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CLOSE THIS BOOKSpecial Public Works Programmes - SPWP - Stone Paving-Blocks - Quarrying, Cutting and Dressing (ILO - UNDP, 1992, 60 p.)
2. QUARRYING
VIEW THE DOCUMENTQuarrying methods
VIEW THE DOCUMENTQuarrying using a crowbar
VIEW THE DOCUMENTChannelling
VIEW THE DOCUMENTMaking wedge-holes
VIEW THE DOCUMENTQuarry wedges
VIEW THE DOCUMENTCutting a block with wedges and a sledgehammer
VIEW THE DOCUMENTPlug and feathers
VIEW THE DOCUMENTQuarry equipment and tools
VIEW THE DOCUMENTUse of explosives in stone quarrying
VIEW THE DOCUMENTBlock-splitting using black powder
VIEW THE DOCUMENTCalmmite

Special Public Works Programmes - SPWP - Stone Paving-Blocks - Quarrying, Cutting and Dressing (ILO - UNDP, 1992, 60 p.)

2. QUARRYING

Quarrying methods

Once the quarry has been sited, the environmental restoration plan agreed, and the preliminary clearing work completed, the method of quarrying the rock is chosen.

Depending on the type of deposit encountered, whether granite in the form of boulders or in benches from several centimetres to several metres high, the quarrying method chosen will involve the use of a crowbar, quarrying wedges, plugs and feathers, explosives or calmmite (1) to detach blocks of rock from the solid rock mass.

(1) See page 25

Primary cutting is the process by which a fracture is created in the rock mass to detach a block, or in a block of rock to cleave it, by successive breaks, into blocks of manageable dimensions.

The size to which blocks must be cut will thus be determined by the handling system used. In determining a block's dimensions, it is important to relate it to the size of the finished product (paving-blocks or curbstones) which will be made from the block.

If pavement curbstones 100 cm long and with a 20 × 20 cm section are to be produced, one should obtain an initial block of multiple dimensions to those of the curbstones/edging blocks (adding a small margin to allow for material lost in dressing).

For example, after the first cutting stage, the block could measure 105 × 63 × 42 or 105 × 85 × 21 cm.


Figure

Granite block from which curbstones measuring 100 × 20 × 20 cm are to be produced.

It will be possible to cut six curbstones from this block with a minimum of waste.

Quarrying using a crowbar

This method can be employed in a shallow bed of granite where sufficiently wide cracks criss-cross the rock.

The only tool needed is a crowbar. This is a hardened steel bar of hexagonal or round section, 34mm in diameter and about 1800 mm in length.

One end is forged into a four-sided point, the other flattened. Depending on the weight of block to be handled, one or more quarry-workers will be required.


Crowbar

Safety:

a) A crowbar left lying on the ground can easily be tripped over. When not in use, leave it in an upright position where it is easily visible.

b) Safety shoes, gloves and protective goggles must be worn on-site by all workers.

The crowbar can be used as a lever by inserting its point into natural chinks between blocks. The quarry-worker wedges the bar against the edge of another block and, putting his full weight on the bar, moves the block. The principle of a lever is to multiply force severalfold.


Figure

Once the block is too far removed from the original point of leverage of the crowbar, chocks are used to create another leverage point.


Figure

The crowbar may also be moved laterally to steer the block. The operation is continued until the block is sufficiently free to be loaded onto a two-wheel trolley, or hand truck (see page 28) or split into smaller blocks.

In cases where the granite bench is not fractured sufficiently to allow a crowbar to be used, other methods can be employed. Quarrying wedges, plugs and feathers, explosives, or calmmite can be used.

Channelling

Whichever of these methods is decided upon, the first operation will remain the same: the marking of a groove along the cutting-line. The purpose of this 1 - 2 cm groove is to guide the fracture along which the block will be split.


Grooving-chisel

Making the cutting-line groove by hand

The groove can be made manually using a grooving-chisel and club-hammer, or with a pneumatic drill equipped with a chisel end.

Safety:

The wearing of safety goggles, shoes and gloves must be enforced and continuously supervised.


