Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Estimation of Attenuation Relationship Compatible with Damping Ratio of Rock Mass from Numerical Simulation

수치해석을 통한 진동감쇠식 맞춤형 암반의 감쇠비 산정

  • Kim, Nag Young (Expressway & Transportation Research Institute, Korea Expressway Corp) ;
  • Ryu, Jae-Ha (Expressway Design Evaluation Division Design Evaluation Team, Korea Expressway Corp) ;
  • Ahn, Jae-Kwang (Dept. of Civil and Env. Engr., Hanyang Univ.) ;
  • Park, Duhee (Dept. of Civil and Env. Engr., Hanyang Univ.) ;
  • Son, Murak (Dept. of Civil Engr, Daegu Univ.) ;
  • Hwang, Young-Cheol (Dept. of Civil and Engr., Sangji Univ.)
  • 김낙영 (한국도로공사 기술심사처) ;
  • 류재하 (한국도로공사 도로교통연구원 기술심의팀) ;
  • 안재광 (한양대학교 건설환경공학과) ;
  • 박두희 (한양대학교 건설환경공학과) ;
  • 손무락 (대구대학교 토목공학과) ;
  • 황영철 (상지대학교 건설시스템공학과)
  • Received : 2015.03.11
  • Accepted : 2015.04.13
  • Published : 2015.04.30
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Abstract

The stability of the adjcent structures or slopes under blasting is typically evaluated using an empirical vibration attenuation curve or dynamic numerical analysis. To perform a dynamic analysis, it is necessary to determine the blast load and the damping ratio of rock mass. Various empirical methods have been proposed for the blast load. However, a study on representative values of damping ratio of a rock mass has not yet been performed. Therefore, the damping ratio was either ignored or selected without a clear basis in performing a blast analysis. Selection of the dampring ratio for the rock mass is very difficult because the vibration propagation is influenced by the layout and properties of the rock joints. Besides, the vibration induced by blasting is propagated spherically, whereas plane waves are generated by an earthquake. Since the geometrical spreading causes additional attenuation, the damping ratio should be adjusted in the case of a 2D plane strain analysis. In this study, we proposed equivalent damping ratios for use in continuum 2D plane strain analyses. To this end, we performed 2D dynamic analyses for a wide range of rock stiffness and investigated the characteristics of blast vibration propagation. Based on numerical simulations, a correlation between the attenuation equation, shear wave velocity, and equivalent damping ratio of rock mass is presented. This novel approach is the first attempt to select the damping ratio from an attenuation relationship. The proposed chart is easy to be used and can be applied in practice.

발파에 대한 주변 구조물이나 사면의 안정성은 경험적 진동감쇠식 또는 발파진동 동적 수치해석을 통하여 평가한다. 동적해석을 수행하기 위해서는 발파하중과 지반 감쇠비의 산정이 필요하다. 발파하중에 대해서는 다양한 경험적 방법이 제시되었지만 암반의 감쇠비에 대한 연구는 제한적이며 해석 시 이를 무시하거나 명확한 근거 없이 가정하여 해석에 적용하고 있다. 암반의 감쇠비는 절리의 영향을 크게 받으므로 이를 고려해서 산정해야 한다. 또한, 평면파로 가정할 수 있는 지진파와는 다르게 발파 시에는 구면파가 생성되며 이를 2차원 해석에서 모사하는 경우에는 이의 기하학적 확산을 고려하기 위하여 감쇠비를 조정해야 한다. 본 연구에서는 위의 두 가지 영향이 고려된 2차원 평면변형률 연속체 해석에 적용 가능한 암반의 등가감쇠비를 제안하였다. 이를 위하여 다양한 강성의 암반에 대한 2차원 동적해석을 수행하여 암반의 감쇠비에 따른 진동전파 특성을 분석하였으며 해석결과를 기반으로 진동감쇠식-전단파속도-등가감쇠비와의 상관관계를 규명하였다. 제시된 상관관계는 경험적 진동감쇠식에 상응하는 감쇠비를 산정한 최초의 시도로 중요한 의미가 있으며 동시에 실무에도 쉽게 적용될 수 있는 유용한 방법이다.

Keywords

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