• Explosives and Blasting
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• v.31 no.1
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• pp.49-54
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• 2013

External charges with four different kinds of tamping materials are tested to determine the effect of tamping on the blasting of steel components and concrete blocks. The tamping materials used are tamping cap, urethane foam, sand bag and mud. As a result, the tamping cap, urethane foam, and sand bag show no significant effect of tamping. But the mud tamping shows that the charge amount can be reduced by more than 20% in completely cutting the structural components. In addition, it is found from the test that the standard equation for calculating the proper charge is rather conservative, which means the equation overestimates the necessary charge for the blasting.

• Explosives and Blasting
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• v.36 no.3
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• pp.19-28
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• 2018

Locally damaged structures caused by earthquake or extraordinary external forces have been required to rapidly be dismantled because of its possibility of additional collapses. Particularly, steel frame structures were demolished by the shaped charge blasting method. Recently a research suggested a shape charge blasting technique which uses bent-shaped charge holder of copper plate and emulsion explosive charge to cut thick steel plates. This study simulated the cutting performance of the bent-shaped charge holder with considering types of explosives, thickness of copper liner and stand-off distances using LS-DYNA software. The shape charge blasting test of a 25mm thickness steel plate were used to calibrate the input parameters of the numerical models. The penetration depth and penetration width were analysed with different types of explosives, thickness of copper liner and stand-off distances.

• Explosives and Blasting
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• v.34 no.4
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• pp.1-9
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• 2016

For underwater steel structure, cut that underwater shaped charge device that combines a spring hose, which is an external device of pressure resistance and flexibility with flexible shaped charge, was invented. As a basic experiment for an optimum condition design, an penetration performance was compared by external device shape. To evaluate the result of an experiment, image analysis was carried out after obtaining the model by using the liquid rubber for the penetrated steel plate. To simulate the penetrating process of shaped charge, the AUTODYN program has been used. As a result of analysis, while the average penetration depth of circular and square shaped external devices were similar, the penetration quality was more uniform in the case of circle. In addition, water infiltration occurred in square case, displacement and strain rate according to the increase of the water pressure were measured high.

• Explosives and Blasting
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• v.32 no.1
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• pp.1-9
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• 2014

TNT was blasted on the surface of steel plates and concrete block to study the effect of separation distance between object and charge. The equation of US Army Corps of Engineers turned out to be rather conservative. Effect of separation distance is larger for steel plate than concrete block. Steel plate cannot be cut by standard or more charge in the case of 2 cm separation while the concrete block can be crushed with the same distance.

• Explosives and Blasting
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• v.13 no.1
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• pp.20-31
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• 1995

Many methods and techniques to reduce ground vibrations are well known. Some of them are to adopt electric milisecond detonators with a sequential blasting machine or an initiating system with an adequate number of delay intervals. The types of electric detonators munufactured in Korea include instantaneous, decisecond and milisecond delays byt numbers of delay intervals are only limite from No.1 to No.20 respectively. It is not sufficient to control accurately milisecond time with these detonators in tunnel excavation. Sequential fire time refers to adding an external time delay to a detonators norminal firing time to obtain sequential initiation and it is determined by sequential timer setting. To reduce the vibration level, sequential blasting machine with decisecond detonatore was adopted. A total of 134 blasting was recorded at various sites. Blast-to-structure distances ranged from 20.3 to 42.0 meter, where charge weight varied from 0.25 to 0.75 kg per delay. The results can be summarized as follow : 1. The effects of sequential blasting machine on the vibration level are discussed. The vibration level by S.B.M. are decreased approximately 14.38~18.05 to compare to level of conventional blasting and cycle time per round can be saved. 2. The empirical equations of particle velocity were obtained in S,B.M. and conventional blastin. $V=K(D/W^{1/3})-n$. where the values for n and k are estimated to be 1.665 to 1.710 and 93.59 to 137 respectively. 3. The growth of cracks due to vibrations are found but the level fall to within allowable value.

• Explosives and Blasting
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• v.36 no.3
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• pp.29-38
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• 2018

With the recent industrial developments and economic development nationally, there has been a rapidly increasing demand for the use of underground space as locations for establishing social infrastructure and various convenience facilities. In this study, a mist-control system was developed to reduce the generation of dust in underground blasting. To enhance the dust-reduction effect, a guiding device was developed which is capable of adjusting the direction of the spray toward's the blasting face of mine or tunnel. A numerical analysis was performed by using the AUTODYN software, and results were compared with those published in basic experiments. To verify the mist-diffusion effect according to the position of explosives in a water bag, numerical analyses were conducted for the following cases: Explosives were set in the middle, and in the bottom of the water bag. The optimum condition was external detonation and center charge. The mist particle size from the result was suitable for the reduction of dust after blasting in underground mine and tunnel.

• Tunnel and Underground Space
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• v.4 no.2
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• pp.132-143
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• 1994

Many methods and techniques to reduce ground vibrations are well known. Some of them are to adopt electric millisecond detonators with a sequential blasting machine or an initiating system with an adequate number of delay intervals. The types of electric detonators manufactured in korea include instantaneous, decisecond and millisecond delays but numbers of delay intervals are only limited from No.1 to No.20 respectively. It is not sufficient to control accurately millisecond time with these detonators in tunnel excavation. Sequential fire time refers to adding an external time delay to a detonators norminal firing time to obtain sequential initiation and it is determined by sequential timer setting. To reduce the vibration level, sequential blasting machine(S.B.M) with decisecond detonators was adopted. A total of 134 blasts was recorede at various sites. Blast-to-structure distances ranged from 20.3 to 42.0 meter, where charge weight varied from 0.24 to 0.75 kg per delay. The results can be summarized as follow: 1. The effects of sequential blasting machine on the vibration level are discussed. The vibration level by S.B.M are decreased approximately 14.38~18.05% compare to level of conventional blasting and cycle time per round can be saved. 2. The empirical equations of particle velocity were obtained in S.B.M and conventional blasting. V=K(D/W1/3)-n, where the values for n and k are estimated to be 1.665 to 1.710 and 93.59 to 137 respectively. 3. The growth of cracks due to vibrations are found but the level fall to within allowable value.

• Tunnel and Underground Space
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• v.25 no.1
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• pp.46-55
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• 2015

A water tube with detonating cord was devised to control the blast dust. Water diffusion experiments with different detonating cord positions were conducted during the series of experiments to optimize the design parameters of the tube. Images from high speed camera were analyzed to evaluate the results. AUTODYN program was adopted to simulate the diffusion process of water and compared with the images. Diffusion of water shows cross flow in case of external charge while the internal case shows radial flow. A bubble ring was formed during the numerical analysis of internal charge case as occurred in underwater blast. An additional bubble ring was formed by the reflection pressure from the ground. And the Weber number was determined as sufficient for spray atomization performance of the water tube.