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2019 Vol.29, Issue 5 Preview Page

Original Article

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

근접병설터널에서 필라부 안전율 평가를 위한 강도감소법의 적용성 연구

Sung-Kwon Jun1
,
Dong-Ho Yoon2
,
Jae-Joon Song2*
,
Se Hyung Kim3
전 성권1
,
윤 동호2
,
송 재준2*
,
김 세형3
1Taeyoung Engineering & Construction
2Department of Energy Systems Engineering, Seoul National University
3Korea Expressway Corporation
1(주)태영건설
2서울대학교 공과대학 에너지시스템공학부
3한국도로공사
* Corresponding Author
31 October 2019. pp. 346-355
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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.

Keywords
Closely spaced tunnel
Pillar width/tunnel diameter (PW/D)
Pillar safety factor
Tension bolt
Strength reduction method(SRM)

근접병설터널에서 필라의 안정성을 평가할 때, 필라 폭이 최소가 되는 지점에서의 국부안전율(강도/응력비)을 조사하는 방법이 널리 사용된다. FEM 응력해석결과를 바탕으로 국부안전율이 1.0 이하인 경우는 필라의 안정성이 확보되지 못 하는 것으로 판단하고 인장볼트 등의 보강공법을 적용하고 있다. 그러나 국부안전율은 필라폭/터널반경(PW/D)의 변화와 무관하게 일정한 값을 보이고 있으며 인장볼트의 프리스트레싱 도입 시에도 축차응력의 변화가 크지 않아 상대적으로 필라의 안전율을 과소평가 할 수 있는 것으로 분석되었다. 아울러 Hoek and Brown(1980)이 제안한 평균안전율을 검토하였으나 상대적으로 필라폭의 크기가 커질 경우 필라의 안전율을 과대평가하는 현상을 관찰할 수 있었다. 이에 대한 대안으로 강도 감소법을 이용한 SRM 안전율을 도입하여 필라의 안정성을 평가한 결과 필라폭/터널반경 변화에 따른 무보강 및 인장볼트 보강효과가 잘 반영됨을 알 수 있었으며 파괴형상 또한 기존 극한 이론의 검토결과와 유사함을 알 수 있었다. 본 연구에서는 인장볼트의 보강효과를 구별하기 위해 록볼트 및 숏크리트를 고려하지 않고 안전율을 평가하였다.

키워드
근접병설터널
필라폭/터널반경(PW/D)
필라 안전율
인장볼트
강도감소법(SRM)
References
1
Hoek, E.I. and Brown E.T., 1980, Underground Excavation in Rock, The Institution of Mining and Metallurgy, London. 202-203.
2
Im, S.B., Lee, S.M., Lee, J.W. and Paik, Y.S., 1994, Considerable Parameters and Progressive Failure of Rock Masses due to the Tunnel Excavation, In Proceedings of KGS Fall '94 National Conference, 231-234, Seoul, Korea, Korean Geotechnical Society.
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Information
  • Publisher :Korean Society for Rock Mechanics and Rock Engineering
  • Publisher(Ko) :한국암반공학회
  • Journal Title :Tunnel and Underground Space
  • Journal Title(Ko) :터널과 지하공간
  • Volume : 29
  • No :5
  • Pages :346-355
  • Received Date : 2019-09-26
  • Revised Date : 2019-10-24
  • Accepted Date : 2019-10-28
  • DOI :https://doi.org/10.7474/TUS.2019.29.5.346
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