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hauled to four feeder units and dumped on a grillage of steel beams at ground surface.
Spoil passing through the bars dropped to an apron feeder below, which distributed the irregular supply from the pit at a more uniform rate for the tributary feeders. The feeder belt converged at the hub, which was the control point for the tributary system. A surge hopper and feeder at the hub protected the main conveyor from overloading by smoothing out the surges resulting from several feeder belts. When incoming material began piling up at the surge feeder, all tributary belts were stopped until the overload disappeared.
The main conveyor consisted of approximately 20 conveyor units, varying in length between 156 and 415 feet, depending on the slope. Transfer of material was made directly from the end of one belt to another, the change necessitating a loss in elevation of 6 to 8 feet at each transfer point. The length of the main line was approximately 5,000 feet and the aggregate length of the four tributary lines was 1,500 feet.
The stacker was responsible for the successful operation of the entire system, as it permitted delivery of spoil at the dump without loss of time for changing positions of the discharge end. It consisted of an extensible unit which could be lengthened by adding 50-foot sections; a telescopic unit having a longitudinal travel of 50 feet; and a 175-foot cantilever boom. The three units handled the material in the order named. The boom was pivoted at the loading end and supported at an intermediate point on tractor treads which traveled through an arc of 180°. Both the forward speed of the telescopic unit and the radial movement of the boom were controlled from the operator's station above the tractor.
The conveyor was designed to transport 2,500 cubic yards per hour. The best 7-hour shift record was 17,478 yards and the maximum performance for a three-shift period was 50,700 yards, both amounts representing bank measurement.
The necessity for rapid filling of the cells for the west cofferdam to avoid high water was responsible for abandoning the use of trucks and developing a shuttle conveyor. The excavated material from the cofferdam area was transported by belt conveyor to a hopper located midway of the row of cells and about 200 feet back from the river face. The hopper straddled a track 1,600 feet long, parallel with the cells, which served as a runway for an 870-foot traveling conveyor. The track length permitted an 800-foot travel in either direction with some portion of the belt always under the hopper. Two 200-foot boom arms, supported near the discharge ends on traveling frames, were mounted at each end of the traveling conveyor and discharged the material directly into the cells. Placement of approximately 275,000 cubic yards of cell fill and 125,000 cubic yards of protective embankment at the toe and behind the cells was completed in advance of the 1935 flood season.
AGGREGATE An extensive deposit of aggregate, known as Brett pit, was located on the high mesa east of the river, about 1 miles northeast of the dam site. Explorations showed the deposit to be of glacial origin, 300 feet deep, and covering approximately 70 acres. More than ample supply for the dam and appurtenant works was contained in the pit, in all sizes required for manufacturing concrete. Four sizes of coarse aggregate are used in the mass concrete, ranging from a maximum of 6 inches in diameter to one-quarter
inch in diameter, comprising about 73 percent as compared to 27 percent sand. An excessive amount of fine material results in disposing of approximately half of the volume excavated. Stripping the pit to a depth of 1 to 3 feet has resulted in the removal of over 500,000 cubic yards of overburden.
The location of the pit is 900 feet above the river, a factor which influenced the design and construction of a plant and conveyor system, incorporating the advantages of gravity in the preparation and transportation of the aggregate supply. Two 4-yard electric shovels load directly into hoppers over the ends of the 200-foot boom conveyors which were used to fill the coffer cells. Crawler treads, supporting the boom, move the hopper through an arc of 180°, having a radius of 200 feet. The additional 30-foot swing of the shovel results in a cut 460 feet wide, varying in depth between 40 and 100 feet. Radial flexibility results from mounting the discharge end of the boom conveyor on a track frame, supported by rails along both sides of the end conveyor section. This arrangement for telescopic action, together with the provision for extending the belt line in 50-foot sections, keeps the hopper within loading distance as the shovel advances.
Boulders larger than 16 inches in diameter are rejected by a grillage over the boom hopper, while the balance of the material is discharged on a lateral conveyor line feeding a main 60-inch collecting conveyor belt having a capacity of 2,500 tons per hour. The main line terminates in a trestle from which the raw material is stock piled, to move successively through feeder galleries and vibrating feeders to a 60-inch belt running to a crusher house. Oversize rock is reduced to a 6-inch maximum diameter and combined with the smaller aggregate which bypasses the crusher
and is conveyed to a balancing pile. Two feeder galleries under the toe of the pile serve a belt leading to the screening and washing plant, which is a five-story, steel frame building. Each half of the plant, with identical installations of equipment, is capable of handling the incoming load of 1,250 tons per hour.
The screening and washing operations consist of spraying water from nozzles located over the various screens as the different sizes of aggregate are separated. Sizes less than 74-inch diameter remain as a result of the screening processes by which the coarser aggregates are removed first and dumped into chutes leading to the conveyor room for delivery to the plant stock pile. The fine material and wash water is carried by four steel flumes to the dewatering tanks. The coarse sand settles into compartments and is mechanically raked out and deposited on conveyor belts leading to the sand classifiers, while the balance of the material is sent to the waste dump. The classifiers separate three grades of coarse sand which go to drainage bins for blending. The remaining mixture is returned to the clarifiers where the sludge is removed and the reclaimed water goes to a storage tank. Use of clarifiers results in reclaiming about 85 percent of the 20,000 gallons per minute used in the plant operations. The plant capacity is 1,250 tons of finished aggregate per hour.
