• Explosives and Blasting
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• v.34 no.3
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• pp.10-16
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• 2016

Recently, transition from open pit to underground mining in limestone mines is an increasing trend in Korea due to environmental issues such as noise, dust and vibrations caused by crushers and equipment. The severe damages in the surrounding rock mass of underground opening caused by explosive blasting may lead to rock fall hazards or casualties. It is well known that variables which mainly affect blast-induced rock falls in underground mining are: blast vibration level, joint orientation and distribution and shape of the cross sections of underground structures. In this study, UDEC program, which is a DEM code, is used to simulate blast vibration-induced rock fall in underground openings. Variation of joint space, joint angle and joint normal stiffness was considered to investigate the effect of joint characteristics on the blast vibration-induced rock fall in underground opening. Finally, jointed rock mass models considering blast-induced damage zone were examined to simulate the critical blast vibration value which may cause rock falls in underground opening.

• Tunnel and Underground Space
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• v.7 no.2
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• pp.116-129
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• 1997

The objective of this study is to predict the minimization effect of the noise and vibration during the construction and the train operation regarding to the design modification of the Taegu Subway Line No. 1. It was suggested optimal control blasting methods to reduce the causing vibration Nuance to the resident in City Taegu and also proposed the better governing method to decrease the environmental hazard to the near buildings and residents during the train operation. When the high-density gaseous reaction of explosion products exerts a high pressure in motion outward, a dynamic stress field will be created in the surrounding buildings. Therefore, in the region close to the charge, permanent damage begins to occur at a great critical level of partial velocity, that is difficult from different structure as working conditions. It is reliable to predict that the damages could be reduced if we know the peak velocity and the exact reasons through the conducting of detail studies of structural analysis of the related buildings with the optimal blasting designs. A blasting technique should be deemed to take advantage of the reduction of damage of the surrounding rocks and structures to improve the in-city blasting. This is a typical in-city blasting operation where success depends on closely controlling the ground vibrations in case of better designed blasting methods. There are techniques that can be applied to prevent large vibrations from damaging the important buildings through the Route Modification of the Taegu Subway Line No. 1.

• Explosives and Blasting
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• v.21 no.1
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• pp.69-76
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• 2003

Test blasting has been performed with V-cut to investigate the characteristics. Blasting vibrations were measured at two directions, the proceed direction and side direction. Propagation characteristics were determined by regression analysis; square root scaled distance and cube root scaled distance with maximum charge per delay of the blast. Testing result, The cross point was 62m in the allowable vibration velocity of 3mm/sec and 46m In 5mm/sec. Also, vibration level with measuring point was highest and decayed fastest, adapting to cube root scaled distance, for the proceed direction on ground.

• Explosives and Blasting
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• v.29 no.1
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• pp.1-9
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• 2011

Air deck charge blasting method which has been generally used in a surface mine and large scale developing site is one of the improved techniques with blasting effectiveness. Many studies and experiments have been tried to investigate the characteristics of pressure distribution in a blasting hole and increase the effectiveness of air deck charge blasting method. In this study, changes of pressure occurred in sections of air deck installed in various ways was computed and also changes of pressure with the location and length of air deck was analyzed, using numerical analysis program. Basically, all the numerical analysis was 2-Dimensional analysis and equation of status of explosives was JWL-EOS. Only to evaluate the variations of pressure in blast hole, it was assumed that rock mass is homogeneous but rock mass has different density and intensity.

• Tunnel and Underground Space
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• v.18 no.1
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• pp.33-43
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• 2008

The techniques for measuring the bulking factor of rock mass in subsidence area have never been well known all over the world. The volumetric expansion ratios obtained from blasting operation were the only way of acquiring the bulking factor of rock mass. The bulking factor of rock mass obtained from blasting operation, however, has been seldom classified in a certain criterion. Also the bulking factor of rock mass can be very dependent upon rock types. In order to overcome this limitation obtained from these reasons, the authors studied the experimental bulking factor of rock mass according to the stacking shapes as well as the overburden stresses. Gneiss, limestone and shale were chosen for testing specimens, and each bulking factor has been measured with laboratory test of applying a constant load on the fragmented rock specimens.

