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1 <br />The second stage is blasting damage reduction Ls to delimit the :neat of tack fracture and cw take the <br />fallowing form: <br />o buffer blasting <br />o smooth blasting <br />' o pre-sp[tting <br />Buffer blasting involves limiting the amount of explosive energy per unit area of final face by <br />' decreasing burden and spadag and explosive charge per hole but main"~ the same overall powder <br />factor and blasting the holes is normal sequence. <br />Smooth blasting iavolvu spGttiag along the exczvarioa boundary with closely spaced holes which are <br />' loaded with decoupled explosives, that is the eplosives do not fill :he hole. The holes arc then blasted <br />aher the main blast and, if possible, simultaneously. <br />' Pre-splitting is similar to smooth blasting except that the holes aze blasted before the main olu[ and <br />simuka¢eously. <br />t In order to achieve the smooth wall required is the footwall'Buffer Blasting" is the most practics! <br />alteraadve. Beach bhutiag can employ either of the following methods: <br />o Buffer Blasting <br />' Buffer blaring is possibly the simples[ and most effective method of bias[ wntroL It involves <br />modifieztioas of the last rows of the main bLu[ pattern (see Fgure 1). <br />' Vfodifiezcioas are limited to reduced burden spacing and explosive loads The goal is to reduce ground <br />shock to [he final wall. The method is usually employed in conjunction with some other control <br />blaring technique. Buffer blas[i¢g should only be used by itself when the ground is fairly comnetea[. <br />It may produce minor nest fracturing or barsbzeak but the damage is less than that producad by [he <br />main producrioa blast if ao control blasting would be used- <br />' o Geaezal Guidelines <br />Hole siu and depth should be the same u for holes is the production blur. Depth of subgrnde should <br />be 7 to 10 times the hole diameter to eliminate hard toe and to promote drainage for haul roads. <br />Hales posirio¢ed duectly above or near the nest of as underlying berm should not have any subgrade <br />to reduce Qest fractnring. <br />' Pattern design is u follows: <br />o reduce powder factor is buffer row by half of the main production blast. <br />' o burden and spaaag far buffer row should be OS to 0.8 times that of the adjacent row, hole <br />spadag = L25 z burden <br />' o buffer row is to be fired after the produmo¢ holes with az leut a 15 miIlisec delay <br />o depth of collar should be 12 Marge diameters. <br />Smooth BLaiiag <br />' Smooth blasting and pre-splitting rely for their effect on the fan that sacks will form preferemdally <br />between closely spaced hales before the other radial aaclcs have eueaded very faz into the rock mass: <br /> <br />1 <br />