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1 <br /> o To improve the safety of shove! ooeratioaz beneath critical faros, progressive excavation barl <br />t to final configuration is recommended Stage 3 of as exavatioa sequence illustrated is Figure <br /> 35 iactudes the provision of a temporary toe buttress The purpose of such a bu[trcss is az <br /> follows: <br />' - To allow time and partial relief of the toe of a failure to occur so that the failure can <br /> be identified by monitoring and remedial action taken <br />' - To afford maximum proteaiaa to the equipment working oa the beach. <br /> - To afford maumum space for the exctvation equipment ro operate. <br />' i <br /> - To aid <br />s egttipmem retrieval by assuring adequate operating space around a failure, <br /> should it occur. <br />' There are two generally accepted methods of reduang blast damage: <br /> o Redttaioa of Marge weight per delay. <br />1 ll <br />l <br />i <br />B <br />ff <br />h <br /> o Final wa <br />ng - ( <br />u <br />er pre s <br />ear, etc) <br />b <br />ast <br />' az illustrated in Figure L _ <br /> Reduction is damage by reduuioa is the charge weight per delay is covered by the relaiotship of the <br /> peak particle veloary (a measure of the blasting vibrations) to the amount of explosive anal the distance <br />' from the detonation The following threshold values have beta suggested: <br /> Particle Velodry Damage <br />' Ta/Sec <br /> 2 Limit of damage to buildings (less than 5%) <br /> 5 Minor damage ro buildings <br />L Rockfalls in unlined tunnels <br /> S Onset of Qackiag of rock <br /> 100 Breakage of rock <br />1 i <br />k <br />h <br />l <br />d di <br />b <br />h <br />f <br />ll <br />i <br />l <br />l <br />a <br />l <br />d <br />h <br />k <br />i <br />b <br /> ow <br />to w <br />nown az t <br />e so <br />e <br />stance <br />y t <br />e <br />o <br />ng <br />e ve <br />ry can <br />e re <br />ate <br />at <br />s <br />The pea <br />part <br />c <br />o <br /> Particle veladry = K TSTANCE FROM BLAS <br />' EXPLOSIVE ~V[' <br /> whue k and B are constants which are site and blasting method specfie Fgure 3 shows the <br />' relationship for a general site. This plot should only be toed for very general guidance. The derivation <br /> of this type of relationship nn be gained by simple moniroriag, with a vioratioa recorder and geophoae <br /> of aial or production blasts. <br />' <br /> Fgure 3 shows that production blasts of 100 m. per delay should be detonated ao closer thaw <br /> appro~cmately 33 feet from the final wall. Final wall blasts containing charge weights of SO llb. of <br /> <br />' ANFO should be detonated ao closer than 25 feet from the final wa1L <br /> Therefore the first seep is reduang blasting damage is very simply [o reduce the charge weight per <br /> delayiatervaL <br />1 <br />1 <br /> <br />