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INTRODUCTION Dimensional stones, such as, granite, marble, sandstone and splittable limestone are used for their aesthetic and attractive characteristics, namely colour, texture, polish, etc. The world stone production is over 60 Mt/year and is growing at an annual rate ofabout 5%. India is the leading producers, users and exporters of stones.

TECHNOLOGIES CURRENTLY USED IN QUARRYING ACTIVITY Explosive splitting (perforation + explosive) 1.granite.2.marble3.sandstone-otherstones Wedge shearing Flame jet 1.Granite Line drilling or slot drilling 1.granite2.marble Water jet 1.Granite 2.sandstone

COST OF SPLITTING Where. 1.Flame jet 2.Wire saw 3.Explosives 4.Slot drill

FRACTURE CONTROL TECHNIQUES IN ROCK BLASTING During conventional blasting micro cracks and macro cracks are developed in the rock. The process of micro crack propagation is not a single crack but an envelope of micro cracks that propagate. But macro crack development in desired direction is required for block separation and splitting but there is need to reduce micro crack development in the extracted block and remaining rock. This type is referred as controlled fracture growth which has an important role in dimension stone mining.

FRACTURE ALONG GUIDED PATH The procedures commonly employed in dimensional stone blasting are: alternate charged and dummy holes, a line of dummy holes, and notching the holes to initiate the cracks. A dummy hole between two charged holes serves to reduce fracture in the guide plane. The technique of blast hole notching is effective in dimensional stone quarrying.

FRACTURE ALONG GUIDED PATH It allows a significant increase of blast hole spacing so that the drilling quantity, explosive loads and also the risk of damage to the rock can be reduced. The notched drilling increases the drilling cost by 20% to 30%, but this cost is approximately balanced by the reduction of drilling length and explosive consumption. Additional benefits to the overall economy, improves the quality of the cut face and reduces rock mass damage, so that a larger amount of stone is recoverable.

FRACTURE CONTROL BY EXPLOSIVES The control of the fracture plane has been accomplished by using a 'slotted cartridge' (a specially designed cartridge with longitudinal slotted shell made of hard plastic pipes) that permits control of the initiation, propagation and arrest of cracks to produce the required fracture plane as specified. Successful results obtained by applying this slotted cartridge in the field have verified the effectiveness of this control action.

FRACTURE CONTROL BY DECOUPLING Blast hole pressure and damage can be reduced by decoupling of charge. Charges are decoupled when they do not touch the blast hole wall. The ratio of the charge radius is a measure of the decoupling of a charge. When, a decoupled charge is surrounded by water, its effective strength increases upon detonation.

EXPERIMENTATION The principle objective of experimental work was to develop cracks in the rock so as to dislodge it from the surrounding rock without causing damage to extract block or to the remaining rock. The experimental work with detonating cord in circular hole in conventional manner, detonating cord with PVC pipe, detonating cord with cardboard/plastic liner and notching with cardboard were devised whose details are shown in figures given below.

LOADING OF EXPLOSIVES

LOADING OF EXPLOSIVES

VARIATION OF EXPLOSIVE ENERGY Initially different tests were carried out with detonating cord containing 10g/m, 20g/m, 30g/m, 40g/m and 50g/m PETN, special gelatine (NG-based) and ammonium nitrate and fuel oil (ANFO) to quantify the damage. Based on the study, comparison was carried out with detonating cord, special gelatine (NG-based) and ANFO. As a result, special gelatine and ANFO were not used and detonating cord was found suitable but sometimes creates damage to the rock.

BLAST HOLE NOTCHING IN DESIRED CRACK DIRECTION For the notching of the holes, a jackhammer hole with 51mm dia bit was used after stopping its rotation. With the help of vertical motion of jackhammer notching of 34 mm dia circular holes were drilled in the field. With the help of 51-mm dia the notching length in 34-mm dia circular hole was 8.5-mm on both sides of the hole. The notching was made diametrically up to a depth of 0.10m- 0.25m. The notching was found very helpful in guiding the crack in desired direction.

BLAST HOLE NOTCHING IN DESIRED CRACK DIRECTION Notching in the blast hole increases the spacing and cardboard lining protects the damage to the remaining rock as well as in the extracted block. It has also increased the hole spacing and reduced cost of drilling.

BLAST HOLE LINING The metal pipe of 30-mm outer dia and one mm wall thickness was cut along the length and used in the blast hole to protect the damage to the remaining rock. With this lining, damage was completely protected but pipe was bent and could not be reused. The poly-vinyl chloride (PVC) pipe of 30-mm outer dia and 2-mm wall thickness was also tried in the form of blast hole lining, but it also got damaged completely at the bottom and cracks developed along the length of the pipe. Therefore, a cheap method is required to protect the damage to the remaining rock/block. Thereafter cardboard and plastic liners were tried to protect the damages.

COMPARATIVE STUDY OF COST OF VARIOUS DIMENSIONAL STONE EXTRACTION TECHNIQUES

CONCLUSION Detonating cord without protecting devices creates crack in the desired direction but some fracturing in the rock also occurs occasionally. Hence, protecting devices are used to protect the unwanted damage. By using notched hole, the spacing of holes increases and the quantity of extracted block also increases per metre of drilling. By this technique excellent crack in the desired direction is achieved with very little fracturing in other directions. This small amount of fracturing can be fully controlled by using card board/plastic liner.

CONCLUSION No visible cracks are appeared when cardboard or plastic liner is used. In holes where notching and lining is used no damage is occurred. Dimensional stones can be extracted economically with detonating cord of 30g/m-50g/m at hole spacing of 0.30m-0.50m. Further by using cardboard /plastic liner free of cost, damage free block can be extracted.