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Boulder Dam - 1937

May 31, 2021
Narrator: For countless centuries, the murky waters of the Colorado River wound their way through the towering canyons of its 1,700-mile course, traversing the arid southwest, much of it little known except to native Indians and the few bands of intrepid explorers. Draining a vast mountainous and desert region, entering seven of the largest western states, it poured its waters southward into the Gulf of California, carrying to its delta an enormous volume of silt and periodically flooding the prosperous cities and rich agricultural districts. close to its mouth. with devastating floods. From the time of its discovery, it remained a challenge to engineers who attempted to control it until the enactment in 1928 of the Boulder Canyon Project Act, which authorized the construction of the Boulder Dam.
boulder dam   1937
In Black Canyon, where the Colorado River forms the boundary between Nevada and Arizona, in the very heart of the great desert of the Southwest, the United States Department of the Interior, through its Bureau of Reclamation, was ordered to proceed with construction of this the most powerful of the dams. Roads were built through the desert, railroad lines cut their steel ribbons through sagebrush and cacti, and transmission lines for power construction stretched hundreds of miles across the heat-stricken wastelands of the southern desert. Snowfall. All sectors of the country were asked to contribute to the staggering quantity and wide diversity of materials needed: thousands of tons of steel; millions of barrels of cement, machinery, gasoline and oil by thousands of gallons; tools; construction materials: all this and much more was concentrated at the site of operations in an endless flow.
boulder dam   1937

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boulder dam 1937...

The engineering forces completed their studies, working in the most dangerous conditions, and each state of the Union provided its quota of workers and craftsmen. In what had once been an uninhabited, waterless desert supporting only a sparse, hospitable growth of chaparral and cacti, the beautiful little town of Boulder City was built in the short space of fifteen months to house the 5,000-man army. that were going to be used. There was no construction camp here like that known in the early days of the West. Instead, Boulder City was developed as a model city, providing all the facilities and amenities to its inhabitants.
boulder dam   1937
Four churches, a fully equipped modern school, and several civic organizations provided for the community's cultural needs, while a theater and several clubs provided recreation. A thriving commercial section developed along the main streets, while pleasant houses surrounded by gardens faced the wide, tree-lined residential avenues of this modern and impeccable city. The buildings that housed the offices of the Bureau of Reclamation and the civic administration, which reported directly to the federal government, were located in the middle of pleasant parks that were welcome havens of rest after the daily work in a country where the summer temperature often reaches 125 degrees above zero.
boulder dam   1937
In the commercial area of ​​the city, the arcades formed a protection against the tropical sun. Gorgeous flower gardens bloomed in stark contrast to the surrounding desert. Street after street, the white huts of married workers were reminiscent of the military camps of 1918, while single men were housed in air-conditioned dormitories, each accommodating 176 occupants. In the sanitary and electrically equipped kitchens, tons of food were prepared and served daily in conditions that would have met with the unconditional approval of any modern housewife. A corps of cooks and waiters could feed up to 1,300 men at one table. The menus were varied and the food was of excellent quality.
Since Boulder City was about seven miles away from the dam site, it was necessary to provide transportation for workers to and from work. This was achieved by a fleet of passenger trucks, some of which carried up to 160 men. A twenty-four-hour day was divided into three shifts of eight hours each for all types of work. July 4, Labor Day and Christmas were the only holidays observed once the rapid pace of the ambitious construction schedule was set and underway toward the milestone of an achievement unprecedented in the history of American engineering. It was in March 1931 that Six Companies, Incorporated of San Francisco, California was awarded the general contract for the construction of the project, including the Boulder Dam and its adjoining works, and by early summer of the same year, preliminary construction work was in progress. full swing. in the Black Canyon.
During this early period of construction, before roads were built deep in the gorge, man and materials were forced to embark or travel along the walkways, often strung between the sheer walls of the canyon at dizzying heights above the waters. muddy river The most dangerous river in the world. It wasn't long before roads and rail lines penetrated to the lower reaches of the canyon. To provide these transportation arteries, thousands of tons of virgin rock were quarried from the ancient gorge walls. Thus the first thunderclaps of man's determination to conquer the Colorado River reverberated among the sheer cliffs of the canyon, which until then had known only the warm silence of the desert and the roar of the river's furious floods.
