Section 2:Blasting action of single charge(1)crushedzoneinternal(compressionzoneaction(2)crackedzone(fracturedzone)BAtangential tensionby radial compressionRInternalaction--radialcrack2-circumferentialcrackFormation mechanismof radialrc-radiusofcharge Rc-radiusofcrushedzonecrackandcircumferential crackRp-radiusofcrackedzone2016/11/9Chapter5:Mechanicsofrockblasting
2016/11/9 Chapter 5: Mechanics of rock blasting 7 Section 2: Blasting action of single charge Internal action 1—radial crack 2—circumferential crack rc－radius of charge Rc －radius of crushed zone Rp －radius of cracked zone internal action （1）crushed zone（compression zone） （2）cracked zone（fractured zone） Formation mechanism of radial crack and circumferential crack tangential tension by radial compression
(2)external blastingactionby single charge(2)reflectivetensilestress wave makes radial crack growExternalaction0=90BreflectivetensilestresswaveradiumcrackEffectofreflectivetensilestresswaveonradial crack2016/11/9Chapter5:Mechanicsofrockblasting
2016/11/9 Chapter 5: Mechanics of rock blasting 8 （2） reflective tensile stress wave makes radial crack grow Effect of reflective tensile stress wave on radial crack External action external blasting action by single charge （2）
(3)external blastingaction by singlecharge(3)analysis of stress field(consideringinfluence of free surface)External011=actionexplosionsourceDirectionof,andOwhentensile stresstakes a maximumvalue1.821.41.6Xu501=MX十小×××Stressanalysis on pointAinrockmassDirection of principle stressO,and22016/11/9Chapter5:Mechanicsofrockblasting
external blasting action by single charge （3） 2016/11/9 Chapter 5: Mechanics of rock blasting 9 Direction of principle stress and （3）analysis of stress field (considering influence of free surface) Stress analysis on point A in rock mass Direction of and when tensile stress takes a maximum value 1 2 2 1 2 External action
Processof rockfailure when blastinghappensCBStage threeAStage twoStage oneExpansionReflectiveShock wavepressure ofmakesrockstress waveexplosiongasescompressedmakes spallmakesradialfallon radialcrackgrowdirection.102016/11/9Chapter5:Mechanicsofrockblasting
2016/11/9 Chapter 5: Mechanics of rock blasting 10 Process of rock failure when blasting happens Shock wave makes rock compressed on radial direction. A Stage one Expansion pressure of explosion gases makes radial crack grow C Stage three Reflective stress wave makes spall fall B Stage two
Patterns of rock failurewhen blasting happensRockwall of blastholeis crushedby compressioncrackedonradialdirectionFivepatternscracked on circumferential directionof rockby unloadingfailureReflective tensilewave makesspall falland radial crack grow.crackedbyexpansionstressofexplosiongases.112016/11/9Chapter5:Mechanicsofrockblasting
2016/11/9 Chapter 5: Mechanics of rock blasting 11 Patterns of rock failure when blasting happens Five patterns of rock failure 1 2 cracked on radial direction. 3 cracked on circumferential direction by unloading. 5 cracked by expansion stress of explosion gases. 4 Reflective tensile wave makes spall fall and radial crack grow. Rock wall of blasthole is crushed by compression