NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY CHANGING FROM DECKED-BURN PATTERN TO NON-DECKED BURN PATTERN FOR DEVELOPMENT BLASTING OF DRIVAGE, DECLINES AND RAMPS IN ANUNDERGROUND METAL MINES Author: PARTHA DAS SHARMA, (B.Tech-Hons.) in Mining Engineering (E.mail - sharmapd1@gmail.com) Weblog: http://miningandblasting.wordpress.com/ Abstract: A new Burn-Cut blast pattern has been designed for drives, declines and ramps in underground metal mines, to replace a design (of Decked-Burn with more number of holes), which was giving number of blast failures, such as Under_Blast - difficult to handle. The new Burn-cut design contains less number of blast-holes and Reamer than earlier Decked-Burn-cut. Decked system has been removed to make the charging operation easier. This enables to increase explosives energy in a hole and to reduce stemming length in order to eliminate above blast failures. Moreover, requirement of Detonators is reduced, as Decked system has been abolished. Total explosives quantity has been reduced marginally. Thus, drilling efficiency and cost effectiveness has been achieved. Entire process has been done by changing the original pattern / system in three phases. A. Introduction Excavations of drifts and drives are common features in any metal mining. The specific constrain in driving drivage is, unlike opencast bench blasting, absence of initial free faces.Therefore solid blasting is carried out, for which, Blast Design is most important factor, in order to, create free-faces for successive rows and column of holes.The important factors on which generally progress of drifts and drives depends are: 1.Geology of strata and Rock mass condition2.Appropriate blast design including drilling pattern, quantity and type of explosive, initiation sequence 3.Types of drilling equipment used and length of drilling rod used 4.Dimension of Drives 5.Properties and VOD of Explosives used The cost and time benefit of the excavation are mostly decided by the Rate of Advance. Therefore, it is utmost important to have proper blast design with quality explosives used, in order to achieve maximum rate of advance (Pull) per blast. Burn cut (Parallel Holes with Reamers) blast design is suitable for any dimension of Drift excavation and with proper Explosives, initiation sequences etc., it can give considerable amount of Rate of Advance. The said underground metal mines working for excavation of hard Dolomite based rock; only development work is being carried out. Excavation for Development work such as Declines, Ore Drives NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 2 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ at various levels, Ramps connecting Ore Drives etc., is being done. In underground mines development headings provide; mine access for men & materials, ore & waste transportation, and ventilation paths. Mechanism of creating additional free-faces for Drift blasting - In Drift blasting, explosives are required to perform in a difficult condition, as single free face (in the form of drift face) is available in contrast to bench blasting where at least two free faces exist. Hence, more drilling and explosives are required per unit volume of rock to be fragmented in the case of Drift blasting. A second free face, called cut, is created initially during the blasting process and the efficiency of the blast performance largely depends on the proper development of the cut. The Drift blasting mechanics can be conceptualized in two stages. Initially, a few holes called cut holes are blasted to develop a free face or void or cut along the tunnel axis. This represents a solid blasting condition where no initial free face is available. Once the cut is created, the remaining holes are blasted towards the cut. This stage of blasting is similar to bench blasting but with larger confinement. The results of Drift blasting depend primarily on the efficiency of the cut-hole blasting. The specific constrain in driving drives is, unlike opencast bench blasting, absence of initial free faces. Therefore solid blasting is carried out, for which, Blast Design is most important factor in order to create free-faces for successive rows and column of holes. The factors influencing the development of the cut and the overall blast results are dependent on a host of factors involving rock mass type, blast pattern, Explosives used and the Drift configurations. B. Development work at the Mines: Followings are the major excavation for development work being done at the said underground mines: * Declines with Dimension 5m x 3m, * Ore Drives for all the levels (Dimension -4.5m x 3m). * For connecting the Ore Drives, Ramps are driven (with Dimension 4.5m x 3m) at an interval of 100 to 150m. C. Drilling Equipment: As far as Drilling Equipment for Drifting is concerned, single-boomed Electro-hydraulic jumbo drills are used for Drifting. Parallel holes and Reamer holes can be drilled very easily and rate of penetration is also quite faster. D. Blast Design and Drilling & Blasting for excavation of various development activities at the said UG mines: For face blasting 40mm dia Cartridged Emulsion Explosives (each cartridge length 300mm, contain 390gm explosives) with VOD of about 4000m/s, are used for 45mm dia holes. Drilling length kept mostly 3.4m (or sometime 4.0m). Reamers of Dia 89mm are used. Long Delay Electric Detonators are used for initiation. Face blasting for Declines, Ramps, Ore-Drives and cross-cuts Decked-Burn technique was used, using Long Delay Electric Detonators (as given in Original pattern, Fig. 1). The salient features of the Decked-Burn system were: * The collar portion of the hole was blasted prior to the bottom.