The drilling of four diversion tunnels to carry the stream around the dam site during construction, two on each side of the river, fifty-six feet in diameter and averaging 4,000 feet in length, constituted the first major operation of construction. The drilling jumbos used on this work were mounted on motor trucks for ease of handling and were capable of drilling twenty-four to thirty gunpowder holes on the course simultaneously using boring drills. The tunnels were excavated through the rock simultaneously from four directions: one at each end and two drilling in opposite directions from an auxiliary tunnel at river level located approximately halfway into the main borehole.
A pioneer hole was drilled on the top line, followed closely by excavation to complete the fifty-six foot hole. Thousands of tonnes of drilled steel were used in this work and the sharpening workshops were kept working at maximum speed day and night to maintain a constant supply. After drilling the gunpowder holes and blasting the rock, electric shovels and trucks entered the tunnels in order to remove the shattered material. A non-stop parade of heavy trucks, each carrying eight to ten tons of rock, moved along the steep paths carved into the canyon walls to dispose of the material in the ravines adjacent to the dam site.
This phase of the task, which involved excavating and handling more than one and a half million cubic yards of material, was completed over a period of thirteen months and was considered the most grueling part of the job for both men and crew. machinery. Once the tunnels were excavated, they were lined with concrete one meter thick. Due to the unprecedented size of the holes, special equipment was designed to facilitate this task. The tunnels were lined in segmental sections, with the inversion or base being the first in which the concrete was placed. A gantry crane operating through the tunnel itself handled the concrete throughout this operation.
The side walls were then covered with movable steel formwork, which moved across the excavated section on rails placed from portal to portal. The upper arch was placed with the use of a concrete gun powered by compressed air. To prepare the canyon walls to receive the dam's abutments and remove loose, dangerous rock from the surface of the cliffs that overlooked the site, many tons of rock were torn up and hurled into the depths of the canyon in a series of spectacular explosions. which occurred almost daily during the period between the start of operations at the dam site and the time actual construction of the dam began, approximately two years later.
To reach their positions on the canyon walls, the men engaged in the work of drilling and handling explosives for these enormous explosions traveled in cages or containers, suspended from cables, at heights of hundreds of feet above the river. To the casual observer, this dizzying ride through the sky must have seemed truly exciting, but for the workers themselves it became second nature and part of the day's work. The first step in preparing for the explosion was to drill gunpowder holes in the rock of the canyon wall. For this, the hammer drill, operated by a single man, was generally used.
The holes were then loaded with dynamite and the explosion occurred, breaking the air with its detonation and shaking the very earth with its force. After the explosion, acrobatic workers, known in construction camp parlance as high-altitude climbers, swarmed over... ... fragments of rock shattered and dislodged by the churn of the explosion. Only in this way could the debris from the walls be successfully cleaned. Swinging in bosun chairs from the edge of the canyon, these daredevils were protected in their dangerous work by hard helmets, safety ropes and other safety devices. …preparations were made to divert the river through the tunnels.
A small explosion breached a temporary dam... ... controlled at the entrance to one of the tubes, opening the way for the free passage of water into the fifty-foot concrete-lined hole. A temporary earth and rock dam was quickly placed across the creek, diverting the entire flow. Within twenty-four hours, the Colorado River, under control for the first time in its history, was flowing around and beyond the dam site through massive diversion pipes. A historical record was established by placing the more than one million cubic yards of material necessary for the construction of the two cofferdams, barriers in themselves of no mean proportions.
The earth fills were compacted to a height well above the high water mark to prevent river flow from entering the operations site during construction of the dam and power plant. Once the cofferdams were completed, the site was left without water and the fleet of electric shovels and trucks went to work excavating material from the river bed to provide the foundations for the structures. This excavation was carried out to a point 135 feet below the old river level, requiring the handling of more than two million yards of rock, soil, and sand. Here, too, the endurance of both man and machinery was tested in transporting waste from the lower depths of the gorge.
