Sean's Earth Science Blog: Underground Mining Methods

Drift Mining

This type of mining is one of the earliest coal mining techniques. Drift mining is done when the coal seam is at the same elevation as the outside is so miners can simply enter the mine without having to go down shafts. It can be used when the coal seam intersects the surface while the mine layout follows a horizontal direction with the coal.

Advantages:

- Cheapest way to mine.

- Doesn’t demand much machinery.

- Less effort is needed to reach the coal.

Disadvantages:

- Coal located below the drift cannot be accessed using this method only.

- Tunnels could collapse and trap miners inside.

Simple Drift Mine Diagram

Shaft Mining

When coal is not accessible through drift mining, shaft mining is used. Shaft mining is used when coal is located well below the surface and must be accessed by going deep underground, sometimes 1000 feet or more. Working elevators are placed into shafts and extend down to the same level as the coal seam. One shaft is used for the transportation of miners and their equipment and the other is used for the transferring of coal to the surface where it can be processed.

Shaft Mining Diagram

Advantages:

- Coal found deeper in the Earth can be accessed.

- Two elevator system moves coal and miners separately, saving time.

Disadvantages:

- Can become expensive if coal is located deep in the earth.

- Potentially dangerous because exit requires an elevator.

Room and Pillar Mining

Room and pillar mining is used after shafts have been dug underground to transport miners to coal waiting to be mined. Once the miners and their equipment reach the coal, pillars of soft, bituminous coal hold up the roof of where the miners are working and the coal around them is extracted. This is not a safe and effective way to mine; roof falls are common due to the pillars “squeezing” and putting pressure on other pillars and the roof can collapse. Half of the coal in the mine must be left alone because it holds up the roof, making this mining method ineffective and unsafe.

Room and Pillar Mine

Advantages:

- Manmade pillars don’t need to be transported down to the mines.

- Mining areas can have a flat surface, making it easier to use machinery.

Disadvantages:

- Dangerous due to soft, coal pillars holding up immense amounts of pressure above the mine.

- Very inefficient; half of the coal must remain unused to provide support for the roof.

Continuous Mining

Continuous mining is a mining method commonly used alongside drift and room and pillar mining with technological innovation added in. Heavy machinery is used to greatly increase mining efficiency. These machines are equipped with tungsten carbide teeth to capture many tons of coal in a small amount of time. Along with the mining machines, conveyor belts transfer the coal to its appropriate location after extraction. The technological advances make continuous mining much more economical than the traditional pick and shovel and donkey-pulled cart system.

Continous Mining Machine

Advantages:

- More coal can be mined quicker with the use of the machines.

- The job only requires one miner to operate the machinery, saving the company money and if an accident were to occur, only one miner could be harmed instead of many.

Disadvantages:

- Room and pillar mining is still used in conjunction with continuous mining, which still leaves potential danger for roof collapses.

- Machinery may be difficult to transport and upkeep in the mine, sometimes deep in the earth.

Longwall Mining

Longwall mining is the most productive mining technique. This procedure uses a gargantuan machine that supports the roof above while steadily collecting all of the coal in its path. When finished, the machine retreats and the coal roof above falls. After the roof falls, the machine proceeds to pick up the remaining coal from the roof and is transported out. This is the most efficient way to mine due to all of the coal being mined, including the coal above, and none being left behind for support like in room and pillar mining.