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Application of Strength Reduction Method to Evaluation of Pillar Safety Factor in very Closely Spaced Tunnels

근접병설터널에서 필라부 안전율 평가를 위한 강도감소법의 적용성 연구

  • Jun, Sung-Kwon (Taeyoung Engineering & Construction) ;
  • Yoon, Dong-Ho (Department of Energy Systems Engineering, Seoul National University) ;
  • Song, Jae-Joon (Department of Energy Systems Engineering, Seoul National University) ;
  • Kim, Se Hyung (Korea Expressway Corporation)
  • 전성권 ((주)태영건설) ;
  • 윤동호 (서울대학교 공과대학 에너지시스템공학부) ;
  • 송재준 (서울대학교 공과대학 에너지시스템공학부) ;
  • 김세형 (한국도로공사)
  • Received : 2019.06.26
  • Accepted : 2019.10.28
  • Published : 2019.10.31

Abstract

When evaluating pillar stability in very closely spaced tunnels, a local safety factor (strength/stress ratio) at the minimum width has been widely used. Tension bolts have been frequently applied as reinforcement for the cases where safety factors are less than 1.0 from FEM stress analysis. However, the local safety factor shows a constant value irrespective of the change in pillar width/tunnel diameter (PW/D) and the safety factor of the pillar is underestimated because the variation of deviation stress is relatively small even when the pre-stressing is applied to the tension bolt. In addition, the average safety factor proposed by Hoek and Brown(1980) was reviewed, but the pillar safety factor was relatively overestimated when the width of the pillar was increased. As an alternative, the SRM safety factor using shear strength reduction method shows the effect of changing the safety factor in the case of no reinforcement and tension bolt reinforcement as the pillar width/tunnel diameter(PW/D) changes. The failure shape is also similar to the previous limit theory result. In this study, the safety factor was evaluated without considering rock bolt and shotcrete to distinguish reinforcing effect of tension bolt.

Acknowledgement

Supported by : 한국에너지기술평가원(KETEP)

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