Quarrying 242


Quarrying is the process of taking stones from their natural rock bed. Many factors may determine quarry site. They include

  • Haulage facilities of quarry material
  • Availability of good building stones
  • Sufficient damping site for quarry refuse
  • In case of quarry blasting, there should be sufficient distance between quarry from buildings.

QUARRYING METHODS

  1. Quarrying by hand tools
  2. Quarrying by channeling machines
  3. Quarrying by blasting

Quarrying by Hand tools

It includes :-

  • Excavation – Stones are extracted by hammers, peak axis, shovels, chisels e.t.c
  • Heating – To remove portions of blocks by heating i.e fuel used.
  • Wedging – method of quarrying soft stratified rocks. i.e in this method 10-16 cm deep holes about 10 cm apart are drilled along boundary of stone to be quarried. Steel plugs are inserted by sledge hammer which blows  on the wedges. for softer rocks wooden pegs are used instead of steel plugs.

Quarrying by Channeling machines

In this method machine driven by steam compressed air or electricity is used to make channels cutting rock mass, horizontal holes are drilled beneath the block, wedges are driven into the holes and finally rock is broken loose from its bed.

Quarrying by blasting

This is the quarrying of stones by use of explosives. it is mostly done to metamorphic rocks because they are compact and do not have fissures.The purpose of blasting is to loosen large masses of rocks not exactly to blow up the whole area. it is done by first drilling the desired hole, filling holes with explosives and finally firing the charged explosives.

TOOLS USED IN BLASTING

  1. Jumper – It is used to blast a hole by striking.
  2. Scrapping spoon – This is used to remove crushed stones from drill holes
  3. Priming needle – used to maintain a hole while tamping is done and provides passes for insertion of a fuse to cause explosion.
  4. Tamping rod – used for tamping explosives and earth into the hole.
  5. Dipper – used to drill hole to required depth.

PRECAUTIONS AGAINST BLASTING

  1. Blasting activities should not be carried out in late evening or early morning. it should be carried out in times well known to people around blast area.
  2. Red danger flags should be prominently displayed at a safe distance of around 200m or around area of explosion.
  3. Before actual firing a siren should give prior warning to the workmen and other people to clear the blast area.
  4. the blast men must certify that all charges have exploded by comparing no of charges with fixed no of explosions heard.

N.B

MISFIRES

  1. Misfires can prove to be very dangerous, in case of doubt sufficient time should be given before entering blast area.
  2. Withdrawal of a charge that has not exploded is a complete NO…….. NO. The hole should be flooded with water and marked in bold.
  3. Boreholes must be thoroughly cleaned before inserting a charge in them.
  4. If the misfire is because of defective explosive,detonator or fuse the whole of material should be taken for checkup.
  5. In case of misfire a another hole should be bored at a distance of 500m and blasted as usual.

PROCESS OF BLASTING

  1. Blast holes are made and cleaned by using tools
  2. The charge of explosive is placed at the bottom
  3. Clay is the inserted and tamped into the blast hole
  4. A fuse is inserted and kept projecting above rock surface
  5. Projecting end of fuse is fired by detonator.

 TYPES OF EXPLOSIVES

  1. Blasting powder – it contains 65% potassium nitrate, 20% sulphur and 15% charcoal
  2. Dynamite – it contains 75% nitroglycerine absorbed in 25% sandy earth hence forming a thick paste.
  3. Gun cotton/ Nitrocellulose – it is made by circulating cotton in nitric acid.
  4. Blasting gelatin- This is 93% nitroglycerine and 7% gun cotton.
  5. Cordite – it is a powerful smokeless explosive in which nitroglycerine is used.
  6. Gelignite – It is a powerful and convenient explosive  i.e 65% blasting gelatin and 35% absorbing powder. it can be used under water.

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