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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.

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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.

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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 jackhammers. 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 1/2-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 60o 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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CHAPTER VI--TEST INSTALLATIONS

38. Purpose of Test Installations. The properties of all earth materials can be accurately determined in the laboratory for various working conditions. The designer of modern earth structures uses the results of these laboratory tests to design and analyze the structure. In addition to making tests on the fill to control embankment construction, elaborate test apparatus are installed in most dams now built by the Bureau to determine the behavior of the earth embankment and appurtenant structures during construction and later reservoir operation.

Piezometer installations are designed to contact, transmit to terminal wells, and record pore water pressure in the embankments and foundations of earth dams. Embankment settlement installations provide a means of measuring the consolidation within the embankment, settlement of foundation, lateral displacement of the embankment, and seepage through the embankment. Surface settlement installations are made to record cumulative settlement of the surface of the embankment and horizontal deflection normal to the axis of the dam.

In O'Sullivan Dam, 36 piezometer tips, 2 embankment settlement installations, and 66 surface settlement points were installed.

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A. Installation of Test Apparatus

39. General. According to a provision in specifications No. 1400 it was contemplated that the Government excavate the embankment material and place the settlement-measuring apparatus in position after the completion of each 5-foot lift of the embankment. The contractor was then to backfill and compact all excavated material around the apparatus. However, upon curtailment of the Government force-account activities it became necessary to make arrangements with the contractor for the excavation and backfill work in connection with the piezometer and embankment settlement apparatus installations. The work involved in establishing the surface settlement points was performed by Government forces.

40. Piezometer Apparatus. The piezometer installation at O'Sullivan Dam consists of 36 tips. Thirty-three tips are located at station 170+00 at various elevations and axis offsets and one tip each is located at an elevation of approximately 970 at stations 168+00, 172+00, and 174+00 (fig. 29). These piezometer tips are connected by 1/4-inch outside-diameter plastic tubing to gages in a terminal well 270 feet downstream from the axis station 170+03. When practicable the tubing was cut to the prescribed length extending from the tip to the well. Where lengths of tubing had to be joined, brass flared-type couplings were used. Trenches for the tubing and tips were dug a minimum of 2 feet deep (fig. 30) to insure adequate protection during the backfilling operations. It was found that the trench could be dug to adequate depth and to a reasonably true grade with a road patrol grader, followed by widening and trimming of the bottom and ends of the main trenches and digging of the side trenches for the tips by hand. Loose backfill material was hand placed directly in contact with the tubing and tips, after which it was rolled with the wheels of the grader. Thereafter, the grader was used to place and also compact the backfill material. To limit seepage at lower levels a small amount of bentonite was placed around the tubing at several points along the main trench between side trenches in zone 1 material. Although not considered to be necessary in this material, the bentonite was used as a precautionary meas

ure.

Tubing from tips; located in the cutoff trench, was brought to the original ground elevation in sloping trenches dug in the downstream slope of the cutoff trench. These sloping trenches were filled with compacted zone 1 material. Four to six inches of selected fine material was placed around the tubing where the trench for tubing passed through gravelly material. The tubing passes through the entrance pipe into the terminal well. The entrance pipe was filled with bentonite and sealed on each end with oakum and calking compound to prevent any leakage of moisture around the tubing into the well.

The terminal well, constructed of reinforced concrete, is 4 feet 5 inches by 5 feet 8 inches in plan and 27 feet deep. In the terminal well manifold system, 1/4-inch

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