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. QUARRYING OF STONES: The process of taking out stones from exposed surface of natural rock beds is known as the quarrying. While selecting a quarry site, one should remember that the availability of quantity; desired quality, transportation facilities, cheap local labour, and free from the permanent structures in the vicinity , drainage of rainwater etc.. In case of a quarry, the operations are carried out at ground level (in an exposed condition) whereas in case of mine, the operations are carried out under the ground at greater depths. SELECTION OF A SITE FOR QUARRYING: • Availability of Raw material, Tools, Power, Labour • Space for dumping of refuse material. • Distance of quarry from roads, railways. • Proximity to the transportation facilities. • Easy availability of clean water in sufficient quantity throughout the year. • Economy in quarrying • Blasting material availability • Absence of permanent structures • Geological data regarding rock formations. METHODS OF QUARRYING: The purpose of quarrying is to obtain building stones for various engineering purposes. Depending upon the nature of rocks and the purpose for which stones are needed, quarrying is done by adopting the following methods: Quarrying is carried out by employing hand tools for digging / excavation, Heating, Wedging and Blasting. 1. Digging / excavation: In this method, the stones are merely excavated with the help of suitable hand tools such as Pick axes, Hammers, Spades, Chisels. This method is useful when soft stones occur in the form of small blocks. 2. Heating: In this method, the surface of rock is heated by placing pieces of wood or by piling a heap of fuel over the surface and fired for a few hours. Due to unequal expansion, the upper layer of rock separates out. The detached portion of rock is then removed by suitable hand tools. This method is suitable when the rock formation consists of horizontal layers of shallow depth. Sometimes, intermediate layers are to be separated from the top and bottom layers. In such a case, the intermediate layer is heated and the expansion separates it from the other two. 3. Wedging: This method of quarrying is usually adopted for rocks such as Sandstone, Limestone, Marble, Slate, Laterite etc.. About 10 – 15 cm deep holes, at around 10 cm spacing are made vertically in the rock. Steel Pins and Wedges or Plugs are inserted in them. These plugs are then struck simultaneously with sledge hammer. The rock splits along the lines of least resistance through the holes. 4. Blasting: In this method, the explosives are used to convert rocks into small pieces of stones and the main purpose of quarrying stones by blasting is to loosen large masses of rocks. Explosives such as Gun powder (Blasting powder), Dynamite, (Gelatin), Detonators, Fuse coil etc. are used. The blasting powder and dynamite are commonly used as the explosives. The blasting powder is also known as the Gun Powder which is a mixture of charcoal, salt petre (KNO3) and sulphur. 5. Fuses: It is required to ignite the explosives. It is in the form of a small rope of cotton coated with tar and with a core of continuous thread of fine gun powder. The rate of burning of a good fuse is about 10 mm per second. 6. Gun cotton: The clean cotton is saturated in a mixture of nitric acid and sulphuric acid. It is pressed into blocks or sticks while it is wet. It is as strong as dynamite. But its shattering power is less. 7. Liquid Oxygen: It is oxygen in liquid state. It is stored in a special container. It is comparatively cheap and used for blasting on a large scale for mining operations. PROPERTIES OF BUILDING STONES: Various properties such as Porosity, Permeability, Crushing Strength, Appearance, Durability; Co-efficient of Hardness; Specific gravity; Texture; Toughness Index; Water Absorption; Weathering; Density; Bulk Density; Density Index; Temperature Resistance etc., are to be properly studied before making final selection of any building material for a particular use. Porosity (α ): In simple terms, porosity may be described as the amount of openings ( or ) interstices ( or ) empty spaces present in a rock. However, Porosity may be defined as “the ratio of openings or pores or voids ( Vi ) in the soil/rock to the total volume of the soil / rock ( V ) expressed as percentage”. If α is the porosity, then α = Vi / V where Vi is the volume of inters tices and V is the total volume. Permeability : The permeability of a rock or soil defines its ability to transmit a fluid or water . Permeability depends on the porosity and interconnected pores character of the rock, thus more porous rocks are more permeable too. (not always). Permeability in a rock is measured in darcies ( 1 darcy = 0.987 µ m2 square micrometer ). • Eg: 1.Shales are highly porous but less permeable because of fine grained nature which does not allow water to pass through the rock due to less interconnected pores. • Eg: 2. Vesicular basalts are highly porous but less permeable because the vesicles in them are not interconnected (i.e., the effective porosity is less). Crushing Strength: For a good stone, the crushing strength should be greater than 100 Newton’s / mm2 . Appearance: The stones which are to be used for face work should be decent in appearance and capable of preserving their color uniformly for a long time. It is desirable to prefer light colored stones as compared to dark coloured stones because there are chances of the latter variety to be attacked easily by weathering agents. Durability: A good building stone should be durable. The various factors such as Chemical composition; Resistance to atmospheric conditions etc… influence the durability of a stone. Following are the important atmospheric agencies which affect the durability of a stone. a) Alternate conditions of heat and cold due to differences in temperature b) Alternate conditions of wetness & dryness due to rain and sunshine c) Chemical agencies such as dissolved gases in rain (eg: NOx; SOx ) d) Growth of trees and Creepers in the joints between the stones. e) Wind with high velocity. Texture: A building stone should have compact, fine crystalline nature, free from cavities, cracks, loose material, softness etc.. Toughness Index: In impact test, if the value of toughness index comes below 13, the stone is not tough. If it comes between 13 and 19, the stone is said to be moderately tough. If it exceeds 19, the toughness of stone is said to be high. Water Absorption denotes the ability of the stone/ material to absorb and retain water. It is expressed as % in weight or of the volume of dry material. Ww = M1 – M x 100 where= M1 means mass of saturated material (g) V M means mass of dry material (g) ( mm3 V means volume of material including the pores ) A good stone, the absorption % by weight after 24 hours should not exceed 0.60. If rain water is absorbed by porous stones causing them to crumble hence, the porous stones are not to be recommended for places subjected to rain, moisture, frost Weathering: A building stone should be capable of with standing adverse effects of various atmospheric and external agencies such as rain, frost, wind etc..