Some difficulties with the slack carriers on the high-line cable slowed down placing operations. The carriers sometimes failed to space themselves properly along the butt lines and, when the space between slack carriers became too great and a bucket was dumped, one of the butt lines would drop down and become entangled in the other lines. Rapid discharge of the concrete from the bucket, with resultant oscillation, also contributed to this difficulty. The 8-cubic-yard buckets would occasionally fail to open and close properly, but this was never a major cause of delay.

Near the end of placing operations in the fall, the night temperatures fell to nearly 40° F. and ice would form in the air lines to the vibrators. This would reduce the frequency of vibration by as much as 30 percent and the depth of the individual layers of concrete would have to be reduced to insure complete consolidation. As the concrete encroached on the abutments, it became apparent that the method of placement initiated in 1960 allowed the exterior concrete mix to extend too far into the block, the line of the cableway becoming very skewed with the radial centerline of the block. The contractor was therefore required to cut down the thickness of the exterior concrete to a maximum of 10 feet as specified. This necessitated more careful scheduling of batches and movement of the tailtower when placing near the exposed faces of the abutment blocks.

The contractor was required to change the number of layers of concrete in each 7-1/2-foot lift from four to five at the beginning of the 1961 construction season. This change in placing, combined with increased vibration and more workable concrete, resulted in better consolidation of the mass concrete.

Figures 197 and 198 show the status of dam construction as of May 1961 and July 1961, respectively.

(b) Powerplant. -- The mass concrete in the powerhouse foundation was placed in essentially the same manner as the mass concrete in the dam. An elevated side-delivery hopper was used to transfer concrete from the 8-cubic-yard bucket to a 4- or 2-cubicyard bucket carried by a 200-ton-capacity crawler-mounted power crane because limited space on some placements precluded use of the 8-cubic-yard bucket.

The 2-cubic-yard buckets used in restricted space had manually operated gates. The 4-cubic-yard buckets were equipped with gates which were operated by compressedair rams. An airhose had to be manually attached to and detached from these buckets to operate the gate. The contractor nearly completed the first-stage concrete throughout the intermediate structure of the powerplant before winter protection became necessary. Approximately one-half of this concrete was placed directly in the forms by the cableway and one-half was placed using the transfer hopper and the power crane.

In November 1961, the contractor commenced enclosing the entire powerplant with polyethylene-covered panels supported by steel scaffolding. This enclosure was heated with unvented bottle gas heaters and provided excellent conditions for winter concreting work.

A temporary timber deck was placed over the structural steel roof framing of the powerplant and a transfer hopper erected on the deck. Concrete was batched in the small plant, mixed in 7-1/2-cubic-yard transit mixers, hauled to the loading dock downstream

from the batching plant, discharged into a 4-cubic-yard bucket, and transported to the transfer hopper by the cableway. Concrete buggies were used to transport the concrete from the transfer hopper to a tremie leading from the roof to another concrete buggy setting on a runway along side the top of the form. The concrete fell a maximum of 54 feet through this tremie with no evidence of segregation. The concrete was dumped from the second buggy directly into the form and consolidated with immersion-type vibrators.

(c) Tailrace Retaining Wall and Outlet Works. -- The two blocks adjacent to the powerplant in the river outlet concrete and the tailrace retaining wall were placed with the 8-cubic-yard buckets and the cableway. The other blocks could not be reached with the cableway and the concrete was transferred with the same equipment as that used for the powerplant. The concrete was placed in the forms and consolidated in the same manner as the mass concrete in the dam.

The concrete that had to pass through the transfer hopper exhibited some segregation of coarse aggregate when it reached the block. This was never excessive and presented no problem other than the need for scattering of some of the larger aggregate by hand.

Some interesting formwork is presented by the outlet works trashrack structure, as shown in figure 199.

Figure 199. --View looking down at upstream end of the cantilever
base for the outlet works trashrack structure before placement
of concrete. Note the contractor furnished steel cantilever trusses
which will be embedded in concrete. The workmen are about 150
feet above the base of the dam. P591-421-3486, August 31, 1961.

(a) Spillway Tunnel. --The contractor first placed the invert of the tunnel from station 4+86.7 to station 7+37.5, then placed the remainder of the barrel from station 5+18.3 to station 7+37.5, (See fig. 50 for approximate location of stations.) The contractor made two attempts to place this mostly horizontal section of the tunnel invert with a doubleacting pumpcrete machine located at the inlet portal, with the pumpline lying on the invert. However, apparently because of the long sloping line and the vertical bend, both of these attempts resulted in a plugged pumpcrete line shortly after pumping was commenced. The contractor therefore moved the pumpcrete machine to the outlet portal and no further difficulties of any consequence were encountered.

