CHAPTER 4

BLAST DESIGN

4.0. BLASTING DESIGN. The first step indesigning the cut is to design the blasting such that theblast effects are controlled to suit the requirements ofthe operation. Knowledge of mathematical formulaswill provide ease in designing a blast that will be safeas well as effective. A common way of designing ablast is using the Powder Factor method.

ling minus stemming.

f. Determine pounds of explosive/foot ofpowder column. Use Chart C. or, use formula:Diameter squared x 0.34 x specific gravity ofexplosive. Note: Blasters must la1ow the explosivedensities of the explosive they are using to use thischart C.

4.1. POWDER FACTOR. The powder Factor is acommon tenn used frequently in blasting operationsand means simply the number of pounds of explosivesnecessary to break a certain quantity of rock. Forexample, if a blaster uses 1,000 pounds to break 1,000cubic yard of rock, his Powder Factor is 1 pound percubic yard. The Powder Factor tenD is very generaland does not define the distribution of the explosive inthe hole, the pattern, hole size or face height andsubdrilling, Normally, the subdrilling is not included inthe yardage or tonnage figure because it is not payrock.

g. Detennine total load for the borehole.Powder column times step (f) (pounds of explosive perfoot of powder column). Find the pattern ~ boreholeload can break.

h. Divide the total load by the borehole depili.This will equal ilie number of cubic yards per foot ofborehole that can be broken.

i. Determine the approximate square patternfrom Chart C or multiply the number obtained in step(h) by 27 and take the square root of this to determinethe square pattern. This procedure was written for freerunning explosives. You must also use the chart on pg482-483 of the Dupont Blasters Handbook.

4.2. POWDER FACTOR PROCEDURES.tem1ine total explosive per hole as follows:

De-

a. Detennine borehole diameter.j. Adjust to a rectangular pattern of the same

total cubic yards.b. Determine borehole depth.

k. Adjust stemming and subdrilling if it appearsnecessary .

c. Detern1ine Stemming (24 x borehole di-ameter). Divide by 12 to get the number of feet ofstemming.

NOTE:FOR POWDER FACTOR OrnER 1HAN 1POUND PER CUBIC YARD, DIVIDE mENUMBER OF CUBIC YARDS OBTAINED INS1EP (h) BY THE POWDER FACTORDESIRED.

d. Detem1ine sub drilling (1/3 x stemming).

e. Detennine powder column (amount of hole tobe loaded). Borehole depth plus subdril-

4.3. DRYING BOREHOLES. Some boreholesmay contain water. Explosive cartridges can be

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Driller fills out the Drilling log (Appendix A) showingactual depth, cracks, seams and voids. A diagram ofthe pattern and bench face is drawn at the bottom of thepage. The Head Blaster will use this form to showexplosive location in the hole, stemming, deck loading,etc. On the shot diagram the trunklines, MS connectorsand initiating devices will be drawn in. The tool list isfor tools used in the blasting operation. Chronologicaltime is kept for the blast.

distance from the next hole and should be delayed toprevent backbreak or overbreak into the next bench.This delay may be accomplished with a delay cap or thehole(s) may be primed and initiated separately after theothers.

-Single-Row Delay Within Row. This patternrequires more holes per width of face but gives theadvantages of better fragmentation, less ground and airvibrations from the blast, and controlled throw of thebroken material. The holes are initiated in sequencestarting at the center and moving out in both directionsat the same time in 0.025 second intervals with theexception of the comer hole which may be initiatedseparately at a longer delay as mentioned above. Thisinitiation pattern will result in throw to the center. Ifthe holes were to be initiated starting at the right andproceeding to the left, the throw would be to the rightside of the face.

4.7.2. Loading Record. The Quarry LoadingRecord (Appendix B) is a written description of theexplosives and other pertinent infonnation for eachhole. This record is filled out by the Head Blaster.

4.7.3. Shot Record. The Quarry Shot Record andExplosive Inventory (Appendix C) is a record ofexplosives and general information. It provides futurereference for information regarding a shot. The QuarryShot Record and Explosive Inventory is filled out bythe Head Blaster.

4.7.4. Explosive Log. The Blaster's Explosive Log(Appendix D) is a prior planning document andchecklist used by the Head Blaster to manage the blastproperly. A Head Blaster should not rely on memory toconduct any blasting operations. A written plan of theblast needs to be in the blaster's possession. TheBlaster's Explosive Log provides that plan.

4.8. DRILLING PATTERNS. After the desiredwidth and depth of cut have been determined, thedrilling pattern may be selected. The patterns discussedin the following paragraphs are pertinent to bothvertical and inclined holes. Selection of a drillingpattern should include consideration of the method ofblast initiation to be used (delay or simultaneous).

4.8.2. Multiple Row Patterns. Multiple rowpatterns are of three types, staggered, rectangular, andsquare, and generally require the use of delay caps orother delay devices.

.Staggered Pattern. The staggered pattern isused for simultaneous initiation of holes within a rowand delays between rows. Throw is to the front with asmall portion at the end of the bench being thrown offto one side. The staggered pattern may be used forsimultaneous initiation of an entire layout consisting ofnot more than two rows of holes.

.Rectangular Pattern. Similar to the staggeredpattern in spacing between rows and holes. The mainadvantage of this pattern is that it simplifies themaintenance of square comers on the bench byinitiation of a delayed charge at the end of the row.

.Square Pattern. With the square pattern,throw can be directed toward the center or to the sideby delayed initiation within rows. The volume ofmaterial obtained per hole using this pattern is nearlyequal to that obtained in using the staggered pattern.The reason for this is that the spacing between rows isgreater. The use of this pattern allows the maintenanceof square corners with much greater ease than thestaggered pattern.

Single Row Pattern.4.8.1.

.Simultaneous Initiation. This pattern is mostdesirable from the standpoint of maximum breakageand displacement per hole drilled because it allows fora greater spacing. Normally, there will be two nearlyvertical free faces, the front and one side. The holenearest the open side is drilled one burden distancefrom each face. Comer holes are drilled one burden

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