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Crack Coalescence in Rock Bridges under Uniaxial Compression

단축압축 하의 암석 브릿지에서의 균열결합
Nam-Su Park1
,
Seokwon Jeon2
박 남수1
,
전 석원2
1서울대학교 지구환경시스템공학부
2서울대학교 지구환경시스템공학부 조교수

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ABSTRACT

Rock masses are usually discontinuous in nature, as a result of various geological processes they have underdone and they contain rock joints and bridges. Crack propagation and coalescence processes mainly cause rock failures in tunnels. In this study, we focused on the crack initiation, propagation and coalescence process of rock materials containing two pre-existing open cracks arranged in different geometries. During uniaxial compression, wing crack initiation stress, wing crack propagation angle, and crack coalescence stress of Diastone gypsum and Yeosan Marble specimens were examined. And crack initiation, propagation, and coalescence processes were observed. Shear, tensile and mixed (shear+tensile) types of crack coalescence occurred. To compare the experimental results with Ashby & Hallam model, crack coalescence stress was normalized and it generally agreed with the experimental results.

Keywords
Rock bridges
Wing crack
Crack coalescence
Ashby & Hallam model

암석은 지질학적 생성과정으로 인해 많은 역할적 결함을 포함하고 있으며 이러한 결함 사이에는 암석 브릿지가 존재하게 된다. 이러한 암석 브리짓에서의 균열의 전파 및 결합(coalescence)과정은 터널의 안정성에 영향을 미치게 된다. 본 연구에서는 단축압축 하에서 균열의 형상변화에 따른 암석 브릿지에서의 균열의 개시, 전파 및 결합거동 변화를 강화석고의 일종인 Diastone과 여산 대리석 시료에 대해 알아보았다. 하중을 가하면서 날개형 균열 개시응력, 날개형 균열 전파각도, 균열결합 응력을 측정하였으며, 전단, 인장, 혼합형의 3가지 균열결합 유형이 나타났다. 또한, 정규화된 최대강도(normalized peak strength)를 구하여 Ashby & Hallam 모형(1986)의 이론해와 비교, 분석하였다.

키워드
암석 브릿지
날개형 균열
균열결합
Ashby & Hallam 모형

MAIN

  • 1. Introduction

  • 2. Experimental Study

  •   2.1 Test Materials

  •   2.2 Specimen Geometries

  • 3. Ashby & Hallam Model

  • 4. Results

  •   4.1 Wing Crack

  •   4.2 Crack Coalescence

  •   4.2.1 Classification of Crack Coalescence Type

  •   4.2.2 No Crack Coalescence

  •   4.3 Crack Coalescence Stress

  •   4.3.1 The effect of pre-existing angle and bridge angle

  • 5. Conclusions

Acknowledgements

References

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