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the vicinity of the work, all excavated material which was suitable for concrete was stored for such use.

On the south abutment the lava cap was entirely removed in order that the dam might be founded upon the underlying granite. This material, along with that not suitable for concrete, was deposited upstream and downstream from the dam site. The excavation of the abutments was carried on just ahead of concreting and was completed in November 1915.

Concrete work on the dam started in November 1912, and was completed in November 1915. The dam was virtually built in three sections. The first section, as indicated previously, was built to protect the subsequent work. It consisted of a portion of the dam along the upstream face to a height of about 40 feet above high water in the river, and of ample section to withstand water pressure to that height. The second section brought the full width of the dam to the top of the first section, and the third section completed the dam.

The best progress was made during the months of April, May, June, and July 1914, when more than 200,000 cubic yards of concrete were placed, an average of more than 50,000 cubic yards per month. In June 1914, 56,500 cubic yards were placed in 26 working days, an average of 2,170 cubic yards per day of two 8-hour shifts.

The aggregate for the first and second sections of the dam, 186,000 cubic yards, was obtained from the river-bed excavation. The remainder was hauled over the railroad from a gravel pit located near the Boise Diversion Dam 14 miles below Arrowrock.

The concrete used in the dam was composed of about 1 part sand-cement, 2){ parts sand, 5% parts gravel, and 3 parts cobbles passing a 5J£-inch grizzly. A somewhat richer mixture was used in the faces and upper portion of the dam and in the toe of the dam where the maximum stresses occur. A richer sand-cement concrete mix was also used in the spillway weir and lining. A straight portland cement concrete mix was used in the parapet walls, spillway piers, and other thin and heavily reinforced portions of the dam and spillway.

The sand-cement was composed of standard portland cement, with a little less than an equal amount of pulverized granite, reground to a fineness such that 90 percent would pass a No. 200 sieve. Besides the rigid fineness test, the sandcement was required to pass all the standard physical tests for portland cement. The concrete made of this sand-cement was slower in setting and hardening than that made with straight portland cement.

Two 12-ton cableways, each 1,500 feet long, with 60-foot stationary head towers, were installed in such a postion as to command the entire area of the dam. These cableways were operated by electric motors and were employed in excavating and in transporting equipment and materials for construction. Four 10-ton stationary derricks, two 6-ton

traveling derricks and several small stiff legs were also employed in excavating and handling materials on various parts of the dam and spillway.

A steam-operated, dragline excavator, with a 2%-yard bucket, was used for excavating part of the foundation of the dam. A 70-ton steam shovel, with a 2%-yard dipper, was used for excavating part of the dam foundation, for excavating the spillway, and for loading gravel at the Diversion Dam gravel pit.

The aggregate screening and crushing plant and the concrete mixing plant for constructing the first and second sections of the dam were located on the lava cliff on the south abutment, directly beneath the main cableways. The mixing plant was a 2-unit installation, consisting of 1-yard mixers electrically operated, each served with bins, measuring boxes, scales, and other pertinent equipment.

Material from the river bed suitable for concrete was taken by cableways directly to the screening and crushing plant, where it was processed and stored in stock piles. The aggregate was then hauled to the mixer bins by dump cars and scrapers. Concrete was discharged from the mixers into 2-yard stationary hoppers, from which it was delivered into specially made 2-yard buckets and then into movable hoppers, each suspended from the main and auxiliary cableways. The concrete was distributed from the hoppers into the dam by attached chutes, the free ends of which would be moved to any point desired.

Upon completion of the first and second sections of the dam, the mixing plant was dismantled, moved downstream, and located on the lava bench just below the dam. This plant was in all respects similar to the first one, except that it was a 3-unit installation, with three 1-yard mixers.

Aggregates for the second plant were hauled by railroad from the gravel plant at the pit near the Boise Diversion Dam, and deposited into storage bins above the mixers. The concrete was discharged from the mixers into 2-yard trolley cars and carried to a central distributing tower 150 feet high. From this tower the concrete was distributed by buckets and hoppers in the same manner as that employed in the first sections of the dam.

When construction neared the upper portion of the dam, the cableways could no longer conveniently cover the work on the long sweeping area, and the distributing system was changed. A track and dump-car system was employed, the track being supported on collapsible forms running the length of the dam. The concrete was conveyed from the mixers by the main cableways to hoppers placed at both ends of the dam, where it was carried to any point by electric dump cars running on the track. The track and hoppers were raised as the work progressed.

Concrete for the spillway was obtained from the second mixing plant, and was transported from the plant to a dumping hopper at the spillway site by one of the main cableways. The concrete was distributed from the hopper to the various parts of the work by chutes, dump cars, an auxiliary cableway, and a traveling derrick.