As cleanup of the dam site progressed, the former bed of the Colorado River was exposed. Here geologists could read the story of what had happened years before, when the chasm now called Black Canyon had been carved out of the primeval rock by the rushing water of a great inland sea and the Colorado River was settling into its present bed. . To ensure the greatest possible stability to the dam's foundations, meticulous care was taken in preparing the rock surfaces to receive the first concrete. The sand and gravel for the four and a half million cubic yards of concrete necessary for the construction of the dam and its adjoining works were obtained from a detrital deposit located on the Arizona side of the River, about twelve miles upstream from the site of The prey.
Here the raw material was excavated by dragline and transported by train to the gravel screening and washing plant, which was the largest of its kind ever built, being capable of producing 20,000 tons of crushed, screened, classified and washed materials every twenty-four hours. . Upon arrival at the plant, the raw material was poured into hoppers, from where it was transported to the plant through endless belts. Here it went through the various stages of screening, by which it was converted into aggregate material suitable for the manufacture of concrete of a quality that met the most rigidly uniform requirements. Oversize pavers, meaning those measuring more than nine inches in one dimension, were first sorted, then crushed and returned to the plant for regrading along with the raw material.
The screening plant itself consisted of four towers of similar design, each equipped with a screening apparatus and each separating gravel of different sizes from the mass of raw material arriving at the unit via conveyor belts. An endless stream of raw gravel from the pit passed over the screens and the selected material was transported to the stockpiles via conveyor belts, each of the four sizes was stored separately, ready to have on hand when needed in mixing plants. A clarifier tankIt provided six million gallons of clean water daily to wash gravel and sand. The raw material for making concrete, which was classified as sand, was classified for the second time into three sizes after discarding very fine and undesirable sand.
The three selected sands were then recombined into a uniform mixture to meet the specifications of the concrete to be used in the project's dam and attached structures. The sand was then stored pending construction program requirements. As sorted materials were needed, conveyor belts loaded the sand and gravel onto rail cars for transport to concrete mixing plants located at the dam site, several miles away. The concrete was mixed in two plants: one located on the canyon floor upstream of the dam and the other on the canyon rim on the Nevada side immediately above the dam site, both equipped with the most advanced machinery for mixing. concrete manufacturing.
Upon arrival at the concrete mixing plant, sand and gravel of different sizes were stored in separate containers. A sizable railway system was required to maintain a constant flow of material from the gravel pit to the screening plant and from the screening plant to the concrete mixing plants. Bulk cement was unloaded from the railway cars using a pneumatic pump and transported to the mixing plant containers where cements from various production sources and different physical and chemical characteristics were combined into a uniform product. This was necessary due to the requirement for standardization in workability, strength, texture, color and other properties of concrete.
Following the progress of concrete manufacturing through its successive stages, we see the various ingredients entering the concrete mixing plant where they were combined scientifically and under strict inspection to obtain a finished product. With a maximum capacity of twenty-four cubic yards of concrete every three and a half minutes, the high-level mixing plant at Boulder Dam represented the ultimate plant facility of its kind. Here the automatic equipment not only controlled the dosage of concrete ingredients, but also maintained a graphic record of each plant operation. From his position on the mixing plant control platform, an operator could direct the entire mixing cycle, from the initial weighing of ingredients through the entire mixing process.
The human element was almost completely eliminated as the mechanical equipment was capable of automatically selecting, measuring, weighing and recording the appropriate materials in the precise quantities required for the production of a given mixture, to which the parameters had previously been adjusted and configured. recording dials. . Here we also found the production line conveyor belt that speeds up the process by carrying components from the measuring and weighing hoppers to the dosing containers, from where the materials were poured into four cubic yard capacity rotary mixers. Water was added in controlled quantities and the entire mass was thoroughly stirred as the last step in the economical and efficient manufacture of a concrete strong enough to withstand the enormous pressure to which the dam would be subjected.
Concrete was shipped from the mixing plant to all sections of the site and, due to the different conditions, different types of containers and transportation methods were needed. Electric trucks and trains were used as transport vehicles and containers ranged from eight cubic yard capacity bottom dump buckets to four cubic yard capacity transit mixers. The latter were used on long journeys when it was necessary to agitate the concrete during transport to avoid segregation of the mixture. However, most of the concrete handled on the project was transported in eight-cubic-yard buckets and transported from the mixing plants by electric train.
