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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 α=? 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. Real GSI=46~50 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 Conclusions 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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