The sand-cement plant was located at the north abutment of the dam. The mill consisted of a rock crusher, a pair of sand rolls, a ball mill, and four tube mills. The plant had a capacity of 2,000 barrels of sand cement in a 24-hour period. After grinding, the sand cement was carried across the river by a 3-inch pipe pneumatic conveyor to the mixing plant. The sand-cement plant manufactured a total of 586,450 barrels of sand-cement. It was estimated that the savings effected by the use of the sand-cement over straight portland cement totaled approximately $300,000.

It is estimated that there are 3,000,000,000 feet of timber on the Boise River watershed above Arrowrock Dam. To provide a means for getting logs out of the reservoir, over the dam, and into the river again, a log conveyor was built at the south end of the dam. It was designed for a capacity of 60,000,000 feet of logs during a season lasting from May 1 to July 15.

The conveyor consists of a "lift" by which the logs are raised from the reservoir to a log deck by cable loops; live rolls across the dam; an endless chain chute 390 feet long on a 62.5 percent grade; and a gravity chute 245 feet long on a 32 percent grade. The structures are built of reinforced concrete and structural steel.

Construction of the log conveyor was started in March 1915, and finished in November 1915, with the exception of placing a small amount of machinery, which was completed in the early part of 1916.

The principal quantities involved in the construction of the log conveyor were 8,265 cubic yards of excavation, 2,134 cubic yards of concrete, 84,060 pounds of reinforcement steel, 300,390 pounds of machinery and structural steel, and 200 linear feet of tunnel.

1936-37 ALTERATIONS

During the 20 years since the dam was built, the downstream face of the dam, the spillway channel lining, and other exposed surfaces which were made of the sandcement concrete, have suffered some disintegration. This has been due, primarily, to the fact that the sand-cement concrete was very porous and absorbed water freely, resulting in rapid spalling with alternate freezing and thawing. It became apparent as early as 1927 that means had to be taken to protect the concrete surfaces from the action of water.

In 1935, $600,000 was made available for making repairs to the dam and spillway. Contract for construction was awarded to T. E. Connelly, Inc., of San Francisco, Calif., on January 10, 1936.

The repairs to the dam include an 18-inch reinforced concrete slab on the downstream face below elevation 3197.75, and a gunite covering on the remaining portion

of the face above that elevation. The concrete slab will be thoroughly drained by a network of porous-concrete drain tile. The spillway channel floor is being covered with a reinforced concrete slab and the side lining covered with a layer of gunite, reinforced with steel mesh. Incident to the repairs, as described previously, the dam and spillway crest are being raised and the automatic operating mechanism for the spillway gates altered.

In order to unwater the foundation and gain access to the downstream toe of the dam, a tunnel has been constructed, connecting two of the power outlets and one irrigation outlet in the lower tier of conduits with the existing diversion tunnel below the concrete plug. A cofferdam is being constructed upstream from the old diversion tunnel outlet and water for irrigation demands will be diverted around the dam through this tunnel.

COSTS

The cost of the original construction of the dam and appurtenant works was $4,796,489, subdivided as follows:

Preliminary surveys and examinations 58,720.61

Preliminary and general work (including foundation

testing, net cost of railroad, etc.) 177,172.37

Right-of-way 70,570.86

Water rights 20,041.78

Roads 76,486.72

Telephone system 9,675.20

Power plant and transmission lines 195,305.00

Dam (including construction camp, diversion works,

pumping, etc.) 3,611,048.51

Log conveyor and crane 63,560.64

Power outlets 19,451.36

Spillway 531,136.51

Bridge over spillway 3,749.04

Buildings (permanent) 9,570.22

4,796,488.82

Inasmuch as the work on the original dam was done by force account, accurate subdivisions for determining unit prices could not be made. Approximate unit prices, as determined for the major items of construction, were as follows:

Item Unit price

Diversion tunnel excavation $6.20 per cubic yard

Excavation for dam (all classes) SI.45 per cubic yard

Excavation for spillway $0.75 per cubic yard

Concrete in dam $4.00 per cubic yard

Reinforced concrete in spillway $7.50 per cubic yard

Structural-steel spillway gates and outlet con-
duits $0.08 per pound

Construction camp (construction and mainte-
nance) $225,000

Diversion works (complete) $350,000

Unwatering dam foundation $45,000

The work on the alterations to the dam and spillway, as of December 1, 1936, is about 40 percent complete. Approximately $235,000 of the $600,000 estimated to complete the project were expended up to that date.

BIBLIOGRAPHY

Bache, Reve. Government Runs Railroad to Build Biggest Dam. Technical World, May 1912, vol. 17, pp. 311-314.

