• Title/Summary/Keyword: rock blasting

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A Evaluation of Standard Support Pattern for Two-Arch Road Tunnel (2-Arch 도로터널에 적용된 표준지보패턴의 적정성 검토)

  • Chun, Byungsik;Choi, Kwangbo;Kim, Hyeyang;Yoo, Junhee
    • Journal of the Korean GEO-environmental Society
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    • v.9 no.7
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    • pp.25-35
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    • 2008
  • In domestic cases, the standard support pattern of 2-lanes road tunnels is presented because construction experience and high degree various data was abundant. But, it is not desirable to apply standard for 2-Arch tunnels that the precedent and measuring data is insufficient existing support pattern blasting plan and interpretation of separate way concerning specific terrain and rock quality. In this study, behavior according to load distribution ratio and Unsymmetrical Pressure about standard support pattern which is applied in design and construction of 2-arch tunnels was analysed and the examination of blasting vibration has influence on the center wall is conducted as a consequence reasonableness of support whether or not with presumed support pressure and ground reaction curve method. In result appropriateness of standard support pattern, support quantity is proper but considers specific terrain and rock quality condition when design and construction of further step 2-arch tunnel standard support pattern must be decided by considering terrains, soil properties and construction condition of the objective tunnel.

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Experiment and Evaluation of Mist Diffusion from Water Tube for Blasting Dust Control in accordance with the Explosives Position (폭약 기폭위치에 따른 발파 분진제어용 워터튜브 주입수의 분무확산 실험 및 평가)

  • Yang, Hyung-Sik;Ko, Young-Hun;Kim, Jung-Gyu;Noh, You-Song;Park, Hoon;Cho, Sang-Ho
    • 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.

A Study on the Improvement of a Charging and Initiating Method in a Tunnel Excavation (터널굴진에서 장약 및 기폭방법 개선에 관한 연구)

  • Oh, E-Hwan;Won, Yeon-Ho;Lim, Han-Uk
    • Explosives and Blasting
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    • v.24 no.2
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    • pp.1-8
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    • 2006
  • In this study, a charging density has been differently applied to all holes to improve an excavated length per round on excavating a tunnel in quartzite mine and to prevent a dead pressure phenomena and sintering phenomena. A composition initiating system using simultaneously a direct initiating system and a indirect initiating system with 2 detonators in one hole has been introduced to cut holes. As a bottom part which is difficult to make a free face are charged with a higher charging density and a column part are charged with a lower charging density, the composition charging and initiating system which the power of explosives works effectively in the rock mass is developed. As the results, a dead pressure phenomena and a sintering phenomena being often produced in a hard rock or in a long hole could be prevented. Besides, the workability was improved by about 15% and the specific charge was reduced to about 20%, as an excavated length vs. a drilled length per round could be increased over 95%.

A Comparative Study on the Tensile Strength of Frozen Soil according to Test Methods (시험 방법에 따른 동결토의 인장강도)

  • Seo, Young-Kyo;Kang, Hyo-Sub
    • Journal of the Korean Geotechnical Society
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    • v.24 no.4
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    • pp.57-66
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    • 2008
  • In this study, the blast-induced vibration effects on the structural stability of the adjacent tunnel and the stability were estimated with respect to the allowable peak particle velocity (PPV). The blasting distance from the tunnel satisfying the allowable PPV was estimated based on the analytical solutions, United States Bureau of Mines (USBM) suggestions, and the equations used in the subway in Seoul. The allowable blasting distance was estimated by using finite difference analysis (FDA) and the behavior of the concrete lining and rock bolts was examined and the stability of those was estimated during the blast. Research results show that the blast-induced vibration effects on the structural stability are negligible for the concrete lining but relatively large for the rock bolts.