• Geomechanics and Engineering
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• v.23 no.6
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• pp.535-546
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• 2020

The stress environment of deep rock masses is complex. Under the action of earthquakes or blasting, the strength and stability of anchored rock masses in fracture zones or faults are affected. To explore the variation in anchored rock masses under creep-fatigue loading, shear creep comparative testing of anchored marble specimens with or without fatigue loading is performed. Considering the damage variable of rock under fatigue loading, a rheological model is established to characterize the whole shear creep process of anchored rock masses under creep-fatigue loading. The results show that (1) the overall deformation of marble under creep-fatigue loading is larger than that under only shear creep loading, and the average deformation is increased by 18.3%. (2) By comparing the creep curves with and without fatigue loading, the two curves basically coincide when the first level stress is applied, and the two curves are stable with the increase in stress level. The results show that the strain difference among the specimens increases gradually in the steady-state stage and reaches the maximum at the fourth level. (3) The shear creep is described by considering the creep mechanical properties of anchored rock masses under fatigue loading. The accuracy of this creep-fatigue model is verified by laboratory tests, and the applicability of the model is illustrated by the fitting parameter R2. The proposed model provides a theoretical basis for the study of anchored rock masses under low-frequency earthquakes or blasting and new methods for the stability and reinforcement of rock masses.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.167-178
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• 2003

Damage and overbreak of the remaining rock induced by blasting can not be avoided during tunnel construction which may result in either short-term or long-term tunnel instability. Therefore, in this paper, a methodology to take into account the effect of blast-induced damage in tunnel stability assessment is proposed. Dynamic numerical analysis was executed to evaluate damage and overbreak of the remaining rock for the most common blasting pattern in road tunnel. Rock damage was quantified by utilizing the damage variable factor which is adopted proposed in continuum damage mechanics. The damaged rock stiffness and the damaged failure criteria are used to consider the effect of rock damage in tunnel stability analysis. The damaged geological strength index of the damaged rock was newly proposed from the relationship between deformation modulus and geological strength index. Also the Hoek-Brown failure criteria of the damaged rock was obtained using the damaged geological strength index. Analysing the tunnel stability with the consideration of the blast-induced damage of remaining rock, it was found that the extend of plastic zone and deformation increased compared to the undamaged rock. Therefore the short-term or long-term tunnel stability will be threatened when the rock damage from blasting is ignored in the tunnel stability analysis.

• Tunnel and Underground Space
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• v.26 no.2
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• pp.120-130
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• 2016

Considering the applicability of Kuz-Ram model, which has been used extensively for predicting rock fragmentation size distribution by blasting, to domestic open-pit limestone mine, a total of 21 blasting tests have been executed at an open-pit limestone mine in eastern Gangwon of South Korea. A comparative analysis of field measured value and Kuz-Ram predicted value showed that there are a considerable amount of error in the predicted values regardless of application of various correction parameters for rock factor and uniformity factor; up to 56.45% in mean fragmentation size and 37.52% in uniformity index. Also the problem of applying different correction parameters has been derived even though a similar blasting pattern has been adopted for a same blasting bench. The authors therefore suggest that Kuz-Ram model needs to be modified for a proper application to domestic open-pit limestone mine.

• Explosives and Blasting
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• v.32 no.3
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• pp.1-9
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• 2014

Since the rock fragmentation from a bench blasting can affect the subsequent processes including loading, hauling and crushing, its control is essential for the assessment of blasting efficiency as well as production cost. In this study, the delay time could be precisely controlled by using electronic detonators. The rock fragmentations resulted from the blastings with different delay times of 1, 2, 3, 4, 5, 7 and 10ms per each meter of burden were measured from full scale field tests in a limestone mine. The results showed that the optimum delay time for minimum fragmentation was approximately 6ms/m. From the analysis of fragmentation size distribution, it was possible to find that delay time can be a parameter on rock fragmentation and thus it would be possible to control rock fragmentation by adjusting delay time.

• Tunnel and Underground Space
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• v.33 no.6
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• pp.472-482
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• 2023

The grid-type or room-and-pillar method is applied for the purpose of mining horizontally buried minerals. In this study, design and pilot test were performed to apply the room-and-pillar method which uses natural rock as a rock pillar to the construction of underground space. The area where the pilot test was conducted was in stone mine and had good rock conditions with an appropriate depth (about 30 m) to apply the pilot test. The pilot test site was selected by reviewing accessibility and ground conditions and then site construction was performed through detailed ground investigation and design. The pilot test was designed with a column shape of 8×8 m and a cross-section of 8×12 m. The blasting pattern was determined through test blasting at the site, and blasting of 3 m excavation with 89 holes was performed. Through field observations, the average width of 12.5 m and the average height of 8.3 m were measured. Therefore, it is possible to proceed similar to the cross-sectional shape considered in the design.