LAKE ROOSEVELT The Grand Coulee Dam and the Columbia Basin Reclamation Project

CONCRETE

CONCRETE MIXES

The job of greatest magnitude an the Grand Coulee Dam is that of making and placing concrete—20 million tons of it.

To serve various purposes and to suit a variety of conditions, mixes of two classes are used:

Class A, maximum size aggregate 3/4, 1-1/2, or 3-inch depending upon position; water-cement ratio 0.90 by volume; strength 3,000 pounds per square inch at 28 days.

Class B, mass concrete far interior of dam and toe; maximum size of aggregate 6-inch; minimum cement content 1 barrel per cubic yard; maximum water-cement ratio 1.00 by volume; strength 2,800 pounds per square inch at 28 days.

The removal of cofferdams late in 1937 allowed the river to flow through low gaps in the completed foundation

CONCRETE AGGREGATE

Sand and gravel are obtained from a pit furnished by the Government and operated by the contractor, a mile and a half below the dam site on the east side of the river and 800 to 1,000 feet above it.

Pit-run material is delivered by electric shovels, through grizzlies which reject boulders too large to be handled on a belt, to an extensible system of belt conveyors by which material can be transported from any part of the pit to a raw stock pile above the processing plant.

The washed gravel, separated into four size ranges, 6 to 3 inches, 3 to 1-1/2 inches, 1-1/2 to 3/4 inches, and 3/4 to 3/16 inches, and the sand, ranging in particle size from 100-mesh to 3/16 inch, are stored in separate piles below the plant, and moved as required over a 48-inch belt conveyor to stock piles near the east end of the dam 5,965 feet away. The aggregate required at the west side mixing plant was transported across the river on a 36-inch convey or carried, during the constructing of the base of the dam, by a suspension bridge about 4,000 feet long.

The pit contains a large excess of sand, and about 50 percent of the material excavated is rejected. In furnishing aggregate for the contract for the base of the dam, about 3 million yards of sand went to waste. On the completed dam, the excess sand to be handled will exceed 10 million yards.

In columns 50 feet square, the concrete is built up in terraces of 5-foot lifts in movable forms

CEMENT

Cement, purchased by the Government, is shipped in bulk in boxcars from five cement plants in Washington, unloaded through hose and pipe lines by means of cement pumps, stored in 11 steel silos with a total capacity of 55,000 barrels, and blended for uniformity in color and other characteristics before being used. Mixed with air under pressure, it is transported from the blending silos through an 11-inch pipe to the concrete mixing plant 6,200 feet from the blending silos. During the construction of the base of the dam, the cement pipe line crossed the river an a suspension bridge which also carried the belt conveyor supplying sand and gravel to the west mixing plant.

Two and a half miles of cylindrical farms will be required for the 8-1/2-foot outlet tunnels

CONCRETE MIXING PLANTS

Concrete is mixed in two plants, octagonal towerlike structures 44 feet wide and more than 100 feet high, one originally located an each side of the river. At the top of each plant are two bins for cement, one for sand, and one for each of the four sizes of gravel used.

By means of electrically operated devices, under push-button control by one operator, water, cement, sand, and gravel of each size, in quantities appropriate to the mix required, are automatically weighed out for each batch and delivered to one of four 4-yard mixers in each plant, graphic records of all components and the consistency of each batch being automatically recorded.

A hundred and fifty-seven welders. cutters, and helpers were employed at one time on repairs and construction

Two 3,000-foot steel trestles averaging 95 and 175 feet in height were used in placing concrete in the foundation

CONCRETE PLACING

Mixers deliver their charges into 4-yard, bottom-dumping buckets, which are hauled away by 10-ton Diesel-electric locomotives, four to a car on standard-gauge railway tracks on steel trestles. Huge cranes, with a reach of 115 feet or more traveling on the same trestles, remove the buckets from the cars, swing them out over the rising structure, and lower them into the forms, where workmen dump them through specially shaped hopper bottoms and ingenious valves, designed to prevent the segregation of coarse and fine aggregates, and to control the rate of deposition.

As the dam grows, in 5-foot "lifts," placed in any column at intervals of not less than 72 hours, the steel trestles are buried, and forever lost.

The placing of concrete in the Grand Coulee Dam was started in December 1935. Seven hundred thousand cubic yards were placed by June 30, 1936, 2 million yards by April 15, 1937, and more than 4 million yards in less than 2 years. As much as 9,290 cubic yards were placed in 1 day from one mixing plant. The maximum record for a day was 15,844, and for a month, 377,135 yards. With two mixing plants running at full capacity, concrete could be placed at the rate of 1 cubic yard every 5-1/2 seconds.

Closed with massive gates 50 feet square, diversion gaps were filled with concrete after the central section of the base was finished

COOLING

The reaction which takes place between water and cement in concrete always results in the evolution of heat. During a large part of the year relatively warm materials are used in making concrete. The dam must ultimately reach a temperature close to that of the river bed, practically constant throughout the year, and considerably below that of the concrete when placed.

Unless the heat of cement hydration is dissipated as it is liberated, a massive concrete structure will rise in temperature and expand in size over a period of months. As the temperature afterwards falls toward its ultimate value, contraction occurs and shrinkage cracks appear. Structural weakness may be caused, and leakage will result if shrinkage cracks remain unsealed.

In order to prevent damage from expansion and subsequent shrinkage, and in order to permit the final sealing of all contraction joints by grouting before the dam is completed, more than 2,000 miles of 1-inch, thin-wall steel tubing is being set in the concrete, and cooling water is circulated through it. The pipes are set 5 feet apart vertically and 5 feet 9 inches horizontally, and are parallel to the faces of the dam.

The cooling water circulated through the dam will carry away heat in excess of that liberated in burning 30,000 tons of coal. The maximum temperature reached within the dam is 55 to 65 degrees above that of the concrete when placed. The final temperature of the dam will be about 50° F.

Water that flowed placidly into the wide forebay became a raging torrent in the narrow diversion channels

CONSTRUCTION FEATURES

Although the dam will be a monolithic structure, it is constructed in blocks 5 feet thick and varying in area from 50 feet square in the spillway section to 25 by 34 feet at same points in the power-house sections, successive lifts in any column being placed at intervals of not less than 72 hours. Adjacent columns are locked together by a system of vertical keys on the transverse joints and horizontal keys on the longitudinal joints.

Six miles of refrigerating pipe were drive into the toe of a 200,000-yard mass moving clay

GROUTING

After the concrete is cooled and shrunk grout of cement and water is forced into the contraction joints, opened between the columns by the contraction of the concrete, through a pipe distribution system embedded in the concrete as it is being poured, thus forming a solid, monolithic structure. The shrinkage of the concrete, though it opens a crack only three thirty-seconds of an inch wide between adjacent blocks, aggregates about 8 inches in the length of the dam.

A frozen-earth dam 100 feet wide protected a deep bedrock excavation for 7 months from a flood of plastic clay