ETL 1110-2-355
31 Dec 93
8-3. Effects of voids. The use of voids or block-
Watertight joints to adjacent dam piers will change
the hydrostatic loads applied to the lock.
outs is acceptable. Voids and blockouts reduce the
weight of the structure as well as the loads on foun-
(2) Adequate joint thicknesses between structures
dation piling and/or foundation pressures. Voids or
permit them to maintain separation when deflecting
blockouts also reduce the amount of concrete needed.
under load. Guidewalls can have either a dead load
Using voids will increase the effort required to design
reaction or impact reaction on the lock.
and build the monoliths, but should result in less
expensive structures due to reduced concrete required
8-2. Seismic effects.
in the base and wall sections. Reducing the amount
of wall concrete will reduce the top base bending
a. In general, a U-frame lock is inherently seis-
moments, and possibly reduce the required base
mic resistant due to the lock symmetry (no torsion),
thickness. A means to remove seepage water from
monolithic shear wall and diaphragm action in void
the void must be provided or the seepage water
areas, integral foundation mat, wall aspect ratio, and
weight must be included in the monolith design.
overall rigidity. All of the above are benefits
achieved by good geometrical layout and proper
8-4. Foundation drains. Foundation drains
detailing of reinforcing. The main seismic weakness
beneath the lock and along the landwall of the lock
of a U-frame lock is the large base shears transferred
are used to reduce the piezometric head from seepage
to the limited foundation lateral load resisting system.
from the upper pool to the lower pool. The founda-
tion drains beneath the lock monoliths may be french
b. Structures adjacent to the lock should have
drains, consisting of either select sand or select sand
sufficient separation (joint width) from the lock such
with filter drains. These drains are usually connected
that the two structures will not strike each other dur-
to the lower pool with no control on backflooding.
ing a seismic event. Deflections used to size joint
Drains along the lock landwall are used to reduce the
thickness are computed using concrete gross section
horizontal hydrostatic load acting against the lock-
properties since the members are expected to remain
wall. Such drains consist of horizontal runs of well-
in the elastic range. Cracked section properties will
screen or perforated pipes connected to vertical clean-
be used if seismic analysis of the frame indicates a
outs and manholes. Means of preventing backflood-
nonlinear response.
ing through the drains should be incorporated into the
drain design. If the drain is relatively deep in rela-
c. The service bridge seats must have sufficient
tion to the height of the lockwall, it is recommended
bearing length (pinned ends) to accommodate the
that stainless steel wellscreen and pipe be used for the
largest lateral movement experienced by the bridge
horizontal drain pipe. Reducing uplift during
piers combined with a reasonable assumption for the
dewatering by exiting foundation drains into the lock
thermal contraction of the bridge. Proper detailing
chamber and then removing the drainage with pumps
will ensure that the bridge remains seated during a
should also be considered. The effectiveness of
seismic event.
drains should be considered in analysis.
d. Lateral loads above large voids must be
8-5. Instrumentation. Instrumenting the lock
transferred to the mass below the void and foundation
structure and its foundation can serve two basic func-
using interior walls as shear walls or by frame action
tions. Site personnel can monitor performance while
if shear walls do not exist (i.e., culverts and galler-
the lock is in service, and design assumptions and
ies). To ensure ductile frame action during seismic
parameters can be verified. Some examples of data
loading, typical ACI reinforcement details (ACI 318)
that can be accumulated include uplift and pore pres-
should be reviewed for applicability. Contiguous
sures, monolith tilt and alignment, cofferdam-cell
concrete, perpendicular to analysis strips, provides
movements, concrete crack widths, and internal con-
joint confinement which will reduce spalling concrete,
crete temperatures. More information on instrumenta-
and therefore generally eliminate the need for special
tion for structures can be found in EM 1110-2-4300,
seismic detailing.
and more information on foundation instrumentation
can be found in EM 1110-2-1908. Many types of
e. It is necessary to check equipment anchorage
instrumentation exist which serve different purposes,
for the OBE since the lock must remain in operation
but all forms require planning for both design and
during and after this event.
construction. Consideration of instrument installation
A-30
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