Quarrying, the primary process involved in acquiring natural stone, refers to the extraction of valuable stone from exposed areas of natural rock, known as quarries. These quarries serve as the source for obtaining sought-after stones. When selecting an optimal quarry site, several critical factors come into play: the availability of a sufficient quantity of high-quality stone, convenient transportation facilities, access to cost-effective local labor, considerations regarding rainwater drainage, proximity to essential and permanent structures, and a designated area for waste disposal.
Stone Quarrying Tools
Some of the quarrying tools shown in Fig below are wedge, pin, hammer, dipper or scraping spoon, tamping bar, priming needle, jumper, borer, claying iron, crow bar.
A wedge is used to split the stone along a line of weakness. A pin is used to drill a small hole in the stone. A hammer is used to strike the pin and drive it into the stone. A dipper or scraping spoon is used to remove the dust of crushed stone from blast holes. A tamping bar is used to ram or tamp the material while refilling blast holes. A priming needle is used to maintain the hole when tamping is being done. A jumper is used to make blast holes. A borer is used to drill a hole to the required depth. A claying iron is used to cut and remove clay. A crow bar is used to move large stones.
Methods of Quarrying
Rocks suitable for the production of stone materials are referred to as valuable minerals, and the processes involved in acquiring these minerals are known as mining. During mining operations, the voids created are termed as excavations, and the acquired deposits become quarries. The primary objective of quarrying is to procure stones for various engineering purposes. While understanding various quarrying methods is essential, it alone does not significantly enhance the ability to select or specify a stone for construction projects. Depending on the characteristics and surface of rocks, as well as the intended purpose of the stones, quarrying methods may involve excavation, wedging, heating, or blasting.
Excavating
Excavation involves the retrieval of stones hidden beneath the earth or within loose overburden. This process typically employs a variety of tools such as pickaxes, crowbars, chisels, hammers, and similar implements. Workers use these tools to carefully extract the stones from their embedded positions, often requiring meticulous attention to avoid damaging the stones during the extraction process. Excavation methods may vary based on the size, depth, and nature of the stone deposits, with techniques adapted to ensure the safe and effective retrieval of the desired stones.
Wedging
This method of quarrying is particularly suitable for soft and stratified rocks such as sandstone, limestone, laterite, marble, and slate. The process involves drilling holes about 10–15 cm deep, spaced roughly 10 cm apart, vertically into the rock surface. Steel pins, along with wedges or plugs (conical and flat), are inserted into these holes. The arrangement using plugs and feathers tends to be more effective. Using a sledgehammer, these plugs are simultaneously struck, causing the rock slab to split along the lines of least resistance within the holes.
For softer rocks, dry wooden pegs are hammered into the holes, followed by the pouring of water. As the pegs absorb moisture and expand, they exert pressure, leading the rocks to crack along the hole lines. Subsequently, the wedges are positioned along the exposed face of the rock, precisely on the plane of cleavage (the joint between two layers), and hammered. This process enables the detachment of the slab, which can then be extracted with the assistance of crowbars and rollers.
This method results in minimal wastage and allows for the extraction of slabs in the desired size and shape.
Heating
Heating is an effective method for quarrying small, thin, and uniform blocks of stone from rocks like granite and gneiss. This technique involves piling and igniting a heap of fuel on a specific area of the rock surface. The uneven expansion of consecutive layers of rock due to the heat causes them to separate. The loosened rock sections are then broken into pieces of the desired size, which are subsequently removed using pickaxes and crowbars. The resulting stone blocks are well-suited for coarse rubble masonry.
At times, it’s necessary to separate intermediate layers from the top and bottom layers. In such cases, an electric heating method is employed specifically on the intermediate layer, causing it to expand and separate from the other two layers.
Blasting
Various explosives, including blasting powder, blasting cotton, dynamite, and cordite, are utilized in quarrying operations. These operations encompass several stages: boring, charging, tamping, and firing.
To begin, holes are drilled or bored into the rock to be dislodged. For vertical holes, a jumper is used, while inclined or horizontal holes require boring bars. The drilling process involves one person holding the jumper or boring bar in position while another strikes it up and down, with simultaneous rotation. Water is regularly poured into the hole during drilling to soften the rock and aid in the process. Any mud generated during drilling is removed by scraping. In cases of hard rocks, machine drilling replaces manual drilling.
After drying the holes completely, the necessary amount of explosive charge is placed within them. If moisture is detected, a drying process using a rag tied to a scraper is conducted to ensure water-tightness inside the hole.
Following this, a greased priming needle, slightly protruding from the hole, is inserted and packed with damp clay or stone dust in layers, using a tamping rod to secure it. The priming needle is rotated during tamping to maintain its looseness within the hole. Subsequently, a Bickford fuse, a cotton rope coated with tar, is placed in contact with the needle. Upon withdrawal, 60 to 75 percent of the void left by the needle’s removal is filled with gunpowder. Blasting powder and cordite are ignited using a fuse, while gun cotton and dynamite are detonated.
Safety measures during blasting are crucial to avoid accidents. These include ensuring that blasting occurs neither late in the evening nor early in the morning, publicly announcing blasting hours, marking a 200-meter radius danger zone with red flags, and providing first aid. Additionally, keeping records of charges fired, handling explosives cautiously, and ensuring proper storage in specialized magazines away from residential areas, among other precautions, are essential.
The quantity of explosive required varies based on factors like the explosive strength, method of blasting, bore hole characteristics, and the rock type.
An approximate estimation of explosive quantity needed can be made using the formula
A =
L2/0.008
where, A represents the quantity of gunpowder or dynamite in grams,
L stands for the length of the line of least resistance in meters.
