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batchers, each with a capacity of about 5,000 pounds. Sand and gravel batchers were installed directiy beneath their respective storage bins which extended back from the mixers toward the canyon wall. The materials dropped directly into the weighing batchers and discharged from the batchers on to a belt conveying the aggregate to a split chute, which directed the flow to either of two mixer charging hoppers by means of a flop-gate. The cobble batcher was filled by a short apron conveyor and discharged at approximately the same time as the other aggregate batchers, directly into the split chute.

The operating floor was located just above the four mixers and approximately level with the top of the mixercharging hoppers. Cement batchers were located directly over these hoppers and discharged into the hoppers at the same time that the aggregate in the hopper was released into the mixer. Water was weighed in a batcher supplying two mixers.

The controls for all batching and mixing operations were located on the operating floor and were so arranged that one operator could handle two mixers, or two operators the entire plant. Aggregate, cement, and water batchers all refilled automatically to a definite weight immediately after discharging. By pressing a single button on the operating floor, all five aggregate batchers were discharged and the materials brought together in the mixer-charging hopper.

Each batch in the mixer was automatically timed to mix 2% minutes, after which the dumping mechanism was automatically unlocked for tilting to discharge into buckets for transportation to the point of placement.

All batchers were equipped with scale dials which made observation of the batching operations possible. The scale dials for the four sand and gravel batchers were arranged in a group in front of a set of air valves which provided manual control for the batchers. The scale dials for the cobble, water, and cement batchers were arranged on the operating deck facing the mixer operator.

Graphic recorders also were provided with each set of batchers. These recorders were located on the operating deck in full view of the operator and provided a line graph of the operations of each batcher in the set and a consistency graph for each mixer. The charts made by the graphic recorders were removed after each shift and became the property of the Bureau of Reclamation as a record of the plant operation.

The plant was capable of producing about 17 batches of concrete per hour for each mixer or a total of about 280 cubic yards per hour for the entire plant.

The high-level mixing plant was located on the Nevada side of the canyon, a few hundred feet from the rim and about 1,000 feet downstream from the dam. As regards the type of equipment and the general methods of handling materials, this plant was much like the low-level plant.

One notable difference was that the aggregate storage bins and batchers were built in a separate section and the material was transported to the mixer charging hoppers by long sloping conveyors. Another change was that four circular steel cement silos were constructed directly over the four primary mixing units.

When first put in operation, only the two central batching and mixing units were installed. From this stage the capacity of the plant was increased by adding the two remaining mixers and batching equipment. Two mixers from the low-level plant also were added to the regular set of four mixers making a total of six mixers under operation at the high-level plant. This plant produced almost half of the concrete for the dam, all of the concrete for the power-house and valve houses, and most of the concrete for the spillways, intake towers, and penstock system.

The aggregate storage bins were designed on the same general principles as those at the low-level plant. Five bins for the five sizes of aggregate, each extending the full width of the bin section and supplying four batchers, were provided. A railroad track was carried on top of the bins and the cars of material were dumped from the track directly into the bins.

The batching scheme was almost identical with that of the other plant, each batcher being located directly beneath a slide gate in the bottom of the bin. Material from the batchers was discharged by pushing a button at the control stand on the operating deck, and was carried by a conveyor belt running beneath the batchers to the mixer charging hopper at a 45-foot lower elevation.

The charging of the mixers and the mixing was, in general, in line with the operations described for the low-level mixing plant. The four primary mixers discharged into loading hoppers arranged with two interchangeable spouts which could be moved into operating position to load one of several types of conveyance. The automatic system, dial system, and graphic recorders were essentially the same as used in the lower plant.

Water for the concrete mixing operations was obtained from the river. Analyses showed that the ordinary river water was satisfactory, except for the silt-content which was frequently heavy. The water for the low-level mixing plant was pumped from the river several hundred feet upstream from the plant, to a 50-foot diameter traction clarifier where all silt in excess of 500 parts per million was removed. After this treatment, the water flowed by gravity to a 125,000-gallon storage tank, situated adjacent to and higher than the mixing plant.

The water for the high-level plant was obtained by pumping from a sump in the river bed gravel near the lower cofferdam. This water was clear and no clarifying was required.

