KSCE Journal of Civil and Environmental Engineering Research (대한토목학회논문집)

Korean Society of Civil Engeneers (대한토목학회)
권호 표지
DOI QR코드

DOI QR Code

Estimation of the Shaft Resistance of Rock-Socketed Drilled Shafts using Geological Strength Index

GSI를 이용한 암반에 근입된 현장타설말뚝의 주면저항력 산정

  • 조천환 (삼성물산(주) 건설부문 T.A.팀) ;
  • 이혁진 (홍익대학교 대학원 토목공학과)
  • Received : 2005.09.21
  • Accepted : 2005.11.08
  • Published : 2006.01.31
Download PDF
⟨ Previous Next ⟩

Abstract

It is common to use the unconfined compressive strength (UCS) of intact rock to estimate the shaft resistance of rock socketed drilled shaft. Therefore the most design manuals give a guide to use the UCS of rock core to estimate the shaft resistance of rock-socketed drilled shaft. Recently, however the design manuals for highway bridge (KSCE, 2001) and of AASHTO (2000) were revised to use the UCS of rock mass with RQD instead of the UCS of rock core so that the estimated resistance could be representative of field conditions. Questions have been raised in application of the new guide to the domestic main bed rock types. The intrinsic drawbacks in terms of RQD were comprised in the questions, too. As the results, in 2002 the new guide in the design manual for highway bridge (KSCE, 2001) were again revised to use the UCS of rock core to estimate the shaft resistance of rock-socketed drilled shafts. In this paper, various methods which can estimate the UCS of rock mass from intact rock core were reviewed. It seems that among those, the Hoek-Brown method is very reliable and practical for the estimation of the UCS of rock mass from rock cores. As the results, using the Hoek-Brown failure criterion a modified guide for the estimation of the shaft resistance of rock-socketed drilled shafts was suggested in this paper. Through a case study it is shown that the suggested method gives a good agreement with the measured data.

대부분의 설계지침서에서는 암반에 근입된 현장타설말뚝의 주면저항력을 산출하기 위하여 암석의 일축압축강도를 사용한다. 그러나 최근에 도로교 설계기준 해설(대한토목학회, 2001)과 AASHTO 설계지침서(2000)에서는 현장조건을 보다 잘 반영할 수 있도록 RQD를 적용하여 산출한 암반의 일축압축강도를 사용하도록 개정되었다. 그런데 RQD를 이용하여 암반의 일축압축강도를 산정하는 식을 국내의 주요 기반암에 적용하는 데에 문제가 제기되었고, 여기에는 RQD 자체의 문제점, 즉 지하수, 절리면 상태 등을 반영하지 못한다는 점도 포함되었다. 결국 도로교 설계기준 해설(2001)은 암석의 일축압축강도를 이용하여 주면저항력을 산정하는 방법으로 다시 개정되었다(한국도로공사, 2002). 본 연구에서는 암석의 일축압축강도와 현장 암반의 일축압축강도를 연관시키는 수단으로 제시되어 있는 기존의 여러 방법을 비교 검토하였으며, 이 가운데 신뢰도가 있는 것으로 평가되고 있는 Hoek-Brown 파괴 규준을 이용하여 암반의 일축압축강도 추정식을 제시하였다. 또한 이를 이용하여 암반에 근입된 현장타설말뚝의 주면저항력 예측 방법을 제안하였다. 제안된 방법은 현장타설말뚝의 재하시험 데이터를 이용하여 기존의 여러 방법으로 구한 주면저항력과 비교한 결과 신뢰도가 있음을 알 수 있었다.

