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tv $ :iii ri;:: imi,i: ii: ,: _;::' ,:,:l:,,:irJl:; :::","/jt'i-t j,:_'r:::': :',:::::1::: _1 :'f-'i;::![' ,!Hi ': 2 2,;iC,,; 1:'::;;;:i:n+:1.75ft/1b 1/3wehavenomeansofestimatingc/m (seeFigure6anddiscussioninSection6.1).Thus,no comparisoncanbemadebetweentheempiricalandGurneymethods. 3Inanycase,thef1yrockrangeundertheseconditions(S/W 1/> 1.75).isexpectedtobesmall. 43 A s s U ~ d* L* 2 ** VV v LS/W13 0 m00 m*** . Rock. (ft/1b 1/3) (m/sec)(m)c/m X10 4 (m/sec)(m/sec)(m) Granite1.75351255.461320a/36135 Granite1.5391556.061529a / 39156 Granite 1 . 0 ~542979.322666a /52272 Granite0.59490021. 66460a / 83708 Sandstone1.620413.72368b/ 1938 Sandstone1.324594.20477b/ 2249 Sandstone1.030.925.29724b/ 2774 Sandstone0.7421808.211385b/ 37141 Sandstone0.556320.17.03377b/ 58344 * FroIT\Figure7 ** FromEquation(2 ) * ** FromFigure6 a/FromEquation .Lobs PowderFactor 3MineRockBenchTopVerticalFaoe(feet)Ibs/yd PossibleCause ConklinQuarryLimestone'\1430'\123012000.45Overloadedholes(?) a/SibleyQuarryLimestonesmall"'1254750.9Undetermined RobertaQuarryLimestone'\1150"'1351600'\11.7Undetermined FallingSpringsLimestone'\1790'\127020000.7max.Fissures;alsomar-Quarryginalstemming OkalonaQuarryLimestonea/a/1600 a/Overloadedholes OglesbyQuarryLimestone a/a/2500 a/ Undetermined dLatahQuarryTrapRock '\IOc/ 30-120 b/3300 ~ 6 8 undetermined / ~0'1 Mine0Taconite"'1430avg.'\1300max.45001.2avg.Insufficientstemming BerkelyPitPorphyry '\IOc/ a/840a/Someholesmayhave partiallycavedin; consequentlyexplosiveloadcouldhave risenmuchhigher thanplanned. MineASandstone'\1235"'20'\18000.53Fissures a/Insufficientinformationto.compute. b/Lowervaluecomputedwithgraniteconstants;highervaluecomputedwithlimestoneconstants. c/Accordingtoshotconditionsgivenir.thereport. d/Flyrockmusthaveoriginatedatbenchtopsinceobservedflighttimeismuchtoolongforflyrock fromverticalface. Table9"WILD"FLYROCK chargeandburdendoesnotalterflyrockvelocity.Thissuggests thattoafirstapproximationtheflyrockvelocityproducedbya givenexplosiveloadforboreholeswithandwithoutintersecting internalcavitieswillvaryinverselyastheminimumburden(rock thickness)oftherespectiveconditions.Forexample,ifthe minimumburdenforaholeinuncavitatedrockisbandthatfor cavitatedrockintheregionoftheintersectingcavityisb/2, theexpectedflyrockvelocityofthelatterisabouttwicethe former,andflyrockrangeofthelatterisaboutfourtimesthe former. Fissuresextendingclosetothefreefacemayproducean additionaldangerouseffect.Looserockswithinsuchfissures maybeshotoutas"cannon-balls";i.e.,thefissureactsasa gunbarrelandpermitsamuchlongeraccelerationtimeofthe looserockthanisnormallyenc0unteredinopenpitblasting. Incidentally,Swedishstudies 5 indicatethatlooserocks onthesurfaceofacratershotachieveaflyvelocitythatis essentiallyequivalenttothatobtainedinasimilarcratershot withoutlooserocksonitssurface. InTable9weincludedpowderfactorswheneversuch informationwasavailable.Notethatthereis no correlation betweenpowderfactorandflyrockrange.Inviewofthe discussionabovethisistobeexpected.Certainlypowder factorsprovidenoinformationaboutthepresenceofcavities orfissures.Sincepowderfactorsarecomputedfromaverage loadsperholetheyprovidelittleornowarningaboutafew holesthatmaybeoverloaded;i.e.,holesinwhichthecharge comesclosetotheboreholecollar. Incorrectorinaccuratedelaysbetweenholescanconceivably . generatewildflyrock.Thepossibleeffectsofincorrecttiming werediscussedinSection3.2.3. 47 8.0ESTIMATIONOFFLYROCKRANGEFORFIELDUSE Theresultsandconclusionsoftheprecedingsections areoflimitedvalue' unlesstheycanbeadaptedforfield use.Consequentlyaseriesofsimplechartshavebeen developedwhichgiveflyrockrangeasafunctionofshot conditions.Thesechartsaswellasdirectionfortheiruse arepresentedinAppendixD.Ifdeemedsuitable,thecontents ofAppendixDcanbedistributedtofieldpersonnel. Inthis. sectionwewillbrieflysummarizepriorattempts atestimatingflyrockrangeandpresenttherationaleforthe chartsinAppendixD. PriorAttemptsatEstimatingFlyrockRange Thereappearstobearule-of-thumbofunknownorigin andrationalewhichstatesthatflyrockrangeisthreetimes thebenchheight.'AccordingtothedatainTable10this rule-of-thumbishighlyunreliablesinceinabouttwo-thirds ofthecomparisonsshown(lowergroupinginTable10)itpredicts flyrockranges.Moreoverallbutoneofthesefalse predictionsareunderestimatesandsomearegrossunderestimates. Forbenchtopflyrockacomparisonbetweenrule-of-thumb andobservedflyrockrangeisevenworsethanthatshownin Table10forverticalfaceflyrock.Onlytwoof10comparisons arereasonablyclose.Again,therule-of-thumbgenerally grosslyunderestimatesflyrockrange. suggeststhattheratioofstemmingheightto burden(sib)bemaintainedlargerthan2/3topreventbench topflyrock.Healsosuggeststhat,ontheaverage,bidfor efficientblastingshouldbeabout30(buttherangehereis wide:14for"weak"explosivesinhardmaterialand49for "strong"explosivesinsoftmaterial).Themaximumloadper 48 BenchObserved Height::::hFlyrock3h MineRock( ft)Range(ft) MineDSandstone20'V5060 MineJPorphyry40'V100120 MinePPorphyry25