Geophysical And Geotechnical Investigation Of The Effect Of Blasting And Open Cast Mining On Worked-out Underground Mines And Modes Of Failure Of These Workings

摘要

To make the method of coalmining known as 'strip-mining'udeconomically viable extremely large amounts of explosive need coudbe detonated in any one particular blast. This is to ensure enoughudrock is broken co keep the large earthmoving machinery, used in thisudtype of mining, productive. This type of coal-mining operationudwas undertaken at Rieespruit Opencast Colliery in the Eastern Transvaal.udAdjacent to this colliery is an exiting underground coalmine,udand it was feared that the large amount of energy releasedudby the surface blasting would be sufficient to damage the coal pillars.udThe investigation of the above problem formed the basis of this dissertation.udMoving-coil seismometers were installed underground in what wasudconsidered^ a representative pillar, and continuous records of groundudparticle motion due to blasting were obtained from these instruments.udFurther field instrumentation consist of tape-recording decks andudelectronic packages to amplify and record the seismic signals was locatedudon surface in an instrument hut built specifically for thisudpurpose.udThe object of obtaining the above records was to establish damageudcriteria, whereby change weight could be estimated, for given distancesudfrom the blast to the underground workings, which would not cause appreciableuddamage underground. Propagation laws were established relatingudpeak particle velocity, which is widely used as an indicator ofudpossible damage, to the distance from the blast and either the square rootudor cube-root of the maximum charge weight per delay. These resultsudare presented graphically and could be used to determine allowableudcharge weights to ensure a certain particle velocity is not exceeded.