Case Study on the Hoover Dam
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Hoover Dam
After
By- Balaji.T.K, CE02B011
CONTENTS
Description
Page no
Hoover dam -an Introduction
Requirements posed by structural design
Requirements posed by other details
Type of Concrete
Guidelines for Mix design
Fabrication and Installation
Formwork
Cooling of concrete
Temperature control of Mass Concrete
Quality Assurance
Bibliography
Hoover Dam- an Introduction!
It still stands tall as an engineering marvel high above the Colorado River between Arizona and Nevada. Hoover Dam attracts over 7 million visitors from around the new world every year feeding vast tourism into the Las Vegas Nevada and Arizona economy.
The building of Hoover Dam took the brilliance of over 200 engineers to pull-off what many deemed as almost impossible. And it was the fortitude of over 7,000 dam workers that endured amazingly harsh conditions and extreme dangers to complete Hoover Dam almost two years ahead of schedule
The Mission of the Dam:
Flooding along the Colorado River as it made its way to the Gulf of California had to be controlled.
The water-flow had to be harnessed to provide much needed water to the fertile, yet arid agricultural areas of California and Arizona.
Hydroelectric energy was to satisfy the requirements of millions and millions of people in adjacent regions.
Some Statistics About the dimensions of the dam:
Hoover Dam is 726 feet tall and 1,244 feet long. At its base, Hoover Dam is 660 feet thick which is 60 feet longer than two football fields laid end-to-end. Combined with its top thickness of 45 feet, there is enough concrete (4.5 million cubic yards) in Hoover Dam to build a two-lane highway from Seattle Washington to Miami Florida. Or imagine a four-foot wide sidewalk around Earth at its equator.
A scenic by-product of Hoover Dam is the gigantic reservoir of Lake Mead, a stunningly beautiful water recreation wonderland. This boating, sailing, fishing and house-boating paradise attracts over 10 million visitors a year. Lake Mead covers 550 miles of majestic shoreline and 247 square miles of area which is twice the size of Rhode Island. Its capacity of 1 1/4 trillion cubic feet of water would cover the entire state of Pennsylvania one foot deep.
Requirements for concrete posed by Structural design:
The Hoover Dam is an arch dam. Arch dams transmit most of the horizontal thrust of the water stored behind them to the abutments by arch action and hence thinner cross sections are sufficient (compared to the massive cross-sections of the gravity dams). Narrow V-shaped canyons(just like the Black canyon where the Hoover dam was constructed) will be suited for locating arch dams since they can withstand the thrust produced by the arch section.
Fig 1 Free body Diagram of an arch dam
Fig. 2 Constant Radius Arch Dam
Fig 3 .Constant Angle Arch Dam
Fig 4 Variable-Radius Arch Dam
Fig 5 Double curvature – Cupola Dam
Vertical curvature is introduced the weight of the dam will offset vertical tensions due to
water load. Cupola dams are ideal for narrow valleys and are similar to the thin arch dams in regard to foundation requirements.
In other words, the design considers action of segments of vertical cantilevers and horizontal arches working simultaneously. The object should gain the same deflection at their point of intersection with a water load on the face and with varying thicknesses of the dam.
As Hoover Dam is one of the largest in the world, it bears a tremendous amount of load due to the hydrostatic pressure of the water stored in its reservoir.
Therefore, some of the possible structural requirements are listed below.
The concrete to be used should be able to bear large loads.
Tunnels to divert the flow of the river to construct the dam.
Before actual Hoover Dam construction could begin, the Colorado River had to be temporarily diverted around the dam construction site. To divert the rivers flow around the construction site, four tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were to be 56 feet in diameter. Their combined length was nearly 16,000 feet (more than three miles).
Tunneling began at the lower portals of the Nevada tunnels in May 1931. Shortly after, work began on two similar tunnels in the Arizona canyon wall.
To construct such tunnels the requirements for the concrete would be:
It should withstand the pressure due to the rushing water in the tunnel. But, the it does not require the same strength as the concrete used for building the dam itself.
The concrete should be highly fluid so that it could be easily poured into whatever shape that is chosen for form works.
3. The concrete should be abrasion resistant.