An Experimental Study on the Determination of Damage Thresholds in Rock at Different Stress Levels (응력수준에 따른 암석의 손상기준 결정에 관한 실험적 연구)

  • Chang Soo-Ho;Lee Chung-In
    • Explosives and Blasting
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    • v.23 no.4
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    • pp.31-44
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    • 2005
  • In highly stressed conditions, the excavation damage zone induced by stress redistribution and disturbance must be evaluated after tunnel excavation. Therefore, the investigation of stress-induced deformation and fracture in rock is indispensable. In this study, fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by the moving point regression technique as well as acoustic emission measured during uniaxial compression tests. Especially, the modified procedures to determine damage thresholds more systematically were newly proposed, and successfully applied to rock. From experiments, crack initiation and track damage stress levels were estimated to be $33{\~}36\%$ and $84{\~}89\%$ of uniaxial compressive strength respectively, for both of Hwangdeung granite and Yeosan marble. However, the normalized crack closure stress level for Yeosan marble was much higher than for Hwangdeung granite. In addition, the largest proportion of total axial strain in Hwangdeung granite was attributable to elastic deformation and initial microcracking. However, the greatest part of axial deformation in Yeosan marble arose from initial crack closure and unstable cracking. Finally, it was seen that unstable cracking after the crack damage stress level played a key part in the lateral deformation in rocks under uniaxial compression.

Theory and Practice in the Tensile Strength Test for Split Ring Shaped Rock Specimen (터진고리 형태의 암석시편에 대한 인장강도 시험의 이론과 실제)

  • Choi, Byung-Hee;Lee, Youn-Kyou;Park, Chan;Park, Chulwhan
    • Explosives and Blasting
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    • v.38 no.1
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    • pp.30-37
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    • 2020
  • In this study the split ring (SR) test was investigated for its applicability to the measurement of the tensile strength of rock specimen of NX size. The concept of the SR test is the same as the half ring (HR) test (Choi et al., 2019) except that the expected fracture plane is perpendicular to the loading direction. Because of this perpendicularity, however, it was believed that the SR test could be more accurate than the HR test. Like the HR specimen, the SR specimen is a curved prismatic bar with a uniform section. Appealing to a basic bending theory in strength of materials, the tensile strength for the special bar can be calculated analytically. Numerical simulations using LS-DYNA revealed, as expected, that the strength errors were 1% and 5% for the tensional and compressional SR tests, respectively, which were much lower than that (12%) of the HR test. To identify the performance of the two SR tests, laboratory experiments were conducted. The HR and Brazilian tests were also performed for comparison. The experiments showed that the ratios of the tensional and compressional SR to Brazilian strengths were 1.2~1.4 and 1.1~1.2, respectively, which are too small compared to empirical values in ordinary bend tests. Consequently, it is concluded that the SR test is not appropriate for use in tensile strength test of rock specimen of NX size. But the ratio of the HR to Brazilian strengths was within 1.7~2.0 for both the previous and present studies, showing a good consistency in their test results.

An Experimental Study on Crack Growth in Rock-like Material under Monotinic and Cyclic Loading (단조증가 및 반복하중 하에서 모사 암석 시료의 균열 성장에 관한 실험적 연구)

  • Ko, Tae-Young;Lee, Seung-Cheol;Kim, Dong-Keun;Choi, Young-Tae
    • Tunnel and Underground Space
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    • v.21 no.4
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    • pp.307-319
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    • 2011
  • Cyclic loading due to traffic, excavation and blasting causes microcrack growth in rocks over long period of time, and this type of loading often causes rock to fail at a lower stress than its monotonically determined strength. Thus, the crack growth and coalescence under cyclic loading are important for the long-term stability problems. In this research, experiments using gypsum as a model material for rock are carried out to investigate crack propagation and coalescence under monotonic and cyclic loading. Both monotonic and cyclic tests have a similar wing crack initiation position, wing crack initiation angle, cracking sequence and coalescence type. Three types of crack coalescence were observed; Type I, II and III. Type I coalescence occurs due to a shear crack and Type II coalescence occurs through one wing or tension crack. For Type III, coalescence occurs through two wing or tension cracks. Fatigue cracks appear in cyclic tests. Two types of fatigue crack initiation directions, coplanar and horizontal directions, are observed.

