ETL 1110-2-343
31 May 93
limit water seepage. Joint sealants have also been
used with precast panels and other formed joints to
effectively limit water seepage. Precast concrete
panels are shown in Figure 1-14. Precast stay-in-
place concrete panels give a conventional concrete
appearance to the RCC structure. These forms are
anchored to the RCC by straps or rods and are
quickly and easily erected during construction.
Concrete at the upstream and downstream faces of
Upper Stillwater Dam was a conventional curb-type
facing concrete placed using a slipformer. The
conventional concrete was placed in approximately
2-ft-high sections at the upstream and downstream
Figure 1-11.
Placement of conventional con-
edges. After curing for 4 hr, the conventional con-
crete facing
crete provided the form boundaries between which
the RCC was placed and consolidated. At the
upstream face, the slipformed sections were placed
one on top of another, producing a vertical wall. At
the downstream face, the slipformed sections were
stair-stepped at the spillway section to dissipate
hydraulic energy and to reduce cavitation problems
associated with high-velocity flow.
(4) Other facing systems such as steel
sheetpiling, or a combination of conventional and
precast concrete panels, may also be used. An
example of an unformed (D/S) surface finish is
shown in Figure 1-15. The RCC shown was
allowed to assume a natural angle of repose on the
Figure 1-12. Final consolidation accomplished
downstream face of the gravity dam. The angle of
with vibratory roller
repose ranges between approximately 45 and 55
deg. The outer portion of the RCC at an unformed
surface is not fully consolidated and therefore is of
little structural value. The ragged and uneven
appearance of an unformed face may be improved
by trimming the loose RCC.
i. Special surface treatments for erosion
protection.
(1) General. Concrete erosion is a major con-
cern and must be considered when designing spill-
way aprons, stilling basin channels, and other con-
crete surfaces subject to high velocity flows, or
when designing concrete surfaces exposed to the
Figure 1-13. The conventional concrete facing
action of abrasive materials, such as sand, gravel, or
gives a conventional concrete appearance to
other waterborne debris. Erosion damage of con-
the RCC structure
crete surfaces can be caused by cavitation or
abrasion.
system. Several dams have been successfully
(2) Cavitation erosion. Cavitation from sur-
constructed using a high-density polyethylene liner
backing in conjunction with the precast panels to
face imperfections has been known to cause surface
1-11
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