ETL 1110-2-536
31 Dec 94
panels were anchored into the RCC with 8-ft coil
phenomenal extended set times and reasonable
rods (3/4-in. diameter) and end plates. Panels were
strength performance. This process proved to be very
used for the vertical faces of the stilling basin training
effective in reducing manpower dedicated to mortar
walls and for the above-grade vertical surfaces of the
placement and provided uniform coverage of mortar.
upstream face of the dam.
The retarder is a product originally developed to
delay the setting of concrete, in transit mixers, for
(5) Panels were placed in a checkerboard config-
extended periods of time.
uration so that intermediate panels were supported by
previously placed and anchored panels. This elimi-
(9) Placement began in the key trench, with a
nated the need for external bracing. The checker-
placement of 16 lifts, totaling 1,800 cu yd. The RCC
board method of panel installation is a very
was conveyed to the placement and dropped to the
economical panel system, however, tight alignment
rock or RCC surface by elephant trunk followed by
tolerances are difficult to achieve. The specified
dozer spreading and compaction. The placement area
alignment tolerances were purposely broad so that
then expanded to the stilling basin slab, with 12 lifts
such a panel installation system could be utilized.
averaging 1,400 cu yd. RCC was conveyed to load-
ers, and subsequently transported to the placement
(6) The sloping surfaces were to be a free-
location. Loaders traveled as much as possible on
formed RCC slope. In order to dress these slopes,
fresh RCC surfaces rather than the older surfaces that
the free slopes had to be trimmed with a backhoe
were being prepared for the next lift. Upon comple-
bucket periodically. This produced the relatively
tion of the stilling basin slab, the placement area
uniform appearance of the slope, and removed the
narrowed to 84 ft and continued to narrow as the
uncompacted RCC on the slope.
dam's height increased. The RCC lifts for the stilling
basin training walls were placed concurrently with
(7) RCC was conveyed from the plant to the
each lift of the dam placements.
placement and discharged directly into front-end
loader (Cat 980) buckets. The material was driven to
(10) Production rates averaged 50 cu yd/hr dur-
the specific placement location and dumped onto the
ing the early key placements and the upper lifts (in
uncompacted RCC surface. The dozer (Cat D4)
the upper section of the dam). Typical production
spread the material in 14-in. thick layers. Compac-
rates of 200 to 225 cu yd/hr were maintained during
tion was done with a 10-ton double drum vibrator
placement of the stilling basin and main dam lifts.
roller (Ingersol Rand DA-50), and supplemented with
The typical placing sequence was: 1) vacuum accu-
a smaller roller (Ingersol Rand DH-22). Edge com-
mulated debris, ponded water, and segregated aggre-
paction was done with a rammer (Wacker). Since
gate; 2) air clean the surface; 3) wet the surface;
Zintel Canyon Dam required only moderate shear
4) apply bedding mortar; and 5) place the RCC.
performance at the lift joints, bedding mortar was
applied to the lift joints to assure shear and tensile
(11) A drilling program commenced approxi-
strengths, and vehicle transportation on the surface
mately 6 months after completion of the RCC place-
was allowed to reduce project costs. This arrange-
ments. The purpose of the drilling was to remove
ment did not jeopardize the lift joint quality and still
6-in. diameter cores from the structure and the foun-
provided significant equipment cost savings.
dation to evaluate the actual engineering properties of
the RCC and the foundation rock. This testing pro-
(8) RCC was placed in lifts 12 in. thick and
vided excellent information for future design efforts
mortar was applied to each lift surface. To minimize
using RCC. The testing showed that shear cohesion
the impacts of mortar application, the contractor
of the RCC lift joints more than doubled with the use
formulated a system to pump mortar to the placement
of bedding mortar on the lift surfaces from 85 psi for
and shoot the mortar on the surface. The mortar mix
unbedded lifts to 205 psi for bedded lift joints. The
was modified with "a high range retarder" to produce
parent RCC containing no lift joint, tested at 290 psi.
C-3
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