Journal of Korean Tunnelling and Underground Space Association (한국터널지하공간학회 논문집)

Korean Tunnelling and Underground Space Association (한국터널지하공간학회)
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A study on evaluation of flexural toughness of synthetic fiber reinforced shotcrete

구조용 합성섬유 보강 숏크리트 휨인성 평가에 관한 연구

  • Received : 2019.04.08
  • Accepted : 2019.05.13
  • Published : 2019.05.31
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Abstract

This study deals with shotcrete reinforcing performance according to the amount of synthetic fiber (PP fiber) and proper evaluation method. The shotcrete compressive strength, flexural strength and flexural toughness were tested by setting the mixing amounts of steel fiber ($37.0kg/m^3$) and synthetic fiber (PP fiber) as parameters ($5.0kg/m^3$, $7.0kg/m^3$ and $9.0kg/m^3$). Particularly, circular panel flexural toughness test (Road and Traffic Authority, RTA) was performed to evaluate the shotcrete energy absorption capacity. As a result, the compressive strength and the bending strength of the steel fiber reinforced shotcrete were large, but the flexural toughness of the synthetic fibe (PP fiber) reinforced shotcrete was large. Therefore, synthetic fiber (PP fiber) reinforced shotcrete is considered to have a reinforcing effect comparable to that of steel fiber reinforced shotcrete. Analysis of the relationship between the flexural toughness and the energy absorption capacity of synthetic fiber (PP fiber) reinforced shotcrete revealed that the energy absorbing ability is exhibited at a flexural toughness lower than the allowable standard (3.0 MPa). (Class A: 2.55 MPa = 202J, Class B: 2.72 MPa = 282J, Class C: 3.07 MPa = 403J). As a result of this study, it can be concluded that the actual shotcrete support performance can be evaluated by evaluating the support performance of the shotcrete measured at less than the allowable standard (3.0 MPa) at the actual tunnel site.

본 연구는 구조용 합성섬유(PP섬유) 혼입량에 따른 숏크리트 보강성능과 적정한 평가방법에 관한 것으로, 강섬유($37.0kg/m^3$)와 구조용 합성섬유(PP섬유) 혼입량을 매개변수($5.0kg/m^3$, $7.0kg/m^3$, $9.0kg/m^3$)로 설정하여 숏크리트 압축강도, 휨강도 및 휨인성 시험을 수행하였다. 특히, 판상의 숏크리트 에너지 흡수능력을 평가하기 위하여 원형 패널 휨인성 시험(Road and Traffic Authority, RTA)을 수행하였다. 검토결과, 압축강도 및 휨강도는 강섬유 보강 숏크리트가 다소크나, 실질적인 숏크리트 보강성능를 나타내는 휨인성은 구조용 합성섬유(PP섬유) 보강 숏크리트가 큰 것으로 분석됨에 따라, 강섬유 보강 숏크리트 대비 동등 이상의 보강효과를 발휘하는 것으로 검토되었다. 또한, 구조용 합성섬유(PP섬유) 혼입량에 따른 휨인성 및 에너지 흡수능력 상관관계에 의하면, 보시편 휨인성 시험(KS F 2566)의 허용기준 3.0 MPa이하조건에서 에너지 흡수능력이 발휘(A등급: 2.55 MPa = 202J, B등급: 2.72 MPa = 282J, C등급: 3.07 MPa = 403J)되는 것으로 검토되었다. 국내 터널현장에서 보수적으로 측정되는 강도개념의 숏크리트 휨인성(>3.0 MPa)을 본 연구의 숏크리트 에너지 흡수능력 상관관계로 지보성능을 평가할 경우, 보다 실질적이고 신뢰도 높은 숏크리트 지보성능 평가가 가능할 것으로 판단된다.

Keywords

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Fig. 1. Q-System chart

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Fig. 2. EFNARC-RTA relation

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Fig. 3. Compressive strength test

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Fig. 4. Flexural toughness test

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Fig. 5. RTA test

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Fig. 6. Test sample production view

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Fig. 7. Flexural strength according to fiber content

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Fig. 8. Flexural toughness according to fiber content

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Fig. 9. Steel fiber sample (37.0 kg/m3, m = 0.5%) load-displacement curve

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Fig. 10. Synthetic fiber sample (5.0 kg/m3, m = 0.55%) load-displacement curve

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Fig. 11. Synthetic fiber sample (7.0 kg/m3, m = 0.76%) load-displacement curve

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Fig. 12. Synthetic fiber sample (9.0 kg/m3, m = 1.00%) load-displacement curve

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Fig. 13. Flexural strength-Flexural toughness ratio relation

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Fig. 14. Flexural strength-Residual strength ratio relation

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Fig. 15. Maximum load according to fiber content

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Fig. 16. Energy Absorption Capacity according to fiber content

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Fig. 17. Steel fiber sample (37.0 kg/m3, m = 0.5%) load-displacement curve

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Fig. 18. Synthetic fiber sample (5.0 kg/m3, m = 0.55%) load-displacement curve

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Fig. 19. Synthetic fiber sample (7.0 kg/m3, m = 0.76%) load-displacement curve

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Fig. 20. Synthetic fiber sample (9.0 kg/m3, m = 1.00%) load-displacement curve

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Fig. 21. Flexural toughness - Energy absorbing capacity by fiber reinforcement

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Fig. 22. Flexural toughness - Energy absorption capacity relationships by fiber reinforcement

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Fig. 23. Q-chart (RTA energy absorption capacity)

Table 1. EFNARC-RTA relation energy absorption capacity

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Table 2. Shotcrete formulation table (kg/m3)

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Table 3. Type of sample

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Table 4. Compressive strength test results

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Table 5. Synthetic fiber shotcrete flexural toughness - energy absorption capacity relative grade criterion

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