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and conducting the safety program. The local Government engineers and inspectors were responsible to the resident engineer for enforcing safety regulations and having unsafe practices corrected. Following is the safety record of Lytle, Amis,and Green Company, for the entire construction period:

Exposure, man-hours worked 1, 576, 365

Number of accidents 99

Lost time, days 5, 776

Frequency rate 62.80

Severity rate 3. 66

26. Construction Equipment. - Following is a list of the principal items of construction equipment: " ~

Number ~ _" ~"'

of units Equipment Size

3 Power shovels 3-1/2 cu. yd.

3 Power shovels 2-1/2 cu. yd. 1 Power dragline 1-1/2 cu. yd. 1 Truck-mounted crane 1/2 cu. yd.

1 Front-end loader

4 Scrapers 12 cu. yd. 8 End-dump trucks 10 cu. yd.

22 Bottom-dump trucks 13 cu. yd.

6 Bottom-dump trucks 24 cu. yd.

8 General utility trucks 1 to 4 tons

4 Road graders

19 Crawler-type tractors

1 Bulldozer tractor

8 Water tank trailers 4, 000 gal.

5 Sheepsfoot rollers

9 Portable air compressors 500 c.f. m.

3 Portable air compressors 315 c.f. m.

1 Stationary air compressor 1,000 c.f. m.

4 Water pumps 2, 000 g. p. m. 4 Diamond drills

6 Grout machines

1 Rock-loading machine

1 Concrete mixer 1 cu. yd.

1 Pumpcrete machine

Miscellaneous small equipment, such as jackhammers, water line drills, blowers, power tampers, concrete vibrators, and shop equipment was also used.

27. Government Organization. - The key members of the Residency IV staff of the Government are listed below:

1 resident engineer

1 field engineer

1 chief inspector

1 office engineer

2 civil engineers

CHAPTER V--CONSTRUCTION

A. Excavation

28. General. - The principal features involved in the construction of O'Sullivan Dam were approximately 19, 000 feet of nearly continuous embankment of varying height up to approximately 160 feet above streambed, a concrete-lined outlet works tunnel with appurtenant structures near the east end of the dam, a 500-foot-wide open-'channel spillway between sections of the embankment, and a roadway extending along the full length of the crest of the dam. The dam consists of moistened and rolled embankments of clay, sand, silt, and gravel, with the outer section of sluiced gravel fill.

In January 1947, the excavation work was begun by the prime contractor for the dam foundation, and by the subcontractor for the outlet works. (See chapter IV for contract information.) Because of the length of the dam (fig. 5) and the comparatively small amount of water that needed to be diverted, the contractor was able to perform a considerable amount of excavation, grouting, and placement of fill in the embankment before diverting the water from Crab Creek. The operations for diverting the flow of the creek were begun by the contractor in July 1947.

29. Cutoff Trench. - The contractor began excavating at the staked top of the slope and continued downward on the prescribed slope until sound bedrock was reached. The cutoff trench began at station 15+00 and extended continuously to approximately station 143+00, resumed at approximately station 149+00, and continued to station 205+04. Unusual conditions encountered in several areas during excavation necessitated special foundation treatment. These areas are located approximately between the following axis stations 33 and 34, 43 and 63, 97 and 110, 115 and 130, and 167 and 176. Except at these areas, the excavation and foundation treatment methods employed were generally the same for the entire cutoff trench and the exposed rock was suitable for the dam foundation without further treatment. Excavation was accomplished by power shovels which loaded the material into end-dump trucks. The material excavated was unsuitable for use in the dam embankment because it consisted largely of sandy silt with a comparatively high percentage of large basalt boulders. It was therefore wasted at the direction of the Government inspectors. The depth of overburden ranged from a few inches to 15 feet.

