Quarrying of Stones without Blasting and with Blasting

Process of quarrying is the process of collecting stones from the natural rock surfaces. Quarrying of stone is completely different from mining. Mine belongs to underground operation only. Whereas, quarry is carried out on exposed surface of natural rocks. So, the stones collected through quarrying is used for various engineering purposes. Stone quarrying is generally done at hilly areas where large quantity of stone is available. In fact, stone quarrying is the multistage process by which rock is extracted from the ground. Extracted rock is crushed to produce aggregate, which is then screened into the sizes required for immediate use, or for further processing.

Quarrying Methods

Quarrying methods are classified differently. It is convenient to divide them under two main headings. namely, quarrying without blasting and quarrying by blasting.

1.1 Quarrying of Stones without Blasting

In these methods, blocks of rocks are broken loose from their natural outcrops by men. In this method, men use hand tools or special purpose channeling machines. No explosive material is used at any stage in this method of quarrying of stones. Soft rocks and also those rocks which have layered structure are easily quarried by these methods. As a first step, the loose cover of soil over the rock. It is first removed and the rock surface is cleared It is then systematically broken into blocks of desired sizes. This is done either by driving wedges or by cutting channels.

The Wedge Method of Quarrying

It is consists of digging a few holes at carefully selected places on the rock. These holes are dug either manually using chisels or hammers by the skilled workers. Or, in major quarrying, these holes may be drilled by special machines called hammer drills. Once the hole is ready, a steel wedge is inserted in between two steel strips or feathers. This is done with all the holes drilled in a sequence. Such firmly inserted wedges are then struck with a hammer almost simultaneously. This process develops cracks along the lines joining the holes. After that, long iron bars are inserted in the holes and cracks, and then the blocks of the rocks are pushed forward onto the free face of a quarry.

The Channeling Method of Quarrying

This method of quarrying, involves the use of big machines . These big machines are called Channelizers which have reciprocating cutting tools and are power driven. When single large blocks of costly stones like marbles and limestones are required, this method is most suitable. The channelizer can cut a groove as deep as 3 meters and as long as 3 meters, or even more. When a single block is required, grooves of required depth and length are first cut at the back and sides of the working face of the quarry.

Holes are then drilled from the free front side horizontally to meet the back channel at its base. Using wedges and rods, the block is separated from the rock and hoisted up to the transporting Lorries or wagons. Single blocks as big as 10 meters long and 3 meters thick and 1-3 meters wide can be quarried by this method from soft rocks.

 

Quarrying by Heating

It is an old, crude method which may be useful locally for obtaining small quantities of stones. Rocks are heated for a few hours by burning heaps of firewood over their surface. Such a process results in expansion of the upper layers and their cracking and separating from the lower layers.

1.2 Quarrying of Stones by Blasting

This method consists of using explosives for breaking stones from very hard rocks. It has been observed that quarrying of granites, basalts, traps, quartzites, and sand-stones by wedging and other methods is very laborious and costly. These hard rocks, however, can be loosened economically and easily by using explosives. The basic principle of this method is to explode a small quantity of an explosive material at a calculated depth within the rocks.

The force generated due to this explosion is sufficient only to create cracks and loosen blocks of good size. Blasting for quarrying for stones may be quite different from blasting for road clearance. In the latter case, the size of the broken stone is of not much consequence. Quarrying by blasting, therefore, requires very experienced persons. These people must be thoroughly acquainted with blasting explosives on the one hand and strength qualities of rocks on the other hand. Quarrying by blasting involves a series of systematic operations. Drilling of blast-holes, charging of blast-holes and firing the shots are some of these operations.

Drilling of Blast-holes

A blast-hole is a hole of suitable diameter and depth driven at a properly selected location on a rock for being charged with an explosive. It may be driven either manually or mechanically. In mechanical drilling, machines such as hammer drills, percussive drills or rotary drills are used depending on the nature of the rock.

