THE DRILLING & BLASTING OF ROCK ENCOUNTEREDIN AN EXCAVATION IS AN ACCEPTED PROCEDURE TO ACCOMPLISH THE EXCAVATEDLIMITS TO BUILD A STRUCTURE.

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1 "r..li 00 :ifm. EXPLOSIVESSPECIALISTS JOHN JOSEPH,Inc. BLASTING CONTHACTORS CONCRETE DEMOLITION EXPLOSIVE FORMING & SIZING OF METALS 695 WESTBROOK ROAD PHONE BLASTING PROCEDrJl1J!:fD, N.J FAX THE DRILLING & BLASTING OF ROCK ENCOUNTEREDIN AN EXCAVATION IS AN ACCEPTED PROCEDURE TO ACCOMPLISH THE EXCAVATEDLIMITS TO BUILD A STRUCTURE. THE UNITED STATES BUREAU OF MINES HAS DONE MUCH RESEARCH ON THE SUBJECT AND HAS ARRIVED AT A, CONTROLLINGCRITERIA THAT IS ACCEPTED AS THE STANDARD. THERE~RE THREE MAIN ADVERSE EFFECTS OF BLASTING. 1. AIRBLAST - MEASURED IN (DB) DECIBELS 2. FLY ROCK - THAT CAN RESULT FROM A POORLY PLANNED SHOT OR UNKNOWN GEOLOGICAL FORMATIONS SUCH AS SEAMS OR VOIDS. 3. GROUNDMOTION- MEASUREDIN (PPV)PEAKPARTICALVELOCITY. 1. AIRBLAST -(DB) SHOULD NOT EXCEED 134. WE TRY TO STAY BELOW 124 DB ON ALL BLASTS. ON RARE OCCASIONSTHE DB'S MAY GO TO 130 IF THERE IS A SEAM IN THE ROCK OR GEOLOGICAL FORMATION IS SUCH THAT FRAGMENTATION ALLOWS SOME ENERGY TO ESCAPE INTO THE AIR. 2. FLY ROCK - CAN BE KEPT TO A MINIMUM BY PLANNING THE BLAST TO ALLOW FOR THE EXPLOSIVE ENERGY TO BE CONFINEDTO THE EXTENT TO BREAK ROCK AND WHEN THIS IS QUESTIONABLE, BLASTING MATS CAN BE PLACED OVER THE AREA BEING BLASTED. 3. GROUND MOTION (PPV) IS MEASURED BY A SEISMOGRAPHAT THE NEAREST STRUCTURE AND SHOULD NOT EXCEED A PPV OF 1.25 IN ANY PLANE (LONGITUDINAL, TRANSVERSE, VERTICAL). WE ATTEMPT TO KEEP ALL SHOTS BELOW.75 PPV. ON OCCASIONS ONE MAY GO CLOSE TO A PPV OF 1. '/. EVERY BLAST IS MONITORED BY A SEISMOGRAPH AND THE RECORDS ARE KEPT WITH THE BLAST LOG. THEREFORE, MANY FACTORS HAVE TO BE TAKEN INTO CONSIDERATION PRlOR TO STARTING.

2 ị B = KEY Burden J = Subdrilling T = S = Stemming Spacing H = Hole Depth - 2 -

3 BORE HOLES ARE DRILLED IN A ROCK AT LOCATIONSSO THAT THE BURDEN (DISTANCE FROM THE NEAREST FREE FACE) AND THE HOLE IS OF SUFFICIENT SIZE TO HOLD TI-IE AMOUNT OF ENERGY PRODUCED FROM THE EXPLOSIVE CHARGE. THE HOLE DIAMETER WILL DETERMINETI-IESIZEAND AMOUNT OF CHARGE THAT CAN BE PLACED IN THE HOLE AND WILL ALSO HAVE TO BE TAKEN INTO CONSIDERATION PRIOR TO DETERMINING THE DRILL PATTERN. TO CONFINE THE ENERGY IN THE ROCK, A STEMMING MATEIUAL IS USED AT THE TOP SECTION OF THE HOLE WI-JICH IS USUALLY 3/8" CRUSHED STONE FOR 2-1/2" HOLES. IT IS OBVIOUS THAT THERE I-IAS TO BE MORE STEMMING IN DEPTH THAN BURDEN ON THE HOLE, OTHERWISE,T1-lEENERGY WILL COME OUT TI-IE TOP WHICH WOULD BE DIFFICULT TO CONTROL. SFACING IS TI-IE DISTANCE BETWEEN ADJACENT BLAST HOLES, MEASUREDPERPENDICULARTO TI-lQ BURDEN.TI.IISIS DETERMINEDBY TI-IE SIZE OF CHARGE, ROCK FORMATION (STRATA) AND AMOUNT OF ROCK BEING FRAGMENTED AND DISPLACED BY EACH CHARGED HOLE. HOLE DEPTH IS DETERMINED BY MANY FACTORS. FIRST RULE OF THUMB COVERS ONLY TI-IERECOMMENDEDMINIMUM WHERE H-D = 2X (B) H-D = HOLE DEPTH IN FEET 13= BURDEN IN FEET WHICH MEANS IF YOU I-IA VE 4' O.I-'BURDEN ON TI-IE HOLE THE MINIMUM DEPTH OF HOLE WOULD I-lAVE TO BE 8' DEEP AND SUBDRILLlNG BECAUSE OF PEAKS OF ROCK BETWEEN DRILL HOLES. SECOND RULE OF THUMB FOR SUBDRILLlNGIS TO DRILL 20% TO 50(YuOF Tl-IE BURDEN ON THE HOLE IF TJJERE IS A NATURAL SEAM 2' BELOW THE BOTTOM OF THE HOLE, THERE IS A POSSIl3!LlTY THAT THE ROCK COULD POSSlBL Y FRACTURE TO THAT DEPTH BUT CANNOT 8E DETERMINED UNTIL EXCAVATION TAKES PLACE. -J-