Clawson, R. R. Messhouse Management at the Arrowrock Dam. Engineering News, June 24, 1915, vol. 73, pp. 1201-1203.

Cunningham, M. F. The Arrowrock Dam. Western Engineering, November 1915, vol. 6, p. 192 (see also Pacific Builder and Engineer, April 1916, vol. 21, p. 194).

Davis, A. P. Irrigation Works Constructed by the United States Government. John Wiley & Sons, New York.

Davis, A. P., and Wilson, H. M. Irrigation Engineering. John Wiley & Sons, New York.

Doll, M. G. The Arrowrock Dam. Mine and Quarry,
August 1913, vol. 7, p. 753 (see also Engineering Record,
September 6, 1913, vol. 68, pp. 265-267).

Ensign, O. H.:
Hydroelectric Plant for Construction Work (Boise Plant).
Engineering Record, Aug. 24, 1912, vol. 66, pp. 209-
211.

Large Balanced Valves for Reservoir Outlets. Engineering Record, July 11, 1914, vol. 70, p. 53.

Gaylord, J. M. How Water is Controlled at the Arrowrock Dam. Rec. Record, August 1916, vol. 7, pp. 359-360 (see also Engineering Record, Sept. 30, 1916, vol. 74, p. 409).

Hanna, F. W. Progress on Arrowrock Dam. Engineering Record, Mar. 7, 1914, vol. 69, p. 272.

Mayhew, A. B. Construction Camp at Arrowrock Dam. Engineering Record, Aug. 2, 1913, vol. 68, pp. 116-118.

Paul, C. H.:

Diversion Works for Arrowrock Dam. Engineering Record, Apr. 6, 1912, vol. 65, p. 368 (see also Engineering News, June 6, 1912, vol. 67, pp. 1061-1065; Eng. & Cont., Aug. 21, 1912, vol. 38, p. 218; Engineering News, Jan. 16,1913, vol. 69, pp. 118-120; Engineering Record. Feb. 22, 1913, vol. 67, pp. 214-215).

Sand Cement as Used by the United States Reclamation Service (Including costs). Engineering News, Mar. 20,

1913, vol. 69, pp. 562-563. (See also Engineering Record, Mar. 29, 1913, vol. 67, p. 343; Eng. & Cont., May 21, 1913, vol. 39, p. 571; Trans. Am. Soc. C. E., vol. 76, p. 560.)

Excavation for Arrowrock Dam, Idaho. Engineering News, July 17, 1913, vol. 70, pp. 93-100.

Excavation for Arrowrock Dam, Idaho. Water Power Chronicle, September 1913, vol. 2, p. 139.

Progress on the Arrowrock Dam. Engineering News, June 11, 1914, vol. 71, pp. 1286-1288.

Large Balanced Valves. Engineering Record, July 11,

1914, vol. 70, p. 53. (Short editorial, p. 31.) Concreting the Arrowrock Dam. Engineering Record,

Aug. 8, 1914, vol. 70, pp. 152-153.

Discussion of Grouting Arrowrock Dam. Trans. Am. Soc. C. E., 1915, vol. 78, p. 535.

Install Huge Balanced Valves at Arrowrock Dam. Engineering Record, Feb. 13, 1915, vol. 71, p. 208.

Log Handling Equipment at Arrowrock Dam. Engineering News, July 29, 1915, vol. 74, pp. 200-201. Paul, C. H. and Mayhew, A. B. Temperature Changes in

Mass Concrete (Diagrams) (Discussion by A. J. Wiley).

Trans. Am. Soc. C. E., May 5, 1915, vol. 79, pp. 1225

1267. (See also Engineering Record, June 5, 1915, vol.

71, p. 710; Engineering News, Nov. 11, 1915, vol. 74, p.

923; Engineering Record, Nov. 20, 1915, vol. 72, p. 624.) OWYHEE DAM is located on the Owyhee River 21 miles southwest of Nyssa, Oreg., and about 50 miles due west of Boise, Idaho. It was planned for both diversion and storage purposes, and was built under a contract awarded to the General Construction Co. of Seattle, Wash.

OWYHEE DAM

OWYHEE PROJECT, OREGON-IDAHO

BY RUSSELL KIMBALL, ENGINEER, BUREAU OF RECLAMATION

The Owyhee project was authorized by Congress in 1924. Preliminary construction work on the dam was begun in 1928, and the dam was completed in October 1932. The canal system which serves 92,000 acres is now nearing completion. The justification for the project was the relief of a large number of existing irrigation districts, in a high state of cultivation using water pumped from rivers. The construction of Owyhee project permits the use of a cheaper gravity supply and at the same time brings into cultivation additional lands not previously irrigated.