Figure


Tungsten tipped chisel ends

A chisel end is a tool which can be fitted to a pneumatic hammer drill.


Channelling using a pneumatic hammer drill.

Safety:

When a pneumatic drill is used, ear protection is as important as shoes, gloves and goggles. The noise level of quarry operations is great enough to permanently damage hearing if no protection is used.

Making wedge-holes

If working manually, the tools required are a grooving-chisel and club-hammer. The operation may, however, be mechanised using a pneumatic hammer drill and compressor.


Making wedge-holes manually

Safety:

Grooving-chisels which are not in use must be carefully put to one side as they can easily roll under someone's feet and make them fall.

Whichever tools are used to make these holes, be they grooving-chisel and club-hammer or pneumatic tools, two small holes are first made to mark the extremities of the wedge-hole.


Figure

The rock is removed between these two small holes and the wedge-hole is then made by pivoting the tool until the required depth is reached.

Wedge-holes are spaced 15-20 cm apart along the entire length of the groove.


Figure

The base of the hole is enlarged by repeatedly moving the grooving chisel to and fro.


Enlarging the base of the hole.

Quarry wedges

Quarry wedges are pieces of metal, around 70 mm long and 40 mm wide at their widest part.


Figure

They are placed in the wedge-holes.

The wedge presses against the sides of the hole. The hole must be deep enough so that, when struck with the sledgehammer, the wedge does not touch the bottom of the hole.


Figure


Figure

The wedge is touching the bottom of the hole. When struck, it will bounce out of the hole as it will be unable to go in any further.

Note the form of the wedge-hole in the drawing below.


Figure

Safety:

A wedge may fly out of its hole. A safety area of 5 metre radius around workers using a sledgehammer must be respected.

Cutting a block with wedges and a sledgehammer

Wedges are hit into place using a club-hammer. They are then hit in succession using a 5 kg sledgehammer until the pressure exerted on the block is such that it breaks away from the rock mass.

If the height of the block makes it necessary, the break can be guided vertically by placing wedges along the sides of the block as well.


Figure


a. Cutting a block with wedges and a sledgehammer


b. Cutting a block with wedges and a sledgehammer

Safety:

Hammer heads must be tightly secured to their handles. A 5 kg sledgehammer head flying of its handle can seriously injure anyone standing nearby.

Plug and feathers

A set of plug and feathers consists of three parts: a central, sharply tapered wedge known as the plug, which bears on the other two parts which are the feathers.

The lower part of the feathers is thicker to fit against the tapered edge of the plug.

This method of splitting stones, used for hard rocks such as granite, requires the use of a pneumatic rock drill, compressor and drill bit for making the holes.


Figure

The usual size of plug and feathers for granite is 30 mm diameter and 40 cm in length. They are placed in 50 cm-deep holes, made with a 34 mm diameter drill bit. These holes are made at 30 cm intervals along the previously marked groove.


Cross section of stone block

Safety:

Wearing ear-protectors provides effective protection against noise. Without ear protection, hearing can be irreparably damaged by the operating noise levels of pneumatic rock drills.

With the double striking and revolving action provided by the rock drill, the drill bit drills into granite. Rock dust is blown out of the hole by compressed air which is channelled to the end of the drill bit.


Drill bit

Safety:

An air-filtering mask prevents workers breathing in the fine rock dust present in the air due to drilling. Inhaled siliceous granite dust causes a lung disease known as silicosis.

When all the plugs and feathers are in place, they are struck in succession with a sledgehammer. In so doing, lateral pressure is exerted on the complete length of the feathers, to a depth of 40 cm into the stone. This is what distinguishes the plug and feathers from simple quarry wedges.


Figure

Safety:

The immediate work-area should be regularly cleared of all stone waste, stone blocks and tools which are not in use and which could obstruct workers or cause them to fall. One worker should be appointed on a permanent basis to the task of keeping the worksite clear.