* Mid-column decking between the two charges in a hole was kept about 0.5m. NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 3 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ Fig. 1 Original pattern - With above pattern (shown in Fig-1), for 4.5m x 3m face size number of drilling hole (with 3.4m) and Explosives requirements are given below: Faces (with Dimension) Number of Hole drilled Number Holes charged Explosives used in a round (Kg) Detonator used (No.) Stemming Length kept (m) 4.5m X 3m face (with 3.4m Drilling Length) * 46 with 45mm Dia * 4 with Reamer 89mm dia (46+4) 4212050 (In burn holes two detonators were used) 1.3 to 1.6m Fig - 2 NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 4 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ E. Discussion on Decked-Burn Pattern (as shown in Fig 1):* As number of Holes were more, smaller quantity of explosives used per hole (6 to 8cartridges per hole), resulting large stemming length (1.2 to 1.6m); causing a peculiar kind of failure UNDER-BLAST (as shown in Fig 3), in which only inside is blasted and fragmented, whereas outside (Collar) rock appears solid and intact.* Difficult to handle the blasted rock with LHD loaders when there is under_blast. * Difficult to deal with post blast sockets generated, sockets are hollow at the end (Fig 3). * To deal with above kind of failure re-drilling and re-blasting was common; affecting cycle time, cost etc. Fig-3 Fig 4 NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 5 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ F. Searching for solutions:* It was thought to modify the Decked-Burn Pattern by reducing number of Holes, in order to put more quantity of Explosives (7 to 10 cartridges) in individual holes to reduce stemming length (0.6 to 0.8m), to overcome above type of Under-Blast failures. * Also simplification of Explosive Charging procedure was thought of by doing away with the Decked Charging procedure. * For this, New Design of Rectangular Burn (with four Reamers) has been put forth, wherein Deck Charging is eliminated. * Later, Four-Reamers have been reduced to Three-Reamer Burn. G. Solving the problem - Three phased initiative for Re-designing the Drilling Pattern: * In the first phase, one vertical line was reduced in order to reduce number of Holes in the Pattern and the same Decked-Burn was kept intact. * By implementation of one reduced line, 5 Holes were reduced in the pattern, accommodating more number of cartridges in a hole in order to reduce stemming length within 1m. * In the second phase, full Burn was re-designed (Non-Decked) and incorporated in the above reduced-hole pattern. * In this second phase another 4 number of Holes were reduced and also Decked-Charging was removed providing simplification of Explosives charging process and further reducing stemming length to about 0.6 to 0.8m. * In the third phase one reamer was reduced. Instead of four, three reamers were used, without affecting quality of blasts and pull. Fig - 5 NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 6 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ Fig 6 H. DECKED-BURN: Shortcomings (as experienced) * For UG Drives Charging of Explosives is difficult and time-consuming. * Interchanging Delays between inside and outside column of explosives takes place and because of that blast failure occurs. Idea of re-designing and to replace with Non-Decked Burn came up in order to simplify the procedure of charging of explosives and to prevent blast failure due to inadvertent interchange of Delay timings between inside and outside explosives column. I. Phase one - with above pattern (shown in Fig-5), for 4.5m x 3m face size number of drilling hole (with 3.4m) and Explosives requirements are given below: Faces (with Dimension) Number of Hole drilled Number Holes charged Explosives used in a round (Kg) Detonator used (No.) Stemming Length kept (m) 4.5m X 3m face (with 3.4m Drilling Length) * 41 with 45mm Dia * 4 with Reamer 89mm dia (41+4) 37118.545 (In burn holes two detonators were used) 0.8 to 1m NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 7 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ Fig 7 J. Phase two - with above pattern (shown in Fig-7), for 4.5m x 3m face size number of drilling hole (with 3.4m) and Explosives requirements are given below: Faces (with Dimension) Number of Hole drilled Number Holes charged Explosives used in a round (Kg) Detonator used (No.) Stemming Length kept (m) 4.5m X 3m face (with 3.4m Drilling Length) * 37 with 45mm Dia * 4 with Reamer 89mm dia (37+4) 33117.533 (In burn holes two detonators were used) 0.6 to 0.8m NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 8 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ Fig 8 K. Discussion on Trials and Performance of Blasts: * Extensive trial-blast conducted at all the dimensions of drives, i.e., 4.5mx3m, 5mx3m and 5mx4m with 3.4m and 4.0m length of drilling. * No failure as of UNDER-BLAST observed. * No re-blasting was also carried out.