A 48-inch conveyor belt transports the aggregates from the plant storage a distance of 4,000 feet to the live storage yard near the east end of the dam. Selection of various aggregates from plant storage is electrically operated by remote control from the live storage yard. Incoming aggregate is unloaded from boom arms extending laterally from an airplane-type tripper which travels on rails between two stock piles. Hinged booms permit elevating or lowering the
lower floor are charged successively by the cone through a retractable chute which charges the mixer through the front opening while in the mixing position. The mixers discharge by tilting downward through an arc of 75° from a mixing position of 15° above horizontal.
discharge ends to reduce breakage of aggregates. Storage yard capacity of 77,000 cubic yards, plus aggregate plant storage of 13,000 cubic yards, is sufficient quantity to provide both mixing plants with a 3-day run. Aggregate from one row of stockpiles is delivered by conveyor belt to storage bins of the east mixing plant, while the west plant was supplied from the other row by a 36-inch belt which crossed the river on a three-tower steel suspension bridge, which also supported a steel pipe conveying east-bound cement under pneumatic pressure to the east mixing plant.
Cement storage is provided by eight 5,000-barrel steel silos in addition to two identical silos for storing the blended cement which is pumped to the mixing plants through steel pipe lines. The pipe line supplying the west plant is 2,000 feet long, and the one crossing the river to the east plant was 6,000 feet long.
Each mixing plant, constructed of structural steel except the reinforced concrete supporting columns and mixing floor, is octagonal in plan, having a diameter of 42 feet and a height of 102 feet. The top of the plant is devoted to aggregate and cement storage space. The floor below the bins is occupied by eight weighing batchers, one for each size of aggregate, two for cement and one for water, the mechanism of which is operated by air pressure and electrically controlled. Ingredients for one mixer are contained in the batchers which discharge simultaneously into a collecting cone. A battery of four 4-yard tilting mixers on the
Two construction trestles, parallel to the axis of the dam, were used to transport the concrete from the plants. The high trestle, at elevation 1,024, is 93 feet downstream, while the trestle at elevation 950 is 328 feet downstream. The trestles will be extended as construction progresses until both are continuous between the east and west plants. When concrete is dispatched to the low trestle a concrete chute connects the mixer with a 4-yard skip which discharges into a hopper for the concrete buckets on cars at the lower level. Concrete for the high trestle is discharged directly from the hopper underneath the mixers into the 4-yard buckets mounted on flat cars. Traveling cranes, with rigid truss arms extending laterally from the trestle, and auxiliary revolving cranes, transfer the bottom-dump buckets of concrete from the cars to the placing areas.
Preparations for depositing concrete in the various blocks of the dam are made by setting forms for a 5-foot lift and installing all items to be embedded in the concrete. The buckets are lowered into place from the trestles and tripped over the point where the batch is to be placed. By means of electric vibrators and spading the concrete is compacted and leveled into layers approximately 1-foot thick, until the
block is carried up to the top of the forms. After 24 hours, v ors in Operation; III-Designing the Belt System; Makconstruction of the next form is begun, and placing of ing Aggregate at Grand Coulee. Engineering Newsconcrete is permitted after an elapse of 72 hours.
Record. Aug. 1, 1935. Government inspectors maintain control over concrete
Preparing Millions of Yards of Aggregate for Grand Coulee production and placing. Aggregates and cements are
Dam. Western Construction News, November 1935. tested individually, in addition to testing numerous samples of concrete taken from the mixers. Samples cured for
Grand Coulee Dam Concreting Plant is Notable for Design various periods are tested in a 200,000-pound compression
Efficiency. Western Construction News, February 1936. machine operated in connection with the testing laboratory Aggregate Production for Grand Coulee Dam. Reclamanear the construction site.
tion Era, June 1936.
Details of Concreting Procedure at Grand Coulee Dam. BIBLIOGRAPHY
Western Construction News, July 1936. Report on Columbia Basin Irrigation Project Engineering
Program for Grand Coulee's Second Cofferdam. EngineerNews-Record, Sept. 24, 1925.
ing News-Record, Oct. 1, 1936. Planning the Columbia Basin Development. Reclamation
Pour 7,000 yards of Concrete Daily at Grand Coulee. Era, July 1927.
Southwest Builder and Contractor, October 23, 1936. Columbia Basin Project Report Shows Feasibility. Recla
Diverting the Columbia at Grand Coulee With Timber mation Era, March 1932.
Cribs and Gravel Fills. Western Construction News, o
December 1936. Preliminary Work Starts on Coulee Dam. Pacific Builder and Engineer, Sept. 2, 1933.
