KSCE Journal of Civil and Environmental Engineering Research (대한토목학회논문집)

Korean Society of Civil Engeneers (대한토목학회)
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Evaluation on Reinforcing Effect of Inclined System Bolting by Model Tests and Numerical Analysis

모형시험 및 수치해석을 통한 경사 시스템 록볼트의 보강효과 분석

  • Received : 2013.02.14
  • Accepted : 2013.06.18
  • Published : 2013.07.30
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Abstract

Recent case studies in Japan have shown that rockbolts are commonly installed at an oblique angle to the excavation direction of the tunnel, instead of at a right angle, due to restriction of the working space. In particular, in the case of expansion in an existing tunnel, the working space can be very small, due to the large protective structures necessary to operate within an existing tunnel. In this case, where both the current use of the existing tunnel, and the reinforcement of the ground around the tunnel are required, the effects of installation angles and patterns of rockbolts are important factors in the design process. Therefore, in this study, a total number of 24 model tests are performed, to investigate the reinforcing effects of system bolting installed obliquely from the excavation direction of the tunnel, by changing the installation angle of bolts, longitudinal distance, and bonded length of bolts. The model test results indicate that the relaxed load ratio decreases, with the increase of both the bonded lengths and the number of the installed bolts, resulting in the decrease of the supported area by one bolt. Two-dimensional numerical analysis, which considered the reinforcement effect of inclined system bolting as the change of engineering properties near the tunnel, demonstrated that the deflection patterns at the tunnel crown in the numerical simulations, show a similar tendency to those measured in the model tests.

최근에 일본의 시공사례에 따르면 터널확대를 위해 보호공(프로텍터)을 설치하고 기존 터널을 사용하면서 시공하는 경우에는 록볼트를 굴착방향에 수직하게 타설할 수 없어서 경사지게 타설하는 경우가 있다. 운용 중인 터널을 확대 시공하는 경우에는 작업조건이 매우 나쁘기 때문에 록볼트의 패턴(경사 록볼트 설치, 사전 록볼트 시공, 록볼트 제외 등)에 대한 검토가 필요하다. 이 연구에서는 모형시험을 이용하여 일반적으로 터널 굴착방향과 수직하게 설치되는 시스템 록볼트의 보강효과와 터널 굴착방향에 경사지게 설치되는 경사 시스템 록볼트의 보강효과를 비교하였다. 모형 록볼트의 설치각도, 설치간격, 정착 길이 등을 변화시켜 총 24회의 모형시험을 수행하였으며, 모형시험 결과 모형볼트 1개가 부담하는 면적에 대한 이완하중 발생률은 부담면적 감소에 따라 감소하는 것으로 나타났다. 또한, 모형볼트 정착 길이 변화에 따른 이완하중 발생률은 정착 길이가 길어질수록 감소하는 경향이 나타났다. 한편 터널 지보재 설치효과를 주변 지반의 공학적 특성 증가로 간주하는 지보재 모형화 방법에 의한 2차원 수치해석 결과가 모형시험의 처짐 증가량 발생경향을 유사하게 예측하는 것으로 나타나 본 해석 기법이 경사 시스템 록볼트의 보강효과를 적절히 모사할 수 있을 것으로 판단된다.

Keywords

References

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