Quarry equipment and tools

Item

Weight

Indicative price


Compressor 30 hp diesel engine, output 2.1 m3/minute

600kg

11,700 $


Compressor 30 hp diesel engine, output 2.7 m3/minute

800kg

13,500$


Rock drill (see photo page 20)

18kg

1,100$


Drill bit 037 mm, length 800 mm

3kg

100$

Drill bit 042 mm, length 800 mm

3kg

120$

Hammer drill (see photo page 20)

10kg

850$


Semi-finished rough-forged tool (for above hammer drill)

1 kg

20$

Carbide chisel end

0.5kg

50$

Plug and feathers 030 mm, length 400 mm (see photo page 20)

1.5kg

35$


Ear protectors

0.24 kg

35$

Prices are obtained in France and converted into US$ at an exchange rate of US$ = FF6. Please regard prices as indicative only.


Compressor providing air for a hammer drill


Hammer drill


Plug and feathers ¢30 mm, length 400 mm.


Rock drill with drill bit ¢34 mm, length 800 mm

Use of explosives in stone quarrying

Mention is made here only of the main principles of the use of explosives. Explosives must be handled only by workers who have undergone specific training to obtain a certificate as blasting officers and who have a thorough knowledge of all safety rules regarding the transport, storage and use of explosives.

An explosive is a material which, upon disintegration, produces a shock followed by the release of a great quantity of gas. The shock creates a crack in the rock and the gas, under pressure, escapes into the crack which widens under the effect of the blast thus produced.

So as not to destroy the block of stone, a deflagrating explosive, which decomposes slowly, is used, such as black powder (a mixture of ground charcoal, sulphur and saltpetre) with a shock-wave propagation rate of 300 m/second.

Do not use explosives of the following types:

a) nitroglycerine (A gum)
b) "N", based on ammonium nitrate
c) "O", based on sodium chlorate

The above are detonating explosives with a shock-wave propagation rate after explosion of 2,000 to 8,000 m/second. They have a shattering effect and produce a considerable disintegration of the rock mass, and also create numerous cracks which render the material unfit for dressing. Such explosives are therefore to be avoided in quarrying of stone blocks.

Block-splitting using black powder

First, a groove (along which the rock will be split) is made, following the rock's cleavage (direction of cracks).

Next, blasting holes are made along the groove, either using the hammer action of a rock drill (fitted with a chisel end) or a crowbar if the rock is soft (sandstone or limestone).


Boring with a 2-metre crowbar

Average productivity rate in sandstone: 1.5 work-days per linear metre.

Boring in soft rock

In hand drilling soft rock such as sandstone, water is used to free the hole of rock dust and thereby facilitate boring.


Rubber ring to prevent water from splashing out whilst boring.

The number of holes depends on the size of the rock mass to be split Next explosive cartridges are placed at the bottom of the holes. The number of cartridges per hole is determined by the strength required of the explosion, which in turn also depends on the size of the block to be split.


Blasting preparation (the holes are sealed while waiting for the explosive charges to be put in place)


Figure

Black powder is primed using a slow fuse which transmits a flame at the rate of 1 metre in 90 seconds. Once the primed cartridges are in place in the holes, the holes are packed with clay or sand.

The fuse is lit by the certified blasting officer only after all quarry workers have been guided to a safe location.

The shock wave caused by the explosion will be guided by the groove.

Safety:

Use of explosives is dangerous. This means that safety precautions must be taken.

All stipulations contained in national legislation and regulations, as well as recognised guidelines on the use of explosives, must be respected. Rules regarding the transport, storage and use of explosives and detonators aim at protecting people and property against bodily or material harm. Only holders of blasting certificates can be authorised to handle and use explosives.

Calmmite

A new product, Calmmite, can sometimes serve as an alternative to explosives. Calmmite sticks are soaked in water before being placed in holes drilled in the rock. With hydration, Calmmite expands with great strength, breaking the rock after 12 - 36 hours without explosion. Although still relatively expensive, Calmmite is often an appropriate quarrying tool, especially in fragile mountain environments prone to landslides and erosion. Like explosives, Calmmite must be handled with care.

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