ETL 1110-2-355
31 Dec 93
during the construction process is crucial for the
c. The general shape of a monolith's bearing
successful long-term operation of the equipment and
pressure diagram is characteristic for differential
to minimize disturbances to construction.
settlement between the walls and the base slab. Con-
crete placement sequence also affects the differential
8-6. Silt. Silt accumulations upstream of miter
settlement of the monolith.
gates and in the lock chamber may become an opera-
9-3. Reinforcement placement. Proper rein-
tional problem. Large accumulations of silt can
restrict the free movement of the miter gates. There
forcement detailing will simplify congested areas,
are several methods available for removing silt from
ensure ease of reinforcement placement, and facilitate
around miter gates. Blockouts may be used upstream
the placement of concrete.
of the gates to provide more area for silt to accumu-
late in before it must be removed. A silt flush sys-
a. Congestion. (See reference ACI 309.3R for
tem using water may be installed to resuspend the silt
related discussion.)
in the water and move it out of the gates' path.
Small-diameter pipes can be placed in the lower gate
(1) U-frame locks generally have small amounts
sill to provide for flushing action around the lower
of reinforcement in relationship to the volume of
miter gates.
concrete; however, reinforcing is concentrated at the
concrete faces. Reinforcement layering and bundling
of bars can reduce congestion; however, additional
9. Constructability Considerations
layers of horizontal reinforcement can create difficul-
ties in the placing of concrete and bundled bars have
9-1. General. A U-frame lock design includes
characteristics (ACI 318) that may make them
undesirable.
details that ensure structural performance and can be
accurately detailed, bid, and constructed. Good
(2) Possibly the most congested area of rein-
detailing will be rewarded by reducing contract
forcement is at the intersection of the base slab and
modifications and reducing engineering effort when
the lock wall (particularly for culvert intake and
interpreting the plans for field personnel and the
discharge manifolds). At this location, wall dowels
contractor. There are some areas that are trouble-
intersect and may conflict with the layers of base slab
some, and these will be briefly discussed in the fol-
reinforcement. Generally, main structural reinforce-
lowing paragraphs.
ment should be located first and less important rein-
forcement spaced to eliminate interference. For
9-2. Construction sequence for monoliths.
example, the placement of vertical reinforcement in
the lock wall may be dependent upon missing voids
a. Typically two monoliths will be constructed
or embedded items encountered higher up in the wall.
separated by a space for a third monolith. The mid-
It follows that base slab reinforcement should be
dle monolith will use the end monoliths as formwork
detailed, to scale, to avoid the vertical lock wall
and as supports to which joint material can be
reinforcement. Other items which may contribute to
attached. Expansion joint material must not be com-
congestion are heavy structural steel for support of
pressed by the fluid force of fresh concrete, but must
reinforcement, electrical conduits, instrumentation,
be compressible to accommodate thermal expansion
embedded metals, heavy reinforcement requirements
of the monoliths.
at ports/manifolds, and formwork supports.
b. Construction sequencing of the monoliths
(3) The contractor may opt to set the ends of
should be to place the deeper founded monoliths first.
wall vertical bars at the top of concrete lifts instead
This eliminates potential undermining and loss of
of holding them up at elevations as specified on the
foundation confining soil during excavation if the
drawings. Although this is generally allowed, the
more shallow monolith were placed first. Backfilling
additional reinforcement may add to the congestion.
of overexcavation for the deeper founded monoliths
should be done prior to placing concrete for the adja-
cent monolith.
A-31
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