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Geotechnical and Geological Engineering

, Volume 36, Issue 4, pp 1975–1989 | Cite as

Selecting Equivalent Strength for Intact Rocks in Heterogeneous Rock Masses

  • Mahmoud Behnia
  • Ahmad Rahmani Shahraki
  • Zabihallah Moradian
Original Paper

Abstract

Many surface and underground structures are constructed in heterogeneous rock formations. These formations have a combination of weak and strong rock layers. Due to the alternation of the weak and strong layers, selecting the equivalent and appropriate geomechanical parameters for these formations is challenging. One of these problems is choosing the equivalent strength (i.e., uniaxial compressive strength) of intact rock for a group of rocks. Based on the volume of weak and strong parts and their strength, the equivalent strength of heterogeneous rocks changes. Marinos and Hoek (Bull Eng Geol Environ 60(2):85–92, 2001) presented the “weighted average method” for defining the uniaxial compressive strength (UCS) of heterogeneous rock masses based on the volume of weak and strong parts. Laubscher (1977) used the volume ratio of the strength of a weak part to a strong part (UCS weak/UCS strong) to determine the equivalent strength. In this study, the two methods are compared and their validity is evaluated by experimental data and numerical analyses. The geomechanical parameters of two heterogeneous formations (Aghajari and Lahbari) in the west of Iran were estimated using these methods. The results of the present study obtained through numerical analyses using particle flow code are compared with those of previous studies and discussed. Laboratory and numerical results show UCS decrease and approach to weak strength with an increasing in volume of weak part. When strength ratio of strong to weak rock increase, equivalent strength decrease more severely. The findings show that Laubscher’s method gives more appropriate results than the weighted average method.

Keywords

Heterogeneous rocks Uniaxial compressive strength Weighted average method GSI Geomechanical parameters Numerical analysis PFC 

References

  1. Budetta P, Nappi M (2011) Heterogeneous rock mass classification by means of the geological strength index: the San Mauro formation (Cilento, Italy). Bull Eng Geol Environ 70(4):585–593CrossRefGoogle Scholar
  2. Cho NA, Martin CD, Sego DC (2007) A clumped particle model for rock. Int J Rock Mech Min Sci 44(7):997–1010CrossRefGoogle Scholar
  3. Duffaut P (1981) Structural weaknesses in rocks and rock masses tentative classification and behaviour. ISRM International Symposium, International Society for Rock MechanicsGoogle Scholar
  4. Goodman RE (1993) Engineering geology: rock in engineering construction. Wiley, New YorkGoogle Scholar
  5. Hoek E, Brown ET (1997) Practical estimates of rock mass strength. Int J Rock Mech Min Sci 34(8):1165–1186CrossRefGoogle Scholar
  6. International Society for Rock Mechanics (1977) Commission on standardization of laboratory and field tests. Committee on Laboratory Tests, Nieble CM. Suggested method for petrographic description of rocks. ISRMGoogle Scholar
  7. James G, Wynd J (1965) Stratigraphic nomenclature of Iranian oil consortium agreement area. AApG Bull 49(12):2182–2245Google Scholar
  8. Laubscher D (1977) Geomechanics classification of jointed rock masses-mining applications. Trans Instn Min Metall 86:A1–A8Google Scholar
  9. Liang WG, Yang CH, Zhao YS, Dusseault MB, Liu J (2007) Experimental investigation of mechanical properties of bedded salt rock. Int J Rock Mech Min Sci 44(3):400–411CrossRefGoogle Scholar
  10. Lydzba D, Pietruszczak S, Shao JF (2003) On anisotropy of stratified rocks: homogenization and fabric tensor approach. Comput Geotech 30(4):289–302CrossRefGoogle Scholar
  11. Mandrone G (2006) Engineering geological mapping of heterogeneous rock masses in the Northern Apennines: an example from the Parma Valley (Italy). Bull Eng Geol Environ 65(3):245–252CrossRefGoogle Scholar
  12. Marinos V (2010) New proposed GSI classification charts for weak or complex rock masses. Bull Geol Soc Greece 43(3):1248–1258CrossRefGoogle Scholar
  13. Marinos V (2014) Tunnel behaviour and support associated with the weak rock masses of flysch. J Rock Mech Geotech Eng 6(3):227–239CrossRefGoogle Scholar
  14. Marinos P, Hoek E (2001) Estimating the geotechnical properties of heterogeneous rock masses such as flysch. Bull Eng Geol Environ 60(2):85–92CrossRefGoogle Scholar
  15. Marinos VI, Marinos P, Hoek E (2005) The geological strength index: applications and limitations. Bull Eng Geol Environ 64(1):55–65CrossRefGoogle Scholar
  16. Marinos V, Fortsakis P, Prountzopoulos G (2006) Estimation of rock mass properties of heavily sheared flysch using data from tunnelling construction. In: IAEG2006, paper (314)Google Scholar
  17. Marinos P, Marinos V, Hoek E (2007) Geological strength index (GSI). A characterization tool for assessing engineering properties for rock masses. In: Romana M, Perucho A, Olalla C (eds) Underground works under special conditions. Taylor and Francis, Lisbon, pp 13–21Google Scholar
  18. Mohamed Z, Mohamed K, Gye Chun C (2008) Uniaxial compressive strength of composite rock material with respect to shale thickness ratio and moisture content. Electron J Geotech Eng 13:1–10Google Scholar
  19. Motiei H (1993) Stratigraphy of Zagros. Treatise Geol Iran 1:60–151Google Scholar
  20. Pepe G, Piazza M, Cevasco A (2015) Geomechanical characterization of a highly heterogeneous flysch rock mass by means of the GSI method. Bull Eng Geol Environ 74(2):465–477CrossRefGoogle Scholar
  21. Read J, Stacey P (2009) Guidelines for open pit slope design. CSIRO publishing. Leiden, NetherlandsGoogle Scholar
  22. Tien YM, Kuo MC, Juang CH (2006) An experimental investigation of the failure mechanism of simulated transversely isotropic rocks. Int J Rock Mech Min Sci 43(8):1163–1181CrossRefGoogle Scholar
  23. Tsiambaos G (2010) Engineering geological behaviour of heterogeneous and chaotic rock masses. Bull Geol Soc Greece 43(1):183–195CrossRefGoogle Scholar
  24. Tziallas GP, Saroglou H, Tsiambaos G (2013) Determination of mechanical properties of flysch using laboratory methods. Eng Geol 166:81–89CrossRefGoogle Scholar
  25. Vlasov A, Merzlyakov V (2004) Analysis of test results of composite specimens modeling rock. Soil Mech Found Eng 41(6):191–199CrossRefGoogle Scholar
  26. Yue K, Olson JE, Schultz RA (2016) Calibration of stiffness and strength for layered rocks. In: 50th US rock mechanics/geomechanics symposium, American Rock Mechanics AssociationGoogle Scholar

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Mahmoud Behnia
    • 1
  • Ahmad Rahmani Shahraki
    • 1
  • Zabihallah Moradian
    • 2
  1. 1.Department of Mining EngineeringIsfahan University of TechnologyIsfahanIran
  2. 2.Department of Civil and Environmental Engineering and Earth Resources Lab (ERL)Massachusetts Institute of Technology (MIT)CambridgeUSA

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