When large areas of rock suitable for foundation of the dam had been exposed, the drilling (fig. 15) and grouting operation was started. In areas where the exposed rock was not suitable for dam foundation, additional excavation was required. Between stations 33+00 and 34+00, and stations 43+00 and 63+00, the exposed rocks ranged from a broken vesicular basalt to an interflow material. Holes were drilled in these areas to a depth at which the drill cuttings showed a better grade of rock, and were loaded with enough 40percent blasting powder to loosen the undesirable material. After the blast an examination disclosed that the loosened material could be used as zone 2 material and the contractor was directed to place it in the embankment adjacent to the excavation area. At station 97+00, interflow material was also exposed after removal of overburden. This area was drilled and shot under rigid inspection. The shattered material was suitable for zone 3 material and riprap and was stockpiled. When the loosened rock was excavated it was found that a general 1-1/2 to 1 slope had been formed, but owing to the way the rock broke, the slope was stepped instead of being comparatively smooth. Hand compaction of zone 1 material, after placement, was required in these sections (sec. 34).

From station 100+00 to station 110+00 the exposed bottom of the trench was extremely rough and irregular, being studded with rock hummocks. The contractor was permitted to smooth the bottom of the trench by blasting. This smoothing of the bottom permitted the zone 1 backfill to be rolled into place rather than hand tamped. Between stations 118+00 and 130+00 there was an overburden of silt and large boulders ranging in depth from a few inches to 15 feet. This overburden as well as the interflow material and vesicular basalt were removed. In removing this unsuitable material, it was found that it lay on top of solid basalt that sloped on approximately a 20° grade along the line of the trench from station 115+00 to station 122+00, leveled off between stations 122+00 and 127+00, and sloped down again on about a 20° grade to station 128+00 at elevation 925. At station 128+50, test drill holes were put down 20 feet but no solid rock was found. The contractor was directed to carry the bottom of the cut in overburden material from station 128+00 to the contact with solid rock at station 130+00. This area required special grouting treatment.

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The area between stations 167+00 and 176+00, known as the closure section, lies between two solid basalt abutments, the west at elevation 1000 and the east at elevation 1010. From station 170+00 to the east abutment, the bottom of the trench was very irregular, being marked with potholes 1 to 5 feet deep and 1 to 4 feet in diameter, and containing numerous hummocks of rock. This area was excavated at one point to elevation 836, the lowest for the entire excavation. The hummocks were blasted and, to eliminate extensive hand tamping, the contractor paved the bottom with a lean concrete mix of three sacks of cement to 1 cubic yard of aggretate (fig. 16).

30. Water Diversion. - The overburden was removed from the east (left) bank of the creek to the east aDutment down to the water table at elevation 905. A 12-foot wide channel was dug from a point where Crab Creek could be diverted about 2, 000 feet upstream from the closure section, directly across the foot of the west abutment at about elevation 935. The bulk of the excavation was in broken basalt so that blasting could be kept to a minimum. In one of these areas the nature of the basalt was such that blasting caused shattering of rock below ditch grade. This caused leaks in the ditch when the water was turned into the channel. To seal the leaks, the entire length had to be blanketed with silt. Where the ditch crossed the line of the cutoff trench, difficulty was encountered in preventing the water from seeping into the trench at such a rate as to impede backfilling.

Later in the operation, a fill was placed across the channel above the upstream toe of the dam so that the flow of water down the coulee would not flood the closure section. As excavation progressed considerable ground water seeped into the cutoff trench, and it became necessary to keep the excavation area sloped to a sump at a low point where two gasoline-engine-driven pumps disposed of the water.

When bedrock was exposed at the closure section, well points were driven vertically into the sides of the trench at points of maximum seepage in an attempt to prevent the water from interfering with backfilling the trench with zone 1 material. This being unsuccessful, a concrete retaining wall about 14 inches high was built on each side from the seepage points to sumps in the low point of the trench. A perforated 8-inch pipe, discharging into the sumps, was laid behind each wall. The sump on each side of the trench was a pothole in the rock, conveniently located at the low point of excavation. A similar system of drainage was used for the portion of the trench on the west abutment.