A system of nine aerial cable cars, spanning the canyon from edge to edge and anchored at each end to mobile towers, was used to transport concrete and other materials from train or truck delivery points to the dam and other project structures. . It was on June 6, 1933 when the first concrete cube was placed in the lowest part of the dam, 135 feet below the level through which the undisputed Colorado River had flowed a few months earlier. What would become the highest dam in the world began to rise from the impregnable rock of its foundations. As bucket after bucket of concrete was poured into the forms, the plan of the structure became evident and soon extended along its entire 660-foot-thick dimension at the base.
On the lower levels of the structure, concrete was placed from a trestle anchored to the snowy canyon wall. The concrete was poured in keyed or interlocking columns, the design of which became more noticeable as the five-foot layers, or risers, in which the concrete was placed rose from one level to the next. As placement work progressed, crews became adept at handling the equipment and unprecedented daily pours were achieved, which were surpassed by later achievements on this same structure. Transit concrete mixers were transported on trucks from whose platforms they could be removed and handled by cable cars. These were used to place concrete in the confined forms along the abutments, where the eight cubic yard cubes could not be handled.
Randomly selecting a bucket among the hundreds of thousands that traveled from the canyon rim via the cable cars to the dam forms, we see the typical operation, from the moment the bucket is picked up on the cable car at the rim of the cannon, balanced in the air over the gorge hundreds of feet above the forms, its tremendous weight of twenty-two tons moving easily and elegantly over the cable while being lowered into the forms with an ease and certainty seemingly out of proportion to its great volume and tonnage. . As the cube descends, suspended at the end of hundreds of feet of cable strands, it is received into the forms.
The safety locks were opened, the signal was given, and eight more cubic yards of concrete were added to the mass of the dam. The concrete was compacted into the forms by mechanical vibrations, the application of which ensured dense compression against adjacent surfaces. Workers were transported from the canyon rim to the dam forms via an inclined skid, or monkey slide as it was called, that operated across the Nevada Pillar excavation. The Boulder Dam workers represented a cross-section of the American working class, and many remained on the job throughout the construction period. With an ambitious schedule of progress to meet, and with work continuing in all conditions and in all seasons of the year without ceasing, rain or shine, day or night, in one year minus four days, two million of the three and a quarter million cubic yards of the total volume of the dam had been placed in the formwork.
And the Boulder Dam had reached an impressive height, already taking its place as one of the wonders of the West and a major tourist attraction. Meanwhile, progress had been made in the construction of the structures attached to the dam itself. Construction of the power station, a U-shaped structure situated at the foot of the downstream dam, had been underway for some months, and as its substructures took shape, they gave a glimpse of the beauty it would later possess. . The intake towers, two on each side of the canyon wall immediately above the dam, were under construction and arose from a labyrinth of reinforcing steel that rose rapidly toward the upper rim of the canyon.
These structures would later serve as giant inlet valves for power outlet conduits and penstock systems. And placing the seats for the gigantic cylindrical doors was an important phase in its construction. Located at the maximum water storage level of the reservoir, the two spillways, designed to act as overflow controls on the open diversion system, were located one on each side of the river upstream of the dam and within the reservoir area. Construction work progressed simultaneously with that of the dam itself. One of the most interesting and spectacular phases of the work was the fabrication and installation of the enormous steel penstocks that form the conduits for the power and pressure output systems.
This work was done by the Babcock & Wilcox Company of New York City, who erected a modern steel mill near the dam site to facilitate the task. As the pipe units to be manufactured were of unprecedented size and weight, it was necessary to design, build and install special machinery solely for this task. Measurements were made to fabricate pipes with diameters between eight and one-half and thirty feet from steel plates varying in thickness from five-eighths of an inch to two and three-quarters of an inch. As it was impossible to ship units of this size across the country by rail, steel plates were brought in from rolling mills in the east and the entire manufacturing process, including rolling and assembly, was started and completed at the Boulder Dam plant.
