical to dewater the
excavation, deepen the excavation to undisturbed material and place
concrete using underwater tremie after water movement has stabilized.
3.1.3
Filling
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NOTE: The criteria of placing concrete within 3
hours should be modified with agency requirements.
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Prior to placing concrete, inspect caisson excavation to ensure that
deleterious material or detrimental conditions are not present in the
excavation. Concrete shall be placed within 3 hours after completing
excavation. Place concrete continuously by methods that ensure against
segregation and dislodging of excavation sidewalls and completely fill the
bell and shaft. Place concrete by pumping, tremie, or drop chutes. For
concrete placed by pumping or tremie, the discharge shall be kept a minimum
of 914 mm 3 feet below the fresh concrete surface during placement.
3.1.3.1
Keys for Placement in Lifts
Bring concrete to a true level surface inside the shaft and form a full
width cross key or install dowels should it become necessary to interrupt
placing concrete in any caisson. Prior to placing additional concrete,
clean surfaces of laitance and slush with one to one portland cement grout.
The grout shall have a water cement ratio not exceeding that of the
concrete.
3.1.3.2
Chute Placement
Place concrete in dry batter caissons with a drop chute extending within
914 mm 3 feet of the concrete surface in the excavation.
3.1.3.3
Concrete Vibration
Vibrate concrete for full height of caisson for caissons without permanent
encasing. For caisson, with permanent encasing, vibrate only the bell of
the caisson.
3.1.4
Reinforcement
Install as indicated. Insert securely in the caissons, in position and
alignment, as shown, [prior to concrete placement] [prior to the concrete
reaching an elevation [_____] m [_____] feet below the bottom elevation of
the reinforcement].
3.2
TOLERANCES
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NOTE: Tolerances should be correlated with design
criteria and types of caisson.
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3.2.1
Alignment
Caissons out of center or plumb beyond the tolerance specified shall be
SECTION 02468N
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