On the contact of rock at the upstream toe of the trench at station 68+00, a spring flowing approximately 2 cubic feet per second was encountered. A concrete retaining wall approximately 5 feet high and encompassing the spring and the west sump, was built to impound the water. The water was then pumped out.

B. Embankment Placement

31. Preparation of Foundation. - The first operation consisted of the removal of brush and coarse rock by scrapers and bulldozers. The stripping operation was more or less intermittent, being accomplished when the equipment was available or when necessity required. In the areas under the rock blanket and zone 3 portions of the dam, the contractor was required to strip off only the loose rock and brush. Where the foundation was of firm rock, the contractor thoroughly cleaned the area by removing the loosened rock by barring where necessary and blowing the area off with compressed air to remove all small particles of rock, sand, and other loose material. Earth foundation material had to be processed to attain the same density as required in the zoned material with which it is to come in contact. To do this, the contractor used water sprinkler trucks and thoroughly compacted the foundation area with tamping rollers or hand tampers.

32. Grouting. - Except for special treatment of certain sections, all grout holes were drilled along the center line of the cutoff trench at 20-foot centers. All drilling was done by use of a diamond drill except the first 3 feet of each hole which was drilled by percussion methods. The ultimate depth of each hole was determined by its location; that is, the holes at 60-foot centers were drilled alternately to 60 feet and 110 feet. Between these, holes were drilled on 20-foot centers 35 feet deep. The drills and grout machines were all pneumatically operated with air supplied by portable compressors.

The grout mixture was composed of water and cement. The water-cement ratio ranged by volume between 5:1 and 0.5:1. All holes were started on a 5:1 mixture at 50

pounds per square inch pressure and the water-cement ratio was changed, depending on the rate at which the hole accepted the grout. The grout machine shown in figure 17 is of the double-tub type. The first tub, used for mixing, discharged into the second tube, which was connected to a reciprocating two-cylinder grout pump.

[graphic]

Figure 17. --Grout machine used in grouting foundation of O'Sullivan
Dam. The machine has a 15-cubic-yard capacity and the pump is air
operated. The man in the background is standing near the hole being
grouted. 360-4 3-27-47

All holes were first drilled to a depth of 35 feet. A grouting pattern was then used so that adjacent holes were not grouted in sequence. As soon as practicable after grouting, the holes on 60-foot centers were drilled to a depth of 60 feet and grouted, after which the holes at 120-foot centers were drilled to a depth of 110 feet and grouted. Some of the areas varied widely in rock conditions. In these areas, various drilling patterns and different grouting procedures were used. Between stations 115+60 and 131+00, both tight and open rock were encountered and the holes were spaced at 10-foot centers. The holes in this area did not accept much grout--only an average of 2 cubic feet per linear foot of hole. The holes between stations 142+50 and 142+75, and those between stations 148+20 and 148+70 accepted a very large amount of grout. A mixture of blowsand, cement, and water was used in these areas to decrease the cost while providing a satisfactory grout mixture. In the spillway section the holes were located in the concrete cutoff walls at 40-foot centers, staggered between upstream and downstream walls. At the access shaft to the outlet works gate chamber 10 holes were drilled in a semicircular pattern.

Owing to the character of the rock in the bottom of the cutoff trench, a grout cap was placed only at each end of the closure section where there was spongy material. These grout caps were keyed into solid rock. Special care was taken in the grouting of these areas to insure against leakage.

In grouting the drains and sumps in the closure section, a mixture consisting of 1 cubic foot each of water, cement, and fine sand and 2. 56 grams of unpolished aluminum dust was used. This was pumped in under a maximum pressure of 50 pounds per square inch.

The rock pockets caused by overbreak in the outlet tunnel were filled with a mixture of sand, cement, and water. After the concrete had set, the tunnel grouting holes were drilled. The holes were spaced at 20-foot intervals along the centerline; four holes

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