Stability Assessment of Abandoned Gangway for Commercial Utilization of Services (서비스업 활용을 위한 광산 폐갱도의 안정성 평가)

  • SunWoo, Choon;Chung, So-Keul;Lee, Yun-Su;Kang, Sang-Soo;Kang, Jung-Seok
    • Tunnel and Underground Space
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    • v.22 no.5
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    • pp.297-309
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    • 2012
  • The stability assessment of abandoned gangway for the purpose of services was performed. Among the many factors that affect the stability of openings, the span of the opening in a given rock mass condition provides an important element of design. In this paper, the stability of gangway was assessed by the critical span curves proposed by Lang, the modified Mathews'stability graph method and using support measures of the Q system. In the evaluation of stability as a whole the gangway is considered as stable. But the rockfalls of wedge-shaped blocks were expected in the area in which the horizontal joints of low angle appear. The support measures such as local rock bolts are required to use for commercial purposes of the abandoned gangway. And entrance section may require the particular attention as unstable section. Since there are so many spalling due to bad blasting in the roof and sidewall of gangway, the scaling operations should be followed primarily.

A Study on Effect of Shotcrete Adhesive Strength on Large Section Rock Tunnel Stability (대단면 암반터널의 안정성에 미치는 숏크리트 부착강도의 영향에 관한 연구)

  • Chang, Seok-Bue;Hong, Eui-Joon;Moon, Sang-Jo
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.7 no.4
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    • pp.305-311
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    • 2005
  • Shotcrete adhesive strength in large section tunnels in jointed rock masses plays an important role in preventing rock block from falling and shotcrete debonding due to blasting vibration. Nevertheless, it has not been considered as a major factor such as shotcrete compressive strength in design and construction. For this reason, the purpose of this study is to analyze the effect on shotcrete adhesive strength for large-sectioned tunnels. First, the parametric study using numerical model similar to Holmgren's punch-loaded test was executed for various range of adhesive strength. It shows that the shotcrete bearing capacity is linearly proportioned to the adhesive strength between shotcrete layer and blocks. And then, distinct element analysis of a jointed rock tunnel for an adhesive strength of 1 MPa and a conventional fully-bonded condition between the shotcrete layer and the excavation face was compared in order to evaluate the effect of the shotcrete adhesive strength.

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Assessment of Blast-induced Vibration Using Dynamic Distinct Element Analysis (불연속체 동해석 기법을 이용한 발파진동 영향평가)

  • Park, Byung-Ki;Jeon, Seokwon;Park, Gwang-Jun;Do, Deog-Soo;Kim, Tae-Hoon;Jung, Du-Seop
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.12 s.105
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    • pp.1389-1397
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    • 2005
  • Since blast-induced vibration may cause serious problem to the rock mass as well as the nearby structures, the prediction of blast-induced nitration and the stability evaluation must be performed before blasting activities. Dynamic analysis has been increased recently in order to analyze the effect of the blast-Induced vibration. Most of the previous studies, however, were based on the continuum analysis unable to consider rock joints which significantly affect the wave propagation and attenuation characteristics. They also adopted pressure corves estimated tv theoretical or empirical equations as input detonation load, thus there were very difficult to reflect the characteristics of propagating media. In this study, therefore, we suggested a dynamic distinct element analysis technique which uses velocity waveform obtained from a test blast as an input detonation load. A distinct element program, UDEC was used to consider the effect of rock joints. In order to verify the validity of proposed method, the test blast was simulated. The predicted results from the proposed method showed a good agreement with the measured vibration data from the test blast. Through the dynamic numerical modelling on the planned road tunnel and slope, we evaluated the effect of blast-induced nitration and the stability of rock slope.