Concrete from the low-level mixing plant was hauled to the point of delivery over a standard gage, double track railroad by electric locomotives equipped for both battery and third-rail operation. The railroad was carried along the Nevada side of the canyon, at elevation 720, and was extended along the abutment of the dam by a steel bent trestle which reached as far as the downstream toe of the dam.

Concrete from the mixers was emptied directly into 8cubic yard buckets, loaded on specially built ffat-cars provided with four openings for the buckets. Each car carried two loaded buckets from the mixing plant to the point of delivery where two empty buckets were received and the two loaded buckets removed.

After the concrete in the dam had reached such a height that the use of the trestle at elevation 720 became impracticable, a large stiff-leg derrick was provided to remove the buckets from the railroad at the upstream face of the dam and transfer the buckets for delivery to the point of placement.

When storage was commenced in the reservoir, the lowlevel mixing plant and railroad were abandoned and the high-level plant was used.

A railroad along the rim of the canyon between the mixing plant and the Nevada spillway was provided for the transportation of concrete from the high-level mixing plant. The operation of the railroad was similar in detail to the low-level method of procedure. Considerable use of trucks was also made to haul concrete from the plant to the various parts of the job.

A system of five cableways, spanning the canyon, was provided by the contractor to handle concrete and other materials. All five cableways were designed for normal operation with 20-ton loads and infrequent loadings up to a maximum of 40 tons. The two longest units required a span of 2,575 feet to cover the two spillways. These cableways were identical units with head and tail towers traveling on parallel tracks 800 feet long, the towers being 90 feet high to provide clearance over the intake towers.

Two cableways, operating on concentric radial tracks, were provided for the downstream portion of the dam and central portion of the powerhouse. The span for these cableways was 1,405 feet. Each head tower was 75 feet in height, and each tail tower 42 feet in height. A radialtraveling type cableway, with the head tower fixed and the tail tower movable throughout a spanning radius of 1,374 feet and an arc of approximately 600 feet was provided to cover most of the powerhouse area.

COSTS

Payments were made to Six Companies, Inc., the principal labor contractor, under the schedule of the original specifications, 18 orders for changes and 39 extra work orders. The separate items for payment numbered nearly 600, of which a few are given in the following tabulation:

NaIure of work

Stripping canyon walls

Excavation: All classes, in diversion tunnels.

Excavation, common, for foundation of

dam, powerhouse, and cofferdams. Excavation, rock, for foundation of dam. Excavation, all classes, for spillways in open cut.

Excavation, all classes, for intake towers.

Excavation, all classes, in penstock tunnels, outlet tunnels, and power penstocks.

Rock barrier below downstream cofferdam.

Earth fill in upstream cofferdam

Drilling grout holes in tunnels, adits, and shafts.

Drilling grout boles in foundations for dam and spillway crests more than 100 feet and not more than 150 feet deep.

Pressure grouting in tunnels, adits, and shafts.

Grouting contraction joints in dam

Concrete in linings of diversion tunnels.

Concrete in dam

Concrete in spillway structures

Concrete in intake towers

Concrete in dome roofs of intake towers

Concrete in bridges to intake towers

Blending cement

Installing standard steel pipe

Installing structural steel

Installing metal conduit larger than 1

inch diameter and not larger than 2H

inches diameter. Transporting penstock pipe and tools..

Installing cylinder gates

Installing drum gates

Installing bulkhead gates

Construction and operation of cooling

plant.

Placing powerhouse roof

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i Variable. t Lump sum and cost plus 15 percent.

BIBLIOGRAPHY

Boulder Dam Today. (Two articles.) Engineering NewsRecord, Feb. 6, 1930.

Construction of the Boulder Dam. Compressed Air Magazine, series of articles beginning November 1931 and continuing to completion of the dam.

Construction Features at Boulder Dam. (Series of articles.) Reclamation Era, April, May, July, August, September, 1932; March, April, May, 1933.

Classification of Concrete Aggregates for Boulder Dam. Pit and Quarry, Oct. 19, 1932.

Boulder Dam Cement Specifications Tentatively Formulated. Engineering News-Record, Nov. 10, 1932.