Owyhee Dam raises the water 315 feet above the original river level to the maximum reservoir surface elevation of 2,670. The crest of the dam is 417 feet above the foundation in the river section, and 530 feet above the lowest concrete in the fault zone cut-off, making it the world's tallest at the time it was completed. The dam regulates and controls the Owyhee River waters for diversion through the main canal tunnel no. 1 and the distribution system for the irrigation of land in eastern Oregon and western Idaho, and for supplying supplemental water to 13,690 acres under a Warren Act contract with the Owyhee Ditch Co.

RESERVOIR

Owyhee Reservoir is 52 miles long with a total storage capacity of 1,120,000 acre-feet, including 405,000 acre-feet of dead storage. The drainage area above the reservoir is about 11,000 square miles, of which part lies in Nevada, including the headwaters of the Owyhee River and the South Fork of the Owyhee River. The other parts of the drainage area lie in southwestern Idaho and the southeast corner of Oregon. The reservoir filled for the first time in April 1936.

The average annual run-off is about 900,000 acre-feet. The maximum recorded flow occurred during 1891-92, amounting to 2,300,000 acre-feet. The minimum recorded annual flow was 153,000 acre-feet in 1931. Variations in stream flow of from 100 second-feet to 23,200 second-feet have been recorded.

Most of the reservoir basin including that portion near the dam is in prebasaltic tuff which is practically impervious. The upper end of the basin, where the water is comparatively shallow, is in tight formations of conglomerate, sandstone, shale, and tuff. The portion near the mouth of Dry Creek is in Columbia River basalt, which constitutes the only place where leakage might occur. However, geological opinions indicate that no serious leakage is to be expected.

DAM SITE

The dam site is located at a place where the Owyhee River flows through a box canyon. Test holes show the foundation material to consist of sand, gravel, cobbles, and boulders to a maximum depth of 60 feet, below which rhyolite is found. The rhyolite extends to a depth of 170 to 215 feet below the water surface of the stream and is bedded on pitchstone agglomerate. All the geological and engineering opinions agreed that the foundation rock was suitable for the construction of the dam.

The most serious flaw in the rock is a shattered zone or fault crossing the dam site at about the center of the canyon. This shattered zone was first disclosed by core drilling and later by an open test pit located about 1,450 feet downstream from the dam site, where the fault leaves the canyon. During the foundation excavation, the seam was found to. vary in width from about 12 to 20 feet, and to reach to depths of from 120 to 150 feet below elevation 2,300, all of which zone was removed across the full width of the dam, replaced with concrete and pressure grouted.

THE DAM

Owyhee Dam is a concrete arch-gravity structure, with about three-fourths of the water load carried by arch action* and one-fourth carried by gravity action. The radius of the upstream face at the top is 500 feet and both faces are concentric. The top thickness is 30 feet and the maximum bottom thickness, 265 feet. The upstream face is vertical', for the top 75 feet and below this has a batter of 0.05 to 1. The downstream face is generally on a slope of 0.626 tol. A gravity tangent, 210 feet long, was built at the right abutment. The arch section is 600 feet long at the crest.

Before adopting the arch-gravity type of dam preliminary designs and estimates were prepared for five different types, including a light arch section, an intermediate arch section, a heavy arch section (arch-gravity type), a straight gravity section, and a slightly curved gravity section. In all design studies, uplift pressures were assumed to act over the whole area of the base, varying from full hydrostatic pressure at the upstream face to one-half hydrostatic pressure at the drainage wells; then diminishing uniformly to zero or tailwater pressure at the downstream face.

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Radial contraction joints were provided at 50-foot intervals along the dam. The joints were provided with vertical keyways, 9 inches deep by 3 feet wide, on 3-foot centers. Copper expansion sealing strips, consisting of 20-gage soft copper sheets bent to the shape of a T with double stem, were placed 12 inches from the upstream and downstream faces of the dam, and around all gallery openings. At each 100-foot level a horizontal strip connects the upstream

and downstream copper expansion strips, forming a watertight diaphragm. A system of pipes and fittings was embedded in each joint, for the purpose of grouting after the mass concrete cooled to below the mean annual temperature of 52° F.

All gate installations, drainage wells, the elevator shaft, inspection shafts, and transverse and radial inspection galleries arc accessible through spiral stairway shafts and through 5- by 7-foot circumferential, inclined and horizontal drainage galleries. An entrance adit at elevation 2,377.8 is located in the left abutment, about 200 feet below the dam; and access to the galleries is provided through a 6- by 8-foot tunnel excavated in the foundation rock. The tunnel portal structure is of concrete and is provided with sheet metal doors and a structural steel gate.

The right abutment entrance adit to the dam is located at

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