Study on Damage Charicteristics and Safty Threshold of Rock Vibration by Blast

Abstract: In construction site of rock blasting and foundation excavation at Ling’ao Nuclear Power Station (LNPS), Guangdong, China, rock blast vibration has been monitored. And four groups of sound wave tests before and after rock blasting have been conducted. Based on properties of rock mass and parameters of explosive, the explosion dynamic loads, the characteristics of rock damage and attenuation of peak paritcal velocity (PPV) have all been simulated by computers. Damage zone size and PPV attenuation law of rock under blasting have been acheived. According to their relation, the allowable maximum vibration velocity (which is called safty threshold) of rock partical in certain distance from charge center has been determined when damage zone size is limited to a certain value.Based on properties of rock mass and parameters of explosive, the author simulated the mechanism of crack generating and developing according to Von Mises failure criterion of geological material. It is concluded that the radius of crushing zone of rock after being blasted is approximately 3 times of that of charge column. And the radius of fracture zone is about 70 times of that of charge column. Also, the attenuation characteristics of pressure and velocity of rock particals in near region of charge holes have been studied and compared with results from corresponding theoretical calculation. Then, the variation of explosion load with charge weight is obtained and analysed.The vibration velocity of rock under blasting was monitored in construction site. Based on properties of rock material and joints, the author simulated the rock vibration velocity with distinct element method and obtained the attenuation characteristics of PPV. The results of numerical simulation are consistent with those of monitoring. By changing charge weight in numerical model, variation of rock vibration velocity with charge weight is known. It is found that the PPV in near zone of detonation decreases dramatically, and then much slower down in the far field. Besides, in area out of the near zone of detonation of rock mass, the PPV in vertical direction is greater than that in radius direction. And the PPV in both directions increase with charge weight.At the same time, researchers have conducted four groups of sound wave tests in site before and after each blasting. The change rate of sound wave travel speed through rock mass can thus be obtained. According to relation of this change rate and damage variable, the damage zone size induced by each blast is known. On the other hand, in numeriical simulation, damage zone siz…
Key words: safty threshold; blast vibration; damage; rock mass; nuclear power station; 3DEC; FLAC; DYNA

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