Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Improvement of Lift-off Tests via Field Evaluation of Residual Load in Ground Anchor

현장 잔존긴장력 평가를 통한 리프트오프 시험 방법 개선

  • Song, minkwon (Dept. of Civil & Environmental Engrg., Dankook Univ.) ;
  • Park, Seong-yeol (Dept. of Civil & Environmental Engrg., Dankook Univ.) ;
  • Lee, Sangrae (Korea Expressway Corporation Research Institute) ;
  • Cho, Wanjei (Dept. of Civil & Environmental Engrg., Dankook Univ.)
  • 송민권 (단국대학교 토목환경공학과) ;
  • 박성열 (단국대학교 토목환경공학과) ;
  • 이상래 (한국도로공사 도로교통연구원 안전연구실) ;
  • 조완제 (단국대학교 토목환경공학과)
  • Received : 2019.04.19
  • Accepted : 2019.05.03
  • Published : 2019.05.31
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Abstract

At present, the ground anchor method is commonly applied to securing the slope stability in Korea. The ground anchor is reported to decrease in tensile load due to aging and environmental influences with time such as corrosion, relaxation, creep and so on. In Korea, the lift-off test is performed for the periodic inspection or cases when the symptoms of deterioration on anchors and the residual tensile load of the anchors is checked. However, the current lift-off test standard (MOLIT, 2010) is not fully specified in details. In this study, the factors affecting the lift-off test were investigated based on the previous research and foreign standards and lift-off tests were performed with consideration for the loading and unloading cycle, load increment method, and tensioning tendon method. Based on the results, this paper proposes improved testing and evaluation procedures of the lift-off test considering the workability and time limits in the field.

현재 국내에서는 비탈면의 안정성 확보를 위해 그라운드 앵커공법을 적용하고 있다. 그라운드 앵커는 시간이 지남에 따라 노후화 및 환경적 영향에 의한 부식, 릴렉세이션, 크립 등으로 긴장력 감소현상이 발생하며, 이로 인해 앵커의 긴장력은 설계앵커력 이하로 감소할 가능성을 내포하고 있다. 이에 국내에서는 정기적인 점검 시 또는 이상 징후가 발생한 앵커를 대상으로 리프트오프 시험을 수행하여 앵커의 잔존긴장력을 확인하고 있으나, 현재 국내 리프트오프 시험기준(국토해양부, 2010)은 수행 및 평가방법이 자세히 명시되어 있지 않은 실정이다. 이에 본 연구에서는 선행연구들을 바탕으로 하중 재하 제하 사이클, 하중 증분방법, 긴장재 긴장 방법 등을 고려하여 리프트오프 시험을 수행하였으며 현장에서의 시공성과 시간적 제한을 고려하여 효율적인 리프트오프 시험 및 평가방법 개선안을 제시하였다.

Keywords

GJBGC4_2019_v35n5_43_f0001.png 이미지

Fig. 1. Evaluation of residual load by lift-off test

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Fig. 2. Load-displacement curve for cycle (Fujiwara and Sakai, 2016)

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Fig. 3. Equipment diagram for lift-off test using different tensioning equipment

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Fig. 4. Result of lift-off test with regard to initial load, load increment method, loading cycle

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Fig. 5. Result of lift-off test using different tensioning equipment

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Fig. 6. Lift-off test method proposed in this study

Table 1. Load increment, load and displacement measurement interval for lift-off test (Ground Anchor Technology Association, 1997)

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Table 2. Load increment, load and displacement measurement interval for lift-off test proposed in this study

GJBGC4_2019_v35n5_43_t0002.png 이미지

References

  1. British Standards Institution (1989), "British Standard Code of Practice for Ground anchorages", BS 8081.
  2. Civil Engineering Department Hong Kong (1997), "Model Specification for prestressed ground anchors", Geotechnical Control Office, GEOSPEC1.
  3. Deutshe Industrie Normen (1990), "Ground Anchorages Design, construction and testing", DIN-4125.
  4. Fujiwara, Y. and Sakai, T. (2016), "A Study of a Lift-off Test Method for Ground Anchors", Journal of JSCE, Vol.4, pp.106-117. https://doi.org/10.2208/journalofjsce.4.1_106
  5. Ground Anchor Technology Association (1997), "Design.Construction Guideline for Ground Anchor".
  6. Kim, N.K. (2001), "Pullout Capacity of Ground Anchors in Weathered Soil", Journal of The Korean Geotechnical Society, Vol.17, No.4, pp.231-239.
  7. Korea Expressway Corporation (2016), "A Survey on the Application Actual Condition and Establishment of Performance Improvement countermeasure of Permanent Anchor for Ground Reinforcement", In Korean.
  8. Ministry of Land, Transport and Maritime Affairs (2010), "Ground Anchor Design.Construction and Maintenance Manual", In Korean.
  9. Post Tensioning Institute (1996), "Recommendations for Prestressed Rock and Soil Anchors, 3rd ed", Post Tensioning Institute.
  10. Sabatini, P.J., Pass, D.G., and Bachus, R.C. (1999), "Geotechnical Engineering Circular NO. 4 Ground Anchors and Anchored systems", U.S Department of Transportation, FHWA-IF-99-015.

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