Used at building and mine sites, dump trucks dig up and move tons of dirt, rocks and sand. Some of these machines are so big that they can’t be driven on streets or highways, and instead are shipped in pieces from the factory to the work area, where they are then put together.
The Caterpillar 797B is the largest mechanical dump truck inthe world at 14.m in length. It weighs 306 tons, with each tyre being 4m high -taller than a basket-ball hoop. The truck is taller than a two-storey building, and its height doubles when the back of the dump truck, called a bed, is tilted to dump its load. This type of dump truck can carry up to 380 tons of thick, oily sand dug from a mine.
A giant dump truck needs a loader almost as big to fill it up. With its bucket raised, the largest loaders reach over 13 metres in height.
A worker in the loader operates the machine’s bucket, which scoops up sand or other materials and lifts it over a dump truck. The bucket then tips and drops the material into the dump truck’s bed. Loaders can hold up to 80 tons -similar to lifting more than 1,000 adults at once.
Similar to a loader, a hydraulic shovel is used at mines to lift heavy loads of coal, rock and sand. Liquid flows inside the machine, which creates pressure that helps the shovel move and lift.
The world’s largest hydraulic shovel is the Terex RH 400 -pronounced T-rex, it’s named after the dinosaurs because it is so large. It’s over 13 metres long and can lift 94 tons.
Some earthmovers just move earth, but most bulldozers can tear up the ground and push it away.
At the rear of some bulldozers is a steel spike, called a ripper, whichcan be pushed into the ground like a sharp claw. The bulldozer then moves away and the ripper does its job, easily tearing up solid rock or concrete.
Bulldozers also have a wide blade at the front, which can push about 240 tons of earth -enough power to push a large airplane. Bulldozers tear down houses, buildings or trees that stand in their way, and of course, move earth.
Instead of tyres, bulldozers move on rubber or metal tracks that help them grip the gound. The wide tracks also spread out the machines’ huge weight so that they don’t sink into the earth.
Most substances that modern man uses is mined from the earth. Mining provides such things as iron, aluminium, gravel, salt, diamonds, and silicon for making computer chips. Coal is mined to provide energy -in days past it was commonly used in peoples homes to provide heating, but now it is mostly used to transform the above-mentioned raw materials into finished products. Most substances obtained through mining are classified as minerals, but that term generally excludes coal, petroleum, and natural gas.
Some valuable substances are found at the ground’s surface and can be mined cheaply, but others lie far beneath the surface and can be removed only by deep underground mining.
Around 3500 BC, people began mining tin and copper. They combined these metals to make bronze, a harder alloy for use in making tools and weapons. The ancient Romans recognised that mining metals could make a nation rich and powerful, and took over the mines of the countries they conquered, mining gold, silver and lead. The Roman Empire split apart in the AD 400s, and very little mining advancements occurred over the next thousand years.
In the 1400s, coal, iron and other materials were mined in Europe and in South America, and in the late 1500s European miners began using gunpowder to blast through rock, with this practice becoming widespread by the 1700s.
Mines are built where a mineral is not too difficult to recover, some lying near the surface, and others far underground. To be considered worth mining, a deposit must contain a sufficient quantity of ore, rock or earth from which the mineral can be extracted at a profit.
Mining techniques vary based on the location and shape of a mineral deposit and experts generally divide mining methods into three categories: Surface, underground, and hybrid.
UNDERGROUND MINING METHODS
There are several underground methods. Drift mines have horizontal (level) openings, and generally occur where ore reaches all the way to the surface. Slope mines have a downward incline that leads to deeper deposits of ore. Shaft mines use completely vertical shafts to reach ore deeper than about 230 metres beneath the surface of the earth.
There are three categories of mining techniques:
Self-supported mining techniques rely on the ore itself to suport workers and the overlying material. Workers excavate as much coal as possible from a horizontal deposit, leaving pillars of coal to support the rock above. This technique is used for flat deposits of coal. A similar technique called stope-and-pillar mining is used for thicker and more irregular horizontal deposits of minerals such as limestone, salt and potash.
Another self-supported mining technique called shrinkage stoping, progresses upward and uses blasted and broken ore as a work platform for further mining.
Broken rock takes up more space than solid rock. Some of the rock must therefore be removed from the stop (excavate area) to provide space afor further drilling and blasting.
Vertical crater retreat mining, a patented self-supported mining method, uses specialised explosives to break the ore from the bottom upward. Workers can leave the broken ore in the stope to help mainatin the stability of the stope walls.
Supported mining typicall uses the cut-and-fill technique, where miners remove horizontal ‘slices’ of ore, starting at the bottom of the ore and move upward. After excavating a slice of ore, miners fill the hole with waste material from ore-processing plants, often adding cement to increase the strength of the fill. This material supports the walls and provides a working platform fro which to mine the next ore slice.
Caving techniques allow parts of the mine to collapse or cave, under controlled conditions.
Longwall mining is an extremely efficient caving technique. Using a machine to cut or break ore from a single face that can be up to 360 metres long, hydraulic roof supports hold up the roof above the miners, and as they dig farther into the seam, the supports advance with them, and the roof behind the hydraulic supports collapses.
In block caving, miners divide the ore into large panels or blocks. They then undercut a panel with a horizontal slot. The rock and ore above the slot fracture and cave into the slot. Large machines remove the ore from the slot and transport it to vertical or inclided ipenings, whre it is removed from the mine.
Pumping methods involve the the extraction of minerals in a liquid form. The waters of the ocean and of some lakes, contain huge amounts of dissolved minerals, and miners obtain these mineral by pumping the water into plants where it is treated. In such plants, pumps move large amounts of water through devices called precipitators that draw the mineral out of the wter. Much of the magnesium used today is obtained by this method.
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