DEFINITION- The process of taking out stones from natural rock beds is known as the quarrying. The term quarry is used to indicate the exposed surface of natural rocks. The stones, thus obtained, are used for various engineering purposes. The difference a mine and quarry should be noted. In case of a mine, the operations are carried out under the ground at great depth. In case of quarry, the operations are carried out at ground level in an exposed condition.
SITE FOR QUARRY
The selection of site for a quarry of stones should be done after studying carefully the following aspects:
1. Availability of tools, power, materials and labour for the efficient working of quarry.
2. Easy availability of clean water in sufficient quantity all the year round.
3. Economy in quarrying.
4. Drainage of quarrying pit.
5. Facility of carrying and conveying stones from quarry.
6. Quality of stone available from quarry.
METHODS OF QUARRYING
Following are the three methods of quarrying:
I. Quarrying with hand tools
II. Quarrying with channeling machine
III. Quarrying with blasting.
QUARRYING WITH HAND TOOLS
There three methods of doing this type of quarrying:
a) Digging or Excavating
(a) Digging or Excavating- In this method, the stones are merely excavating with the help of suitable instruments such as pick-axes, hammers, showels, chisels, etc. This method is useful when a soft stone occurs in form of large and small blocks.
(b) Heating- In this method, the top surface of rock is heated. This method is useful when small blocks of more or less regular shape are to be taken out from quarry. It is suitable when the rock formation consists of horizontal layers of shallow depth. It is possible to obtain by these method fairly rectangular blocks required for coursed rubble masonary.
(c) Wedging- In this method, if rock surface contains cracks or fissures,the steel wedges or points, as shown in fig., are driven through such cracks by means of hammers. The blocks of stones are then shifted and they are removed with the help of suitable instruments.
The wedging is adopted for costly stratified rocks which are comparatively soft such as laterite, marble, limestone, sandstone, etc. The wedging is preferred to the blasting, wherever possible.
QUARRYING WITH CHANNELLING MACHINE:
In this method, the channeling machine driven by steam, compressed air or electricity are used to make vertical or oblique grooves or channels on the rock mass. These machines make rapidly the grooves having length of about 24m, width of about 50mm to 75mm and depth of about 2.40m to 3.70m. The process consists of the following steps:
(a) The channels are cut around the stone block which is to be removed from the rock mass.
(b) The horizontal holes are drilled beneath the rock.
(c) The wedges are driven into the holes and the block is then broken loose from its bed.
QUARRYING WITH BLASTING:
In this method, the explosives are used to convert into small pieces of stones. The main purpose of quarrying stones by is to loosen large masses of rocks and not to violently blow up the whole mass so as to convert it into very small pieces of practically no use.
This method is adopted for quarrying hard stones, having no fissures or cracks. The stones obtained by blasting are usually of small size and they are used as ballast in railways, aggregate for concrete, road metal, etc. The process of blasting is important with respect to the stone quarrying.
Commonly used Stones in India.
• Origin and composition: – it is a most common variety of metamorphic rock. It is formed from crystallized limestone by metamorphism, chemically, it is calcareous and is chiefly composed of calcium carbonate.
• properties:- following are the properties of marble:
• its crushing strength is from 500 to 600 kg/cm2
• the usual color of marble is white, but it is also available in different shades of colors such as grey, black, red, brown, yellow and combination of these
• it is compact and crystalline in structure due to which it can take a fine polish
• it is les durable
• Itcan be carved easily and thus is most suited for sculpture work.
• its specific gravity is 2.72 its weight 2720 kg/cum
• its absorption is 1 to 3%
• Chief uses:- used as building stone and in decorative panels
• Origin and composition:- This stone is a common variety of sedimentary rocks mechanical origin. it is physically, stratified and chemically, siliceous in siliceous in nature, it is chiefly composed of quartz (grains of sand) bound together by a cementing material, but other minerals such as felspar, mica, magnetite etc. are also present.
• Properties:- following are the properties of sand stone:-
• it’s crushing strength is 400 to 650 kg/cm2
• It is white, grey, yellow, light brown, and red in color.