The first step in the manufacturing process, once the plates had been arranged to dimensions, was to shape the edges to ensure precision and accuracy in subsequent manufacturing steps. This work was carried out on a planing machine capable of handling a fifteen meter long strip of steel. The plates were then given an initial bend in a giant press operating at a pressure of 3,000 tons. This initial bending was necessary to avoid damaging the rolls when the plates in the next manufacturing step were rolled into a circular shape. The plates, which go into the manufacture of thirty-foot diameter penstock pipe, were manufactured through the initial manufacturing steps in widths of eleven feet.
These plates were two and three-quarter inches thick and were rolled into a circular shape by passing them through forty-inch vertical rollers until the desired degree of curvature was obtained. One of those plates represented a segment equal to one-third of the entire circumference of a finished pipe. After being rolled to the correct degree of curvature, the three curved plates were joined together to form a single ring ten meters in diameter and three meters long. Two of these rings were then joined together, end to end, to form a workshop unit eight meters long. All joints were made by electric welding and to form the longitudinal joints an automatic welding machine was used, which moved on a chassis supported in line over the joint.
As these piping units were of a size never before assembled, it became necessary to design and build special machinery to perform many phases of the work. This was especially true in the manufacture of mitered rings which were then assembled into curved sections. The general use of electrical cutting and welding was applied not only to pipe sections but also to the manufacture of other fabricated units. A complete workshop unit weighed between 150 and 184 tons, depending on its design determined by its end use when installed in the penstock system. The circumferential joints were made by rotating the rings, forming a workshop unit under an electric welding machine suspended above the line of the joint to be welded.
Each foot of welded joint was subjected to careful x-ray examination and recorded on photographic film that exposed even the slightest imperfections in the continuity of the weld. Samples of typically welded joints were subjected to rigorous laboratory tests calculated to produce a deformation condition far superior to that which the joint would withstand in actual use. The discovery of the slightest imperfection was reason enough to reject an entire unit. In stark contrast to the meticulous care and precision exercised in every phase of its manufacturing was the actual size and weight of the tubing unit. Specially designed heavy rigging was required to move the sections through the workshop and high-capacity cranes to move them step by step through the progressive phases of their fabrication.
To equalize the tremendous internal stresses introduced into the plates by bending and the additional temperature stresses incurred during welding, individual pipe sections were subjected to a temperature of 1,400 degrees Fahrenheit in a gigantic annealing oven. This temperature was not induced by the application of the flame itself but by the circulation of superheated gas. The workshop processes were carried out only until the production of the unit section. As these sections were to be joined together to form a continuous penstock, measures were taken to precisely achieve this joining in the tunnels. To ensure a field meetingSatisfactorily fitted, the ends of the sections were machined on a gigantic vertical lathe operating along the ten meter diameter of the pipe.
After a final inspection, the pipe section was ready for installation. A modern, streamlined train passing through one of the enormous tubes offers an interesting route for the comparative size of the unit. The job of transporting the pipe section from the plant to the dam site was in itself a huge task, and to carry out this job a special trailer with the capacity to transport 200 tons was designed and built. Caterpillar tractors provided the motive power, as the trailer itself was not equipped with means of locomotion. During handling, confirmation of the pipe section was maintained by rigid internal reinforcements.
The movement of heavy trucks was controlled by air brakes and power steering devices with which the trailer itself was equipped. Upon reaching the edge of the canyon, directly above the dam site, the unit was maneuvered into position to descend into the canyon. To accomplish this task and handle other heavy equipment, a permanent cable car of 200-ton capacity had been strung over the gorge, its six three-and-a-half-inch track cables firmly anchored in the rock of the canyon wall. The cable car was operated from a control tower that overlooked the canyon, from where the operator had a complete view of all its movements.
The heavy lifting machinery controlled by synchronized motors was the largest and most powerful of its kind ever built, as were the track cables themselves that crossed the canyon at a distance of 1,256 feet at a height of 700 feet above the river from the main tower located on the Nevada side. … …cables ran through the car, which touched the lifting and translation cables. To lower the enormous tubes to the lower levels of the canyon, a specially designed heavy-duty platform was used, which the workers knew as the moonbeam due to its peculiar shape and from which the sections of pipe were suspended, while they were held with a heavy steel cable sling.
