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A walking dragline is a heavy duty industrial machine typically used for surface mining and civil engineering applications. It is similar in design to a crawler crane but instead of a hook, there is a large bucket that is suspended from the lengthy boom. The bucket is controlled by wires and chains to excavate large quantities of earth and deposit it at a location away from the dig site. A walking dragline literally walks, as individual beams rise and fall to move the machine forward. The average walking dragline typically weighs a few thousand tons, but manufacturers have constructed draglines that weigh as much as 13,500 tons (about 12,250 MT).
The dragline was invented in 1904 by John W. Page for use in the construction of the Chicago Canal. His invention would be modified and expanded on by Oscar Martinson in 1913 to create the first walking dragline. Later on, advances in hydraulic mechanisms allowed operators to expand the use of the walking dragline, especially in rugged terrain. With increased mobility and ever-increasing bucket capacity, the walking dragline became an invaluable tool to miners and engineers.
One limitation of the walking dragline design is that the radius within which the excavated material can be dumped is dependent on the length and height of the boom. This generally leads to storage problems, thus requiring modifications around the dig site to safely accommodate the large concentration of excavated dirt. Another limitation is the excavation depth, which is limited by the length of the dragline rope. Also, walking draglines are not efficient at removing mounds of earth that rise above its base, thereby requiring more electricity and time than a standard excavation would typically require.
The largest walking dragline ever created was aptly named Big Muskie. It was the largest mobile excavation machine on Earth, weighing in at 13,500 tons (about 12,250 MT) and standing nearly 223 feet (almost 68 m) high. The hydraulically driven machine required 13,800 volts of electricity to excavate 325 tons (about 295 MT) of dirt with a bucket that had a capacity of 220 cubic yards (about 168 m3). From 1969 to 1991, Big Muskie moved nearly twice the amount of earth that was excavated during the construction of the Panama Canal and more than 20 million tons (about 18.1 million MT) of clean coal. In 1999, the cable holding the massive boom was cut by explosives, effectively scrapping Big Muskie.
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