The strength of rock mass can be well constrained by the topography.

1. 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 Result (IV) Methodology - Slope performance curve Abstract 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 landscape-scale material strength play an important role on the landform process. However, it is difficult to obtain a representative strength parameters based on laboratory rock tests. Slope 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 Hoek-Brown failure criterion will be incorporated into the proposed model where the linear Mohr-Coulomb failure envelop seems oversimplified. Meanwhile, the influence of pore water pressure on the slope stability is considered. Consequently, the strength of rock mass could be 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 pressure can be evaluated. • Verification of the slope performance curves Rock mass classification Hoek and Brown Failure Criterion Slope stability analysis (Taheri and Tani, 2010) GSI, mi=9, (σci)=35 MPa Back calculated GSI=30~40 Real GSI=28~33 RMR Mohr-Coulomb Failure Criterion Real GSI FS=1 α=? Slope performance curve Result (I) Result (II) Motivation • GSI-based slope performance curves – dry slope • RMR-based slope performance curves • Importance of rock mass strength mi=5 Evert Hoek, 2000. Practical rock engineering Back calculated GSI=40 Real GSI=46~50 Evert Hoek, 2000. Practical rock engineering Bye, A. R., Bell, F. G., 2001. Stability assessment and slope design at Sandsloot open pit, South Africa, International Journal of Rock Mechanics & Mining Sciences, 38, 449-466. σci =35MPa σci =250MPa • How to get representative rock mass strength? • Laboratory tests • In situ tests • Back analysis σci=3MPa “Scale effect” of rock mass strength Back calculated Ru=0.3~0.6. • Measured slope angles and slope heights Scale effect Scale effect 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. • Pore pressure distributed in the rock slope is essential for back calculating the strength. • The influence of earthquake on the topography needs to be studied. Back calculated RMRs are significant lower than the field evaluated RMRs. Effect of pore pressure should be considered. Schultz, 2002 Ru= u/σv=0 Ru=0.3 Slope height vs. Slope angle of wallrock and interior deposits in Valles Marineris