• Its specific gravity is 2.3 to 2.4. Its weight is nearly 2350 kg/cu m.
• Chief uses:- general walls building flagstone.
• its crushing strength varies from 700 to 2100 kg/cm2
• it is hard tough and is least absorptive
• It also offers good abrasive resistance.
• It is a good heat and electrical insulator.
• Its water absorption varies from 0.5 to 1%.
• Following are the uses of slate.
• It is a valuable material for roofing and black boards.
• Thick slabs of harder variety of slates are used for flooring steps shelves mental pieces sills of doors and window etc.
• slate a available at the available at the following localities in India:-simla, kangra, gurgaon, Gurdaspur, Alwar, Rajasthan, (MP) (Haryana) (Gujarat
• Origin and Composition: these stones are the common varieties of igneous rocks they are formed by solidification of lava on the earth’s surface due to volcanic eruption. Some basalts develop step like appearance and are known as traps. They are chiefly composed of silica, alumina and felspar.
• Properties: Following are the properties of basalt and trap
• Their crushing strength is 700 to 850 kg/sq.cm.
• They are hard and tough
• They are greenish grey to dark grey in color.
• Their specific gravity (2-9 to 2.96) is more than that of granite their weight is nearly 2900kg/cm3.
• They are available as a vast deposit of basaltic rock, near the western Ghats of India, known as Deccan trap. They are also available at Rajmahal Hills (Bihar) known as Rajmahal Trap. Varieties of basalts jike, Bombay Basalt, Blue basalt, red basalt and yellow basalt are found and used in Maharasatra, Gujarat etc.
• Color:- White light grey to light buff.
• Texture:- fine to crystalline, may have fossils
• Parting:- parallel to beds: also may have irregular fractures.
• Hardness:- fairly soft steel easily catches
• May show fossils.
• All lime stone are of sedimentary origin and have for their principal ingredient carbonate of lime.
• When clay is present, the stone is called argillaceous limestone; when silica predominates, siliceous limestone; when iron is prevalent, ferruginous limestone; when magnesia is present to the extent of 15 per cent.
• Granite is one of the most valuable stones for construction purposes. Although the quality of granite varies according to the proportions of the constituents and to their method of aggregation, this kind of stone is generally durable,strong, and hard.
• The hardest and most durable granites contain a greater proportion of quartz anda smaller proportion of feldspar and mica. Feldspar makes granite more susceptible to decomposition by the solution potash contained in it, potash feldspar being less durable than lime or soda feldspar.
• Because of its uniform structure, granite can be quarried in large blocks. The rift, the grain, and the joint planes are advantageous in quarrying, as it is very difficult to cut granite in other places. The uses for which granite is suitable depend on the texture of the stone. Medium-grained stone is best fitted for building construction. Fine-grained stone can be carved and polished.
• Schist has a more crystalline structure than slate, and the crystals are easily seen. It is composed chiefly of minerals that cleave readily, such as hornblende, mica, etc., mixed with a variable amount of granular quartz and feldspar. The presence of the cleavage minerals produces a fine cleavage or foliation, called schistosity.
• Schist is sometimes used in building construction but it disintegrates very rapidly and is not durable. It should always be set with the planes of schistosity horizontal.
• Gneiss is a coarse-grainedlaminated rock.
• It is formed by metamorphism of either sedimentary or igneous rock.
• It is oftenused as structural material and as concrete aggregate.
• Shale is a typical clay rock that splits readily in lines parallel to the bedding.
• Sand and lime carbonate are always present in this stone and, with increase of either, the rock grades into shaly sandstone or shaly limestone.
• Shale is used for light traffic roads and in the manufacture of brick,tile, and other burned clay products, but it is not suitable for concrete aggregate.
• Stratified rock composed of rounded pebbles of any material, such as limestone, quartz, shale, granite grains, feldspar, etc., cemented together is known as conglomerate.
• When the pebbles are quartz with siliceous binding the rock is strong and hard to quarry or dress.
• When the interstices between the pebbles are not filled by the binder, the rock is very porous, and may hold great amounts of ground water.
• This stone is seldom used in building construction.