First Stage at Boulder Dam. (Special issue.) Engineering News-Record, Dec. 15, 1932.

Mass Concrete Research for Boulder Dam. Journal, American Concrete Institute, March-April 1933.

Hydraulic Model Tests for Boulder Dam Spillways. Engineering News-Record, Aug. 10, 1932.

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GRAND COULEE DAM

COLUMBIA BASIN PROJECT, WASHINGTON

BY C. H. CARTER, ASSOCIATE ENGINEER, BUREAU OF RECLAMATION

THE COLUMBIA BASIN PROJECT, embracing a large area in eastern Washington, has progressed through successive stages of investigation to the construction of the first and principal feature, Grand Coulee Dam. Situated on the Columbia River about 90 miles west of Spokane, the construction site has been the scene of intense activity since excavation work began in December 1933.

The project, as planned, ultimately will irrigate about 1,200,000 acres in the Big Bend of the Columbia River, extending as far south as its confluence with the Snake River. Various proposals of development have been combined into a comprehensive plan which will provide the essential construction features for ultimate development.

The ultimate project combines irrigation with power development by constructing a high dam across the Columbia River, creating a reservoir from which the irrigation supply will be pumped into the Grand Coulee regulating reservoir and conveyed by gravity canals to the project lands. The power plant, with an installation of 18 main generating units having a total capacity of 1,890,000 kilowatts, will produce 8,100,000,000 kilowatt-hours annually of firm continuous electrical energy, in addition to a considerable amount of secondary energy, part of which will be used to meet pumping requirements. Conserving the river flow and applying it to dry lands which at present cannot be cultivated profitably, will produce crops and create homes for tens of thousands of families.

RESERVOIR

The headwaters of the Columbia River originate in Columbia Lake of the Canadian Rockies and are augmented by the principal supply from the western slope of the Rocky Mountains and from the Selkirk and Bitterroot Mountains. The drainage area of 74,000 square miles is roughly triangular in shape and includes heavily timbered, mountainous regions in parts of British Columbia, Idaho, Montana, and Washington. Deep snow at high altitudes and numerous large natural lakes near the headwaters serve to regulate the stream flow by retarding flood peaks and supplying the heavy run-off for maximum irrigation requirements during the summer months.

As a potential source of power development the Columbia

ranks first among our rivers. It produces the second largest run-off in the United States. The river has a total drop of 1,300 feet between the International Boundary and the Pacific Ocean. The territory surrounding the dam site is generally rugged in topography, increasing in roughness to precipitous slopes and ledges adjacent to the river channel. The unusual difference in elevation between the stream bed and lands which are susceptible of irrigation, constitutes the principal problem in the diversion of water.

The river discharge during the period of record at Grand Coulee, from 1913 to 1935, varied from 17,000 to 492,000 second-feet, amounting to an average annual run-off of 80,000,000 acre-feet. The reservoir impounded by the dam will have a maximum capacity of 9,645,000 acre-feet and will extend 150 miles upstream to the International Boundary. The lake will have a surface area of 82,000 acres when filled and will supply 5,200,000 acre-feet of storage by being drawn down a maximum of 80 feet during seasons of low run-off. The annual diversion requirements for the project are estimated at 5,300,000 acre-feet, or approximately one-tenth the minimum annual run-off of 53,200,000 acre-feet.

GEOLOGY

Bedrock at the dam site is generally uniform in elevation, and bears only slight evidence of deterioration from weathering, except isolated areas where the condition of the rock necessitated excavation to depths of from 5 to 20 feet. Surface irregularities consist of eroded grooves and channels and three pronounced depressions over the foundation area, one being a minor fault zone near the right abutment. The river bed is approximately 3,000 feet wide between the rock abutments which arise from the canyon floor on about and 1:1 slopes, respectively, at the right and left canyon walls. The river bends sharply from a westerly to a northerly course, just upstream from the dam site.

Field tests to determine the depth of overburden and quality of bedrock were begun in 1921. Fourteen diamond drill holes were put down at that time and additional holes were drilled in 1930. In 1933 a more extensive drilling program was begun, to obtain samples representative of the entire foundation area. The explorations included a series of vertical and inclined borings into bedrock, test shafts and

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