Keywords

References

  1. 대한토목학회(2001) 도로교 설계기준 해설(하부구조편)
  2. 양형식(1992) 국내 주요암석의 파괴조건계수, 한국자원공학회지 한국자원공학회,Vol .29 , pp. 91-102
  3. 장병환, 양형식(1999) 암반구조물의 수치해석을 위한 입력자료의 비교분석, 터널과 지하공간, 한국암반공학회지, 한국암반공학회, Vol. 9, pp. 221-229
  4. 전경수(2000) 풍화암에 근입된 현장타설말뚝의 연직 및 횡방향 지지거동 분석, 박사학위논문. 서울대학교
  5. 조천환, 이명환, 조영훈, 유한규, 박언상(2002) 암반에 근입된 현장타설말뚝의 설계 현황, 암반에 근입된 현장타설말뚝의 설계세미나, pp. 29-52
  6. 한국도로공사(1 995) 도로공사 표준 시방서
  7. 한국도로공사 (2002) 암반에 근입된 현장타설말뚝 설계기준 수립
  8. 한국지반공학회 (2003) 구조물 기초 설계기준 해설집
  9. AASHTO (2000) Standards Specifications for Highway Brifges, American Association of State Highway and Transportation Officials.
  10. Bieniawski, Z. T. (1974) Estimating the strength of rock materials, J. S. Afr. Inst. Min. Metall. Vol. 74, No.8, pp. 312-320
  11. Bieniawski Z. T. (1976) Rock mass classification in rock engineer..ing. In Exploration for rock Engineering, Proc. of the Symp.(ed. Z. T Bieniawski), Vol. 1, pp. 97-106
  12. Bieniawski, Z. T (1989) Engineering Rock Mass Classification, John Wiley & Sons, New York, USA
  13. Canadian Geotechnical Society (1992) Foundation Engineering Manual(3rd. ed.), BiTech Publishers, Vancouver, Canada
  14. Carter, J. P. and Kulhawy, F. H. (1987) Analysis and Design of drilled shaft foundations socketed into rock, 1493-4, Cornell University, Ithaca, New York
  15. FHWA (1999) Drilled Shafts : Construction Procedures and Design Methods, National Highway Institute
  16. GEO (1996) Pile Design and Construction, Geotechnical Engineering Office, Hongkong
  17. Hoek, E. (1994) Strength of rock and rock masses, ISRM News Journal, Vol. 2, No.2, p. 4- 16
  18. Hoek, E. and Brown E.T (1997) Practical estimates of rock mass strength. Intnl. J Rock Mech. & Mining Sci. & Geomechanics Abstracts. Vol. 34, No.8, p. 1165- 1186 https://doi.org/10.1016/S1365-1609(97)80069-X
  19. Hoek, E., Carranza-Torres, C.T., and Corkum, B. (2002) HoekBrown fialure criterion - 2002 edition. Proc. North American Rock Mechanics Society meeting, Toronto, July
  20. Hoek, E., Kaiser, P.K., and Bawden. W.F. (1995) Support of underground excavations in hard rock. Rotterdam: Balkema
  21. Hoek, E., Marinos, P., and Benissi, M. (1998) Applicability of the Geological Strength Index(GSI) classification for very weak and sheared rock masses. The case of the Athens Schist Formation. Bull. Engg. Geol. Env. Vol. 57, No.2, pp. 151-160 https://doi.org/10.1007/s100640050031
  22. Hoek, E., Wood, D., and Shah, S. (1992) A modified Hoek-Brown criterion for jointed rock masses. Proc. rock. characterization, symp. Int. Soc. Rock Mech.: Eurock '92, (J.Hudson ed.). pp. 209-213
  23. Horvath, KG., Kenney, TC., and Kozicki, P. (1983) Methods of Improving the Performance of Drilled Piers in Weak Rock, Canadian Geotechnical Journal, Vol. 20, pp. 758-772 https://doi.org/10.1139/t83-081
  24. Laubscher, D. H. (1984) Design Aspects and Effectiveness of Support Systems in Different Mining Conditions, Trans. Inst. Min. Metall. Vol. 93, pp. A70-A81
  25. Marinos, P.G. and Hoek, E. (2000) GSI: A Geological friendly tool for rock mass strength estimation, Proceedings of the International Conference on Geotechnical & Gological Engineering(GeoEng 2000) Technomic Publishing Co. Inc., pp. 1422-1440, Melbourne, Australia
  26. Marinos, P.G. and Hoek, E. (2001) Estimating the geotechnical properties of heterogeneous rock masses such as flysch, Bull. Engg. Geol. Env. Vol. 60. pp. 85-92 https://doi.org/10.1007/s100640000090
  27. NAVFAC (1986) Foundations and Earth Structures. Design Manual. Department of Navy, Naval Facilities Engineering Command.
  28. Rocscience Inc. (2002) RocLab User's Guide
  29. Stille, H., T Groth, and A. Fredriksson (1982) FEM Analysis of Rock Mechanics Problems by JOBFEM, Swedish Rock Engineering Research Foundation Publication, No. 307, pp. 1-8
  30. Yudhbir (1983) An empirical failure criterion for rock masses, Proc. 5th Int. Cong. Rock Mechanics, ISRM, Melbourne, pp.97-133