A traveling screed supported by railroad rails was used to shape the invert concrete. The screed was moved by reeling in a steel cable, anchored ahead of the screed, with a single-drum pneumatic hoist mounted on the screed. Concrete discharged freely from the end of the pumpcrete line approximately 6 feet ahead of the screed. Part of this was placed manually against the forward edge of the screed and into two small hoppers on each side of the screed. A 6-inch immersion-type vibrator was used to consolidate the concrete ahead of the screed below invert grade. Three-inch immersion-type vibrators were used in the two small hoppers and against the forward edge of the screed above invert grade.

The invert section between stations 4+27 and 4+86.7 was placed with the pumpcrete machine again located near the inlet portal of the tunnel. The pumpcrete line leading to the point of placement lay on the tunnel invert with a 22-1/2° bend approximately 60 feet upstream from the outlet end. Coarse aggregate separated from the concrete and plugged the line immediately below the 22-1/2° bend. This occurred twice before the line was filled and the concrete was moving in a continuous stream into the forms ahead of the

traveling screed. The placement was completed with no more delays. The contractor also successfully placed the invert of the tunnel in the vertical curve between stations 3+56.5 and 4+27.1 with the pumpcrete machine located near the inlet portal. These placements were fully formed and the concrete consolidated with immersion-type vibrators supplemented by two form vibrators. The form was removed 1 to 2 hours after placement was completed and the surface of the concrete was given a U-3 finish with power trowels.

When the contractor attempted to place the tunnel arch between stations 4+86.7 and 5+18.3 with the pumpcrete machine at the inlet portal, the pumpcrete pipe again became plugged with segregated aggregate. Accordingly, the pumpcrete machine was moved to station 4+00 inside the tunnel and supplied with concrete through an 8-inch-diameter pipe leading from a hopper at the inlet portal to the pugmill on the machine. A shield on the end of the pipe deflected the concrete downward into the pugmill. The above method was used to place concrete to station 3+56.5, the pumpcrete machine being moved up the incline as necessary.

Concrete in the section of the spillway tunnel between stations 3+38 and 3+56 (the lower portion of the steep incline) was placed as follows: The pumpcrete machine was located approximately 100 feet to the right of the spillway tunnel at station 0+50. The concrete was discharged from a transit mix truck by means of a chute into the pumpcrete hopper. The pumpcrete line was laid across the thrust block area and hung from the crown of the tunnel on rock bolts. The concrete was discharged directly into the placement at the crown of the tunnel. The concrete left the end of the pipe with high velocity which resulted in some segregation.

The above-described method was modified somewhat when placing the section between stations 3+20 and 3+38--in this reach, a section of pipe closed at the end and having an opening in the bottom was placed on the end of the pumpcrete line. The concrete discharged through the bottom opening into a wooden box which slowed down the discharge noticeably; however, the last 10 feet of the placement was made with this pipe and box removed. This method of placing the concrete in the spillway tunnel was rejected as unsatisfactory.

The section between stations 3+02 and 3+20 was started in the same manner as the previous one, but the contractor was asked to put a 14-inch-diameter sliding pipe over the end of the slickline and to keep it partially buried in the placed concrete for this placement. This method proved satisfactory and was used to place concrete to station 1+75. The pumpcrete machine was used to place concrete in the spillway intake structure between stations 1+50 and 1+75.

The pumpcrete machine, the cableway, a truck crane, or a combination of the three methods was used to place the concrete in the remaining placements of the spillway inlet structure.

E. Foundation Grouting, Drilling, and Drainage

173. Introduction. Flaming Gorge Dam is a thin-arch concrete structure 502 feet high with a crest length of 1,285 feet. The foundation rock was drilled and grouted, and foundation drainage was provided by holes drilled into the rock. The general plan followed in pressure grouting the rock foundations is outlined below:

(1) Drilling and grouting the rock foundations of the dam and spillway-intake structure through low-pressure, shallow grout holes designated as B-holes.

(2) Drilling and grouting the rock foundation of the dam and spillway-intake structure through high-pressure, deep curtain grout holes designated as A-holes.

(3) Drilling and grouting the rock surrounding the upstream and downstream portions of the spillway tunnel and around the diversion tunnel plug.

(4) Grouting the backfill concrete placed in the tunnels excavated for cutoffs in shale seams.