After all tie-downs were secured, the pipe section was lifted from the trailer to begin its slow, carefully controlled movement above the cable car traveling from the edge into space, suspended 700 feet above its final position. When the cable car, with this tremendous weight of steel, was maneuvered into place above the intended location far below, the lifting cables were slowly released and the pipe was lowered under absolute control into the canyon. Here, a second specially designed car waited at the access tunnel portal to relieve the load on the cable car and carry the section of pipe underground to become part of the extensive conduit system that penetrates the cliffs on both sides of the canyon.
With workers working in the deep underground tunnels, the mammoth task of placing the penstocks into position to form continuous conduits between the entrance towers and the power station and exit works was achieved. The separate units were moved into place with the help of cables and once in position were joined together with pressure pins to form a continuous pipe. While work was underway on features attached to the Boulder Canyon project, an uninterrupted flow of concrete had been pouring into the dam forms from both mixing plants. Progress was limited only by the limitations of good engineering and construction practices.
Day after day, week after week, the top of the structure approached its maximum height of 730 feet, far above the top of any other dam built by man or likely to be built in the years to come. The schedules established at the beginning of the work fell far behind as the dam's concrete narrowed toward its summit and the structure widened between its abutments, approaching the upper edges of the canyon walls. In June 1935, the dam structure was completed, two and a half years earlier than originally planned. In September of the same year, President Franklin Delano Roosevelt, praising both the designers and the builders, dedicated Boulder Dam to the nation's progress.
When the final construction works were completed, the impressive beauty of the structure became evident. The highway traversing its 1,300-foot ridge forms a magnificent link in a transcontinental highway. The reservoir that fills behind the dam was named Lake Mead in memory of Dr. Elwood Mead, the late Reclamation Commissioner, whose work culminated in the construction of the Boulder Dam. The largest man-made body of water in the world, it extends upstream 115 miles and into the lower reaches of the Grand Canyon with a 550-mile shoreline that opens to views unseen by man until invaded by gradually rising waters. of the reservoir.
Equipped with cylindrical gates that function like giant valves, the four intake towers serve as inlets to the four steel gates that supply water to the turbines and outlet valves. Perched on shelves carved into the canyon walls, they rise 403 feet to a height above the dam crest and canyon rim. With a combined capacity of 400,000 cubic feet of water per second, the two spillways, located one on each side of the canyon upstream of the dam, will serve as high-level controls once the reservoir water has reached its maximum storage elevation. . Each spillway is equipped with four 100-foot drum gates that act across a sixteen-foot vertical dimension.
Water flowing through the lowered gates into the spillway reservoir falls 600 feet downward through the tunnels to re-enter the river downstream of the dam. The Boulder Dam Power Plant is built in two wings, a single one on each side of the canyon wall at the downstream foot of the dam. The first generator was put into operation on September 11, 1936. Equipped with seventeen generating units, with capacities ranging between 40,000 and 82,500 kilovolt amperes, this, the largest power plant in the world, is capable of generating 1,835,000 horsepower. force of electrical energy when operating at maximum power. rated capacity. The transmission lines carrying power from Boulder Dam radiate in a network from the dam with the main lines serving the Los Angeles metropolitan area.
From the intake structure located on the roof of the power plant, the lines pass along the edge of the canyon to the switching yard, where the most modern and specialized developments in the field of power transmission are located. From the switchyard, the lines travel across the desert bringing light to homes and cities and power to the factories of the great southwest. From Parker Dam, 150 miles to the south, the Colorado River Aqueduct supplies the city of Los Angeles with domestic and industrial water supplies. While from the Imperial Dam, 300 miles to the south, the All-American Canal diverts water from the Colorado River to the rich agricultural districts of the Imperial Valley.
And this is what the Boulder Dam looks like today, a modern colossus, resting on the rock walls of the Black Canyon, resisting and controlling floods and bending the will of a hitherto ungovernable current, the Colorado River, to carry out the fruitful tasks of a rapidly encroaching civilization. the limits of its last frontier.

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