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faster operation, was much more effective and economical than the commercial machine. The use of the commercial machine was discontinued after the first 3 weeks of use and the converted jackhammer was used exclusively for the remainder of the job.

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Figure 24. --Hand tamper for compacting zone 1 mate-
rials where a sheepsfoot roller could not be used.
This machine was made from a jackhammer by re-
moving the ratchet shoe and fastening a flat steel shoe
to a piece of drill steel which was fitted into the chuck
of the jackhammer. 2106-4 9-16-48

When elevation 922 was reached at station 170+00, the zone 1 material was sloped to form a ditch. When the other zones of material had also been placed to elevation 922, water was allowed to flow across the dam through the ditch in the zone 1 material. Placement operations were halted until the completion of the outlet works tunnel and installation of the 4- by 4-foot gate, after which the flow of water was diverted through the tunnel and normal construction activities were resumed.

(c) Zone 2. --Placement of zone 2 material followed the same general pattern as that orzone 1. It was found experimentally that a mixture of one part of silty material and four parts of pit-run gravel and sand resulted in a satisfactory zone 2 material. This material was processed and compacted in a manner identical to that used in zone 1. Because of the porosity of the outer edge of zone 1 material the contractor was required to make a one-blade-width cut. with a bulldozer at the line of contact of zones 1 and 2, so that when additional zone 2 material was placed, it would be bonded to zone 1 instead of lying against a porous layer of material.

(d) Modifications. --During construction of the dam embankment it became necessary To reviselfie location of the various zones above elevation 1047. According to the original plans the outside slope of each zone was to continue on its prescribed slope to elevation 1059. 5. This resulted in such narrow working spaces between zones that proper placement and processing operations were not possible. At about elevation 1047 placement of zone 2 material was discontinued, zone 1 material was widened to cover zone 2, and the outside slopes of this widened zone were made 2-1/2 to 1 on the upstream and 2 to 1 on the downstream sides of the embankment. At elevation 1056 placement of zone 1 material was discontinued and only zone 3 material was placed from that point to elevation 1059. 5 which was the subgrade for the roadway. Above elevation 1053 the outside slopes of the zone 3 material were changed to 1-1/2 to 1. This change in slope widened the top of the dam sufficiently to permit

the curbing of the roadway to be placed in gravel instead of coarse rock as would have been necessary prior to the change in zones and slopes.

(e) Rock Surfacing. --The outermost zone of materials on the dam is a blanket of rock 2~feeT thick" on the downstream face of the dam and 3 feet thick on the upstream face of the dam. The rock surfacing was placed against the zone 3 material and followed the same slope as the outer slope of zone 3. On the downstream face (fig. 25) the rock was hauled by dump trucks which dumped the material from the top of the fill. On the upstream face (fig. 26) the rock was placed in a series of long piles whose long axes were approximately at right angles to the dam axis.

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Figure 25. --Placing the downstream rock blanket on a 2 to 1 slope by dumping from the top of fill. 2107-4

35. Moisture Control. - The moisture content of the material placed in zones

1 and 2 was of prime importance. This content was required to be not more than 4 percent below or more than 2 percent above optimum, optimum being the percentage of moisture at which maximum density of the material could be obtained with tamping. The optimum moisture varied with each type of material. A table was prepared for use by the inspectors showing the average optimum moisture content with corresponding Proctor needle reading for each type of material within a borrow area. Proctor needle penetration tests were made at the fill to determine the moisture content. If the moisture content was low, the contractor was required to add moisture to the material, scarify, remix, and reroll the lift. Material from the borrow areas that was too dry was conditioned before compacting by passing a sprinkler wagon over the dry area. The contractor used a large disk harrow and a rake (fig. 27) for aerating the material or for mixing water with dry material. After the optimum moisture content had been obtained, the material was compacted either by tamping roller or hand tamping.

C. Outlet Works

36. Excavation. - Work on the tunnel was started after the stilling basin had been excavated. Blast holes in the stilling basin and outlet portal were drilled with jackhammers; and after blasting, the shattered material was removed by a bulldozer.

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Figure 26. --Placing upstream riprap on face of zone 3 material. Bulldozers were used to smooth the rock from the rock piles which were dumped on the sloping surface of the dam. 2182-4 10-19-48

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Figure 27. --Equipment for processing zone 1 material. The disc harrow and rake are used for mixing the material to distribute evenly the moisture throughout the lift. 644-4 7-21-47

The tunnel excavation work was conducted on a two-shift basis--one for drilling and shooting, 8 hours allowed for the air to clear, and one shift for mucking. The shattered rock was loaded into a steel car by a small pneumatic mucking machine. The loaded car was run out by gravity, emptied into a dump truck, and then pushed back by hand. The open-cut portion of the tunnel (upstream end) was also drilled with jackhamiriers. After blasting, the shattered rock was removed by a power shovel. The rock encountered in the tunnel was basalt, ranging in nature from slightly vesicular to relatively dense. The dense basalt, columnar in formation, resulted in a large amount of overbreak. In spite of the overbreak, timbering of the roof of the tunnel was necessary only in one place where a slip was encountered.

The gate chamber shaft was excavated from underneath and as a result all excavated material fell into the gate chamber. The excavated material was loaded into steel cars which were also used for hauling out excavated material during the tunnel excavation.

While the last 100 feet of the tunnel was excavated, the open excavation for the inlet portal was started. The excavation for the trashrack structure revealed that there was a layer of shattered rock on top of a thick layer of interflow material. This condition necessitated the use of mass concrete for the trashrack foundation. Change order No. 4 was issued authorizing the contractor to use mass concrete for this purpose.

37. Concrete Placement. - When the excavation was completed, the concrete batching, mixing, and placing equipment (fig. 28) was assembled around the inlet portal. A four-bin manually operated batcher was constructed on top of the cliff above the portal and a l/2-cubic-yard mixer was placed on a platform so that the batcher discharged by gravity directly into the mixer.

In carrying out the tunnel lining operation, the contractor began at the roundto-square transition at the upstream side of the gate chamber. Reinforcement steel was placed in the tunnel for a length of 120 feet upstream from the gate chamber. Concrete was placed in the bottom 60° of the circumference of the tunnel lining from the transition to the inlet portal by use of a screed. The remainder of the circumference was placed by use of 25-foot-long forms. During the placing of the arch section the temperature was 40° F. and less, so the form stripping time was held to 24 hours.

Prior to concrete placement in the portion between the gate chamber and outlet portal, the 22-inch steel pipe was securely fastened in place. This pipe was embedded in concrete under the tunnel invert. After completion of the tunnel lining operations, 2inch weep holes were drilled through the lining downstream from the gate chamber for relieving outside hydrostatic pressures.

The gate chamber and shaft were constructed monolithic with the tunnel lining. They were constructed of reinforced concrete throughout. A steel form was used for the inside and no outer form was used until the shaft came out of the ground. Above ground an octagonal form, constructed of wood, was used. In lining the shaft, a gallows frame was constructed on top of the shaft and the concrete lowered in a bucket to the point of placement.

The placement of concrete for the trashrack was carried on concurrently with the construction of the gate chamber and shaft. Mass concrete was used for the trashrack foundation, as previously mentioned. After the forms from the gate chamber were stripped, the 18-inch valves and the 4- by 4-foot gate with hydraulic operating equipment were installed and the final concrete poured around them.

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