Experiments Aid in Design at Grand Coulee. Civil En
gineering, November 1936. Grand Coulee Dam and Power Plant on Columbia River. Western Construction News, issues of April, May, and
i · Columbia Basin and Grand Coulee Project. Civil EnJune 1934.
gineering, September 1934. World's Largest Construction Conveyor Speeds Excavation
Foundation Conditions for Grand Coulee and Bonneville at Grand Coulee. Western Construction News, March
Projects. Civil Engineering, February 1935. 1935.
· Aggregate Transported Across Columbia by Long SuspenCofferdam, 3,000 Feet Long Built at Grand Coulee. West
sion Belt. Engineering News-Record, Nov. 14, 1935. ern Construction News, June 1935.
Concrete Mixing and Placing. Engineering News-Record, Grand Coulee Project and Dam: Ten Months' Construc
Jan. 23, 1936. tion Progress; Constructing the First Cofferdam: 1– Handles 2,500 Tons per Hour: Wastes 1,000 to 1,500 Tons Planning for Excavation Disposal; II–The Belt Convey of Sand. Rock Products, March 1936.
SALT RIVER PROJECT, ARIZONA
BY LEWIS J. WORKMAN, ASSOCIATE ENGINEER, BUREAU OF RECLAMATION
THE SALT RIVER PROJECT is located in the southcentral part of Arizona in the vicinity of Phoenix. It was one of the first irrigation projects authorized under the Reclamation Act of 1902, and comprises about 250,000 acres of irrigated lands on either side of Salt River. The first problem encountered was the provision of an adequate storage system with a controlled flow in Salt River, for which purpose Roosevelt Dam was constructed in 1906–11. The dam is located in a rugged, mountainous country, east and north of Phoenix, about 63 miles from Mesa and 35 miles from Globe. It is built in a narrow canyon of Salt River, a short distance below the junction with Tonto Creek.
The reservoir occupies the valleys of both streams for a distance of approximately 23 miles. As originally completed, it had a storage capacity of 1,284,000 acre-feet. The capacity was increased 83,000 acre-feet in 1913 by raising the crest of the spillway wier 5 feet. In 1923, piers and gates were installed in the spillway, further increasing the storage capacity by 270,000 acre-feet. In 1936 the spillway crest and gates were lowered about 6 feet to provide additional spillway capacity. After allowing for a reduction of 100,000 acre-feet by silting and the increased capacity provided by the spillway gates, the present storage capacity is 1,420,000 acre-feet, with a reservoir area of 17,500 acres.
The watershed, which covers about 5,760 square miles, varies from desert with a mean annual precipitation of about 8 inches to heavily timbered mountain regions with a precipitation of 35 inches. The flow of the river at the dam site has a wide fluctuation, varying from low flows of a few hundred second-feet to a maximum daily flow, estimated from records below the mouth of the Verde, of 150,000 second-feet, occurring in February 1891.
started. The nearest railroad point, Globe, Ariz., was reached over a rough mountain road. This road was relocated in places and improved so that it served for the transportation of freight until 1905. Another road was built connecting Mesa, Ariz., with the dam site. Mesa had the advantage of being served by two competitive railroad lines, so that better freight rates could be obtained. The Mesa road was about 63 miles long, some 25 miles of it being over a flat desert and the remainder through a rough mountainous region which involved a great deal of difficult location and construction. A total of 112 miles of roads were built, a considerable portion of which became permanent highways. A part of the expense of the Mesa road was borne by the cities of Mesa and Phoenix, Apache Indian labor was used to a great extent on the road construction. All freighting to the dam site was done by horsedrawn equipment.
Due to the high cost, as well as the difficulty of freighting lumber from Globe, a portable sawmill was purchased and located in a heavily timbered region of the Sierra Ancha Mountains, about 30 miles from the dam. Practically all lumber used on the job was sawed by this mill at a substan. tial saving to the project.
Portland cement, if purchased on the open market and hauled to the job, virtually would have prohibited the construction of a masonry dam, due to excessive cost. An excellent supply of dolomitic limestone and clay near the damsite made logical the purchase of a cement mill and its erection at the job. Fuel for burning the clinker presented the greatest problem, but this was solved by using oil shipped from California. During its operation, the mill produced the cement used in the dam as well as in other structures of the project, the total output being about 338,000 barrels. A temporary steam plant of 150 horsepower capacity was installed on the job, to furnish electrical power until a power canal could be constructed and a temporary hydroelectric unit put in service.
Due to the scarcity of a good grade of sand near the dam it was decided to install a sand crushing plant. The dolomitic limestone produced too harsh a product, so sandstone was crushed with it, a mixture of half limestone and half sandstone giving the best results. About 87,000 cubic yards of sand were produced by the crushing plant in its 4 years
The contract for the construction of the dam was awarded to John M. O'Rourke & Co., of Galveston, Tex., in April 1905. Owing to the fact that the dam site was located in a mountain region, practically inaccessible for moving supplies, a large amount of preliminary work was necessary by Government forces before actual construction could be