Question 13
- Define the term mine.
- Write explanatory notes on:
- the room and pillar method of coal mining;
- the longwall method of coal mining.
This question was fairly popular among the candidates and their performance was poor. A good number of the candidates gave definition of Mining for that of a mine. A mine is an opening made in the earth for extracting useful minerals.
The following should be noted about the room and pillar method of coal mining:
- It involves the extraction of coal by creating rooms
- Pillars of coal are left unremoved at regular intervals in between the rooms to give support
- After the removal of coal, crosscuts are made at right angles to the general direction of mining
- The size of the pillars that is used in supporting the roof should be the same dimension
- The rooms and cross cut could be created using two system namely- the conventional mining system and continuous mining system.
- The conventional mining method involves creation of kerf/slots at the floor on the surface of the coal
- Holes are drilled into which permissible explosives are used to blast off the coal
- Loading machines are used to evacuate the blasted pieces of coal
- The main entry point is created on evacuation of the blasted coal
- The continuous method involves the use of a highly integrated machine
- The machine rips off coal from the mine face
- Broken coals are rolled automatically to an inbuilt conveyor belt which rolls them to the collection point at the rear (back) of the machine.
- Proper arrangement are made for mine ventilation
- Provisions are made for seepage water
- Care is taken to give the required support for the roof of the mine
The following should be noted about the longwall method of coal mining:
- Unlike the room-and-pillar method, this method leaves little coal unmined in the pillar.
- Large panels of coal are created
- The faces are mined in slices back towards the shaft
- Coal is usually skimmed from the face using a shearer machine
- The face conveyor moves the skimmed fragments of coal to the permanent conveyor in the main entry.
- Massive hydraulic jacks are used to support the roof of the mine
- The face conveyor and powered support are repositioned as the mining progresses
- The roof of the mine is allowed to collapse in a regulated manner at the gob/goaf