EGU2011 1821 presentation by S0U2D663


									                                                                                                                  Topography, rock mass strength and pore water pressure
                                                                                                                                                    Jia-Jyun Dong, Yi-Ju Su and Chyi-Tyi Lee
                                                                                                                               Graduate Institute of Applied Geology, National Central University, Jhongli, Taiwan                                                             Abstract number: EGU2011-1821;
                                                                                                                                                                                                                                                                                         Session NH3.10/GM6.2

                                                                   Abstract                                                                                                 Methodology - Slope performance curve                                                                       Result (IV)
                                                                                                                                                       Rock mass                                    Hoek and Brown                 Slope stability analysis               Verification of the slope performance curves
Relief is a fundamental landscape reflecting the influence of uplift and erosion. Contrary to the
traditional concept that the relief is dominated by incision, several researches indicate that the                                                    classification                                Failure Criterion                                                                         (Taheri and Tani, 2010)
landscape-scale material strength play an important role on the landform process. However, it is                                                                                            GSI, mi=9,                                                                                                       Back calculated
difficult to obtain a representative strength parameters based on laboratory rock tests. Slope                                                              RMR                            (σci)=35 MPa                                                                                                      GSI=30~40
height and slope angle were frequently used to infer the strength of rock mass. In this research, a
series of slope response curves will be proposed to constrain the rock mass strength. Non-linear                                                             Mohr-Coulomb Failure Criterion                                                                                        Real GSI                  Real
Hoek-Brown failure criterion will be incorporated into the proposed model where the linear                                                                                                                                       FS=1                                                                        GSI=28~33
Mohr-Coulomb failure envelop seems oversimplified. Meanwhile, the influence of pore water
                                                                                                                                                        RMR  20     25 1  0.01RMR           c  3.625RMR
pressure on the slope stability is considered. Consequently, the strength of rock mass could be
                                                                                                                                                        RMR  20     1.5RMR
inferred from the topography. Cases including stable and failed rock slopes with reported slope
height and slope angle are used to validate the proposed model. The result shows that the
strength parameter of rock mass could be reasonably inferred from the topography if the pore                                                                                                                                      Slope performance curve
pressure can be evaluated.

                                                                                                                                                                           Result (I)                                                 Result (II)
                                                                Motivation                                                                             RMR-based slope performance curves                        GSI-based slope performance curves – dry slope
  Importance of rock mass strength
                                                                                                                          Evert Hoek, 2000.
                                                                                                                          Practical rock
                                                                                                                                                                                                                          mi=5                                                                                Back calculated
   Evert Hoek, 2000. Practical rock engineering                                                                           engineering
                                                          Bye, A. R., Bell, F. G., 2001. Stability assessment and slope
                                                          design at Sandsloot open pit, South Africa, International                                                                                                                                                                                           GSI=40
                                                          Journal of Rock Mechanics & Mining Sciences, 38, 449-466.

                                                                                                                                                                                                                        σci =250MPa              σci =35MPa

  How to get representative rock mass strength?                                                                                                                                                                                                              σci=3MPa
                                                                                                                                “Scale effect” of
    – Laboratory tests                            Scale effect                                                                                        Measured slope angles and slope heights                                                                                                                Back calculated
                                                                                                                               rock mass strength                                                                                                                                                             Ru=0.3~0.6.
    – In situ tests                               Scale effect
    – Back analysis                               Feasible !!
                                                                                                                                                                                                                        mi=33                        mi=9
 Topography data from MOLA + rock mass classification system RMR

                                                                                                                                                                                                                                      Result (III)
                                                                                                                                                                                                                  GSI-based slope performance curves – wet slope
                                                                                                   Wallrock: 50<RMR<65
                                                                                                   Interior deposits: 30<RMR<55
                                                                                                                                                                                                                                 mi=9, σci = 35MPa
                                                                                                                                                                                                                                                                          The strength of rock mass can be well constrained
                                                                                                                                                                                                                                                                           by the topography.
                                                                                                                                                     Back calculated RMRs are significant lower                                                                           Pore pressure distributed in the rock slope is
                                                                                                                                                     than the field evaluated RMRs. Effect of                                                                              essential for back calculating the strength.
   Schultz, 2002                                                                                                                                                                                                         Ru= u/σv=0                  Ru=0.3
                                                                                                                                                     pore pressure should be considered.                                                                                  The influence of earthquake on the topography
  Slope height vs. Slope angle of wallrock and interior deposits in Valles Marineris                                                                                                                                                                                       needs to be studied.

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