《爆破工程 Blasting Engineering》课程教学课件（讲稿）Chapter 5 Mechanics of rock blasting

Chapter 5: Mechanics of rock blastingContents5.1Fundamental theoryofrockfailure5.2Blastingaction ofsingle charge5.3Blastingactionofextendedcharge5.4 Characters of rockfailure when detonatingmulti-charges5.5Principleof energy balanceand charging calculation5.6Maininfluencingfactorsonblastingeffect2016/11/9Chapter5:Mechanicsof rockblasting

2016/11/9 Chapter 5: Mechanics of rock blasting 2 Contents Chapter 5: Mechanics of rock blasting 5.1 Fundamental theory of rock failure 5.2 Blasting action of single charge 5.3 Blasting action of extended charge 5.4 Characters of rock failure when detonating multi-charges 5.5 Principle of energy balance and charging calculation 5.6 Main influencing factors on blasting effect ：

Section 1:Fundamental theory of rock failure （1)ExpansiveactionofexpansiongasesHTensile action ofreflectivestresswaveComprehensiveactionwithExpansionof explosiongasesexpansionandtension2016/11/9Chapter5:Mechanicsofrockblasting

2016/11/9 Chapter 5: Mechanics of rock blasting 3 Expansion of explosion gases Expansive action of expansion gases Tensile action of reflective stress wave Comprehensive action with expansion and tension Section 1: Fundamental theory of rock failure（1）

Section 1:Fundamental theory of rock failure （2)ExpansiveactionofexpansiongasesTensileactionofreflective stresswave(a)(b)Tensileactionofstress wave reflectionComprehensiveactionwitWavefrontofincidentpressurewavea)expansion andtensionWavefrontofreflectivetensilestresswave(b)R2016/11/9Chapter5:Mechanicsofrockblasting

2016/11/9 Chapter 5: Mechanics of rock blasting 4 Tensile action of stress wave reflection Expansive action of expansion gases Tensile action of reflective stress wave Comprehensive action with expansion and tension (a) Wavefront of incident pressure wave (b) Wavefront of reflective tensile stress wave Section 1: Fundamental theory of rock failure（2）

Experiments for testing tensile actionofreflectivestresswave一blastingexperimentblastingexperimentofplatedetonation experiment of1blastholeof rock bars2-crushedzonecementplate3--tensilezone 4vibrativezonewavefrontofairshockwave2--wavefront ofshockwaveincementplate-cementplate2016/11/9Chapter5:Mechanicsofrockblasting

2016/11/9 Chapter 5: Mechanics of rock blasting 5 Experiments for testing tensile action of reflective stress wave detonation experiment of cement plate 1—wavefront of air shock wave 2—wavefront of shock wave in cement plate 3—cement plate blasting experiment of rock bars blasting experiment of plate 1—blasthole 2—crushed zone 3—tensile zone 4—vibrative zone

Section1:Fundamental theoryofrockfailure （3)Expansiveaction ofEssenceofcomprehensiveaction:expansiongasesTheinitial crackisproducedbyshock wave and stress waveandfilledwithexplosiongaseswhichforcethecracktogrowfurther with quasi-static pressure.Quasi-static energy,produced by explosion gases,is the mainforce of rockfailure.Tensile action ofByA.H.XaHykaeB,three classificationsof rock:reflectivestresswave(1)Rockofhighimpedance(MPa·s/m),from15to25,isfailedmainbyincidentandreflectivestresswave(2) Rock of medium impedance, from 5 to 15, is failed mainlybycomprehensiveactionofincidentstresswaveandexplosiongases.Comprehensiveaction withexpansionandtension(3) Rock of low impedance, lower than 5, is failed mainly byexpansiveaction ofexplosiongases62016/11/9Chapter5:Mechanicsofrockblasting

2016/11/9 Chapter 5: Mechanics of rock blasting 6 Expansive action of expansion gases Tensile action of reflective stress wave Comprehensive action with expansion and tension Essence of comprehensive action： By A.H.XaHyKaeB , three classifications of rock : (1) Rock of high impedance(MPa·s/m), from 15 to 25, is failed main by incident and reflective stress wave. (2) Rock of medium impedance, from 5 to 15, is failed mainly by comprehensive action of incident stress wave and explosion gases. (3) Rock of low impedance, lower than 5, is failed mainly by expansive action of explosion gases. The initial crack is produced by shock wave and stress wave and filled with explosion gases which force the crack to grow further with quasi-static pressure. Quasi-static energy, produced by explosion gases, is the main force of rock failure. Section 1: Fundamental theory of rock failure（3）

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