* The performance of blasts (Average Pull obtained) is either same or better than the earlier pattern. * It is observed that, with 4m length of drilling, at Ramp-Up pull is better than Ramp-Down. * Side and Top corner sockets observed when there is deviation of Hole. Chances of Hole-deviation with 4m length are more than with 3.4m length. L. Introduction of Third Phase: Reducing one Reamer hole (i.e., using only three reamers with 89mm Dia.): * Later, reduction of one Reamer hole was thought, keeping quantity of explosives and detonator timing same. * Number of trials was taken-up with this three reamer system (89mm Dia.) at both 4.5x3m and 5x3m faces. * All the trial blasts were successful; with similar performance as of four reamers.* Drilling cost and time has been reduced further. NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 9 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ Fig -9 Phase three - with above pattern (shown in Fig-9), for 4.5m x 3m face size number of drilling hole (with 3.4m) and Explosives requirements are given below: Faces (with Dimension) Number of Hole drilled Number Holes charged Explosives used in a round (Kg) Detonator used (No.) Stemming Length kept (m) 4.5m X 3m face (with 3.4m Drilling Length) * 36 with 45mm Dia * 3 with Reamer 89mm dia (36+3) 33117.533 (In burn holes two detonators were used) 0.6 to 0.8m M. Discussion on Advantages of New Pattern:* With new Blast design, blast failure of Under-blast kind and re-blasting is eliminated completely. * As this new blast design does not use Decked charge at the Burn, the number ofDetonators used are considerably less and also gives ease in charging (Charging time is reduced). * As the number of drilled holes is considerably less, the Drilling (Percussion) Time is reduced.* Thus, Cycle time of Drilling and Blasting is reduced considerably Working Efficiency is enhanced.* As drilling efficiency is enhanced (Number of Drilling is reduced) drilling cost also reduced.* This is evident from the fact that, now two full faces are drilled and blasted in one shift, thereby enhancing efficiency. NEW BURN CUT BLAST DESIGN IN DRIVES ENHANCES DRILLING & BLASTING EFFICIENCY WITH ECONOMY - A CASE STUDY 10 Author: Partha Das Sharma,B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com)Weblog: http://miningandblasting.wordpress.com/ * Number of Detonators reduced considerably per blast and also quantity of Explosives (Thus, powder factor, Detonator factor have been improved). * Now this three reamer system has been continued in both 4.5m x 3m and 5m x 3m faces, which further reduced cost and enhanced drilling and blasting efficiency. N. Summary and conclusions: Below tables shows how numbers of holes have been reduced; thus, enhancement of drilling and blasting efficiency and working cost: For face dimension 4.5m X 3m (with 3.4m Drilling Length): Design Changes Number of Hole drilled (45mm + 89mm dia) Number Holes charged Explosives used in a round (Kg) Detonator used (No.) Reduction in Drilling (no. of holes) from previous phase Reduction in Explosives and Detonators quantity from previous phase ExplDet Original (46+4)4212050 Decked- Burn------ Phase - I(41+4)37118.545 Decked-Burn, reduced no. of holes by 5 (45mm) 1.5Kg5 no. Phase - II (37+4)33117.533 Non-Decked Burn, further reduction in no. of holes by 4 (45mm) 1.0 kg12 no. Phase - III (36+3)33117.533 Non-Decked Burn, further reduction in no. of holes by 2 (One 45mm and one 89mm dia. Reaming hole) ------ Final reductions from Original pattern 11 no. of holes (10 of 45mm and 1 of 89mm dia) 2.5 kg17 no. Note: Average Time taken for drilling a hole of 3.4m length by Jumbo drill is 2.5min. Overall 20 to 22% of drilling time and cost have been saved. Similarly, Charging time has also reduced as Decked-Burn system eliminated. As number of drilling holes have been reduced considerably, the percussion time and drilling meterage has been saved. Cost of drill Bits also saved considerably. Moreover, total 2.5kg of explosives and 17 numbers of Electric Delay Detonators have been saved thus, reducing costs. Similar advantages obtained for 5m x 3m faces with 3.4m drilling and also with 4m drilling at 4.5m x 3m faces. Upon obtaining satisfactory performance result, enhancement of efficienciy and eliminating blast failure such as Under_Blast etc.; the new blast pattern has been fully incorporated for all the development section of the said underground mine. Disclaimer: Views expressed in the article are solely of the authors own and do not necessarily belong to any of the Company or institution.