4 A TYPICAL SHOT WOULD FRAGMENT AS SHOWN IN THIS ILLUSTRATION:,.' Drillingbelow the grade to insure breaking the entire bottom to the grade

5 ALL STATE & LOCAL RI2GULATIONSARE ADHEREDTO ANDA SEISMiC RECORDING OF EACH BLAST SHOT IS TAKEN AT 1'1.112NEAREST STRUCTURE. THE STATE AND LOCAL GOVERNINGDODiESARE NOTlFIED EACH DAY PRlORTO BLASTiNG. AFTER EACH SHOT TI-IEMUCK (BLASTEDROCK) IS EXCAVATED TO DETERMINE IF THE GRADE HAS BEEN ATTAINEDWiTH THE PROCEDURE USED, SOME OF THE MUCK IS PLACED BACK AGAINSTTHE FREE FACE TO HELP CONTROL ANY FRAGMENTS OF ROCK FROM ESCAPiNG PROM THE NEXT BLAST AND TO LOWER THE DB'S (AIRBLAST) WHICHIS ALSO MONITOREDBY THE SEISMOGRAPH. WI-IEN WE ASSESS AN AREA IllA'!' NEEDS BLASTING ALL THESE FACTORS AND OTHERS ARE TAKEN INTO CONSlDERATJON. THETYPEOF ROCKTHAT HAS TO DEBLASTED,WHICHDiCTATESWHAT TYPE AND AMOUNT or ENERGY WILL DE NEI2DEDTO ACIllEYE THE RESULTS THAT ARE DESIRED, AS WELL AS THE PUBliC RELATiONSWITr-INEIGHBORS, OTHER STRUCTURES OR UTlLiTWS ADJACENT OR NEARBY. WEUSUALLYSTARTBYSHOo-fINGTHREETO SIXHOLESONTI-IEFIRST SHOT AND DELAYING EACH HOLE BY 25 MILliSECONDS USING DIRT IF AVAILABLE WITH CABLE BLASTiNG MATS BEING STRATEGICALLYPLACED TO ATTEMPTTO CONTROLTI-IEFRAGMENTEDPIECESTO AN AREA THAT IS SATISFACTORY. THiS METHOD IS REPEATED TO ACCOMPLISHWHATNEEDS TO BE BLASTED. WHAT MOST PEOPLE ASK IS, I-lOW DO YOU KNOW DO YOU HAVE TO PLACE IN THE HOLE? HOW MUCH EXPLOSIVES THEREIS A RULE OFTHUMB IN THIS CALCULATIONWHICH IS WHEN flguringthecubicyardsof ROCK THAT TIlE HOLE WILL FRAGMENT AND DISPLACE. IT WILL TAKE FROM 1.2 LBS, TO J.5 LBS. PER CUBIC YARD TO ACCOMPLISH THIS TASK DEPENDENT ON '['J.18 GEOLOGICAL FORMATiON AND TYPE OF ROCKTHAT HAS TO BE BLASTED, WE USUALLY START WITH 1.4 Ll3S. IF Tl-11::ROCK IS HARD AND DENSE WITH SUFFICIENT BLAST MATS TO CONFINE TI.lE FIRST TRIAL BLAST, THEN CHANGE OR ADJUST WHAT IS NEEDED AS YOU PROGI<-ESS, - 5 -