In the quarrying by blasting, the diameter, depth, number, and spacing of boreholes require very careful considerations for getting the most beneficial result. The diameter of the hole is determined with the type of explosive being used. For explosives that come in standard sized cartridges, the diameter has to be slightly greater than the size of the cartridges for allowing easy insertion.

Points about Blasting Powder

Bu when blasting powder has to be used, the diameter of blast-holes will depend on the quantity of explosive to be accommodated as also the convenience of drilling the holes. The depth of blast-hole depends on the volume of rock to be broken in one shot which is also related to the quantity of the explosive that has to be charged into the hole. The Spacing of holes has to be decided carefully when a number of holes are to be charged and fired simultaneously. A given quantity of any explosive can induce cracks, break open or throw away limited volumes of rock around it on exploding.

Naturally, when holes are too closely spaced, they will shatter the rock into smaller, useless pieces. When they are spaced too far off from each other, cracking caused on their explosion will not break the entire aimed rock mass in the desired manner. Properly spaced holes charged with calculated quantities of explosive will not only break the calculated volume of rock into blocks of manageable size but also throw them at a proper distance from the quarry. While spacing the holes, the distance from the free side of the quarry is kept into consideration.

On exploding, the main thrust is along the shortest distance to the free side. This distance is called the line of least resistance. If this line is of considerable length, the shot may prove effective. Similarly, if this distance is too short, the broken stone may be thrown far away from the quarry.

Charging of Blast-hole

The loading or charging of the blast-holes with pre-determined quantities of the selected type of explosive is to be done with great care and caution. A slight negligence in this operation may lead to fatal accidents.

Following are some important steps to keep in mind while charging the blast hole:

The holes are first cleared of all the obstructions and irregularities with the help of wooden romping rods.

Explosive in the form of powder packs or cartridges is then inserted in small quantity at a time.

Before adding the next batch of explosive, the previously placed quantity is packed firmly by using wooden tamping rods. Metallic rods are never used.

Fuse Insertion

When blasting powder is used as an explosive charge, a fuse is inserted. In the case of charge is in the form of cartridges a primer cartridge which has a highly sensitive explosive, it is also inserted and is connected to a safety fuse. The hole is generally filled from 1/3 to 1/2 its depth with the explosive.

The hole is then summed. Stemming consists of filling the remaining 2/3 to 1/2 depth of blast-hole above the last compacted layer of explosive with inert and non-combustible material like powdered clay, rock and, sand. This is also done in installments. Each installment of the stemming material is thoroughly compacted before placing the second layer. The main object of the stemming process is to prevent the escape of the gases produced by the explosion through the hole. They are made to pass to other directions and do the job of breaking the rock by their energy.

Safety Fuse

It is also customary to put the safety fuse for firing at the beginning of stemming operation. In another arrangement, a thin rod is kept inserted in the hole during the stemming process. This rod is removed at the completion of stemming, and the fuse is inserted in its place.

Sometimes stemming is done in layers alternating with explosive layers. This becomes almost necessary in deep holes involving the use of large quantities of an explosive in each shot.

Quarrying Process

We take many things in the material world for granted, not realizing or appreciating their presence or value.  Construction materials that make up the material world around us come into this unconscious, invisible category.  Though you see buildings, roads, footpaths and bridges every day, it’s almost certain that you have never thought about what the materials are, what they are made of, or where they come from. The vast bulk of our built environment is formed from raw materials won from the earth by the extractive industries.  Without the raw materials with which to build houses, hospitals, schools, factories, roads, etc., life would certainly be more basic and less comfortable than we presently experience.

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Sources

civilseek.com/quarrying-of-stones/

theconstructor.org/building/quarrying-of-stones-construction-works/17284/

www.northstonematerials.com/quarrying_process_and_quarry_products#:~:text=Stone%20quarrying%20is%20the%20multistage,macadam%20(bitmac)%20or%20asphalt.