Stone Quarrying

What is stone quarrying ?

Stones are not directly available in nature for engineering use. It is always taken out from a natural beds of rock. This process of taking out stones from a natural rock bed is called as quarrying. Many students get confused between quarry and mine but, both are different the word quarry used to indicate exposed natural surface of rocks. So that in case of quarry operations are carried out at the ground surface. While in case of mine operations are carried out at greater depth below the ground surface. 

To select a quarry is not just that simple, we need to take care of few things before the selection of site get done.

Site selection for quarry 

Before selection of quarry following aspects should be studied carefully.

1. for any type of work 4M availability studied first i.e. manpower, machinery, material and money.
2. distance of site location from transport facilities like road, railway, airport and sea coast etc will affects economy.
3. drainage facilities.
4. stone carrying and conveying facilities for quarry.
5. local geological data and expertise for information and guidance related to rock formation.
6. quality and quantity of stones available from quarry site.
7. results of trial pits. 

Stone quarry is not selected on random basis it needs to be specific for its consideration.

Stone quarry selection

To consider any rock surface as a stone quarry we need to pay attention to the followings:

• Rock surface
• Layout of quarry
• Men and machinery
• Top surface removal
• Structural stability etc

1. Rock surface

Before any execution of stone quarrying rock surface should be carefully studied. Location of cracks and weak spots noted. Plane at which rock can be easily split into two parts found out and use for future quarrying which is easy and economic. Operations should be quick.

2. Layout

Before quarrying operation complete layout of various stages involved in quarrying should be prepared. If layout not prepared carefully and faulty planes are ignored it will leads to failure of quarrying operation and chances of damage to the equipment's increases.    

General Flow Chart

3. Men and machinery

For any type of work a perfect coordination between men and machinery needs to be established. Operator should be aware of complete knowledge of machinery's specification. So that maximum advantage and output can be ascertained.  

4. Top surface removal

Due to weathering effects top surface of quarry rocks are loose and soft in nature, which can not use for construction work hence it is rejected. So as to minimize the chance of rejection of material, top loose and soft material is to be removed before quarrying. Dense and hard rocks available at certain depth below the top surface obtained for construction use.

Top Loose Surface

5. Structural stability

Stones taking out from rocks needs to take care for its structural stability, as there may be chance of weak spots which will cause landslide or failure of whole. So as to ensure no accident condition, precautions are taken that while removing stones from quarry it will not affects stability.

Short Clip

How quarrying is done ? 

Quarrying operation is not same for all location, it will differ location and conditionally, following are some methods which are used for different purposes.

1. Digging

Digging is done with the help of suitable machinery. Digging is done in case of soft stone in the form of large or small blocks.

2. Heating

Some of the rocks needs to be heated before quarrying operation at the surface. Surface can be heated by placing wooden plates on rock and setting fire on it. Due to heating unequal expansion of surface upper layer of rocks separate out. It is indicated by dull bursting noise. Detached portion of the surface is then removed by suitable instruments. This method is useful for rocks having horizontal layers at shallow depth. This method is used for small regular shape blocks from quarry.

3. Wedging

This method is used when rock surface contains cracks or fissures steel wedge or steel point is used accordingly and they are driven through hammer. Blocks are then shifted from location and steel wedge or steel point removed from it. 

Sometimes natural cracks or fissures are not available, at that time we need to form an artificial crack. Artificial cracks are formed by following way.

• A series of hole drilled on rock surface.
• Diameter of holes maintained about 12 mm.
• Center to center distance between holes is kept about 10 cm to 15 cm.
• Depth of hole kept about 20 cm to 25 cm.
• Plug and feather are placed in hole as shown in figure.

• 

  Plug and Feather

  
  

After following above procedure a great pressure is exerted  and a crack is formed along the line of holes. If stone is comparatively hard, pneumatic drill may be employed to prepare holes for plug and feathers.

If rock is soft than wooden plugs may be used. In this method wooden plugs are soaked with water and let it swell freely which exert great extent pressure on soft rock and split it into parts.

Wedging is operation is employed for following rocks:

• Laterite
• Marble
• Limestone
• Sandstone.

Wedging will always be better and preferred than blasting, wherever it's possible.

4. Blasting

Sometimes hard rocks are present in location and no cracks or fissures available, can not be extracted from any of above three methods. At that time we need to use blasting method for converting rocks into pieces. 

Stone pieces available form this method is hard and strong enough, so that they are used as railway ballast, aggregate for structural use, road metals etc.

Further blasting operation in detail we will study in next blog.

"To Be Continued..."