1. Hieu Toan NGUYEN Jean-Alain FLEURISSON Roger COJEAN Evaluation of topographic site effect in slope stability under dynamic loading

2. PLAN DE LA PRESENTATION

3. VEESD 2013 Page 3 1. Introduction  Topography site effect  Cause: the irregularities of the morphology (slope, ridge, cliff...) → the interference of the incident and the reflected waves  Consequence: the spatial, spectral and temporal modifications of the seismic signal  Aggravation of the earthquake damages and the slope instabilities Las Colinas landslide triggered by the earthquake 13-01-2001 (Mw=7.6) Amplification De-amplification Incident waves Amplification De-amplification

4. VEESD 2013 Page 4 1. Introduction  Eurocode 8 (2005)  Slope belong to the two-dimensional topographic irregularities: long ridges, cliff…  Slope height ≥ 30m  Slope angle ≥ 15°  French paraseismic code PS-92  Remarks  Do not take into account the role of the geologic and seismic conditions of slope.  Do not take into account the characteristic of the seismic signal.  Study purpose  Identify the factors influencing the slope topographic site effect.  Determine the relationships between these factors and this phenomenon.  Provide a simple method to quantify this effect. ConfigurationsAmplification factor Isolated cliffs and slopesS T ≥1.2 Ridges with crest width significantly less than the base width <30° S T ≥1.2 ≥30° S T ≥1.4

5. VEESD 2013 Page 5  Interpretation criteria  Amplifications factors  Proportion by area of the amplified zones  Dimension of the amplified zone at the slope crest: Hx, Dxc 2a. Methodology outline  Mesh size   N=30÷100  Numerical error < 3%  Boundary conditions  Free Field  Quiet boundary  Seismic excitation  SV wave, sinusoidal signal  PGA=0.4g, F=0.5÷10Hz 20m  H 5H H/tan(  15H+H/tan(  Quiet boundary Free Field 2H² S 1 U S 2 U S 3 U S 4 S 1 U S 2 U S 3 1 3 4 2 Dxc Hx   pS AS pS A Ax Ay 2H H

6. VEESD 2013 Page 6 2b. Impact of the dimensionless frequency  Important parameters in a site effect study  Step-like slope with homogeneous, isotropic and elastic material Morphologic parameters: H,  Geologic parameters : E,,  Seismic characteristic parameter:   Sinusoidal seismic signal Amplitude : PGA Frequency : F Shaking duration : t  Dimensionless frequency ()  Integrated parameters : H, E, F, 

7. VEESD 2013 Page 7 2b. Impact of the dimensionless frequency  Parametric analyses  Change the value of 2 of the 5 parameters (H, E, F,  ) each time  10 couples  Change 4 times for each couple  40 cases  Results  Evaluate the coefficient of variation (standard deviation/mean)  Conclusions  Ax=f(H)  Ay=f(H, )  pS=f(H)  Hx=f(H)  Dxc=f(H, ) Couple of varying parameters[H,F][H,E] [H, ][H,  ] [F,E] [F, ][F,  ][E, ][E,  ][,  ] Numerical simulation number12345678910 H,EH,F 1 3 4 2 Dxc Hx   pS AS pS A Ax Ay

8. VEESD 2013 Page 8 2b. Impact of the dimensionless frequency H=25mH=50mH=200mH=100m H=25mH=50mH=200mH=100m =0.2=0.25=0.35=0.3 H=40mH=80m

9. VEESD 2013 Page 9 0.15 2b. Impact of the dimensionless frequency  Parametric analyses  Same geomorphologic condition   =0.05÷1.0 (  =0.05)  Conclusions  Horizontal amplification o  ≤0.5 : amplification zones along the free surface  ≤0.15 : one amplified zone, at crest  >0.15 : many amplified zones, at crest and behind the crest o  >0.5 : additional amplification zones inside the slope mass  Vertical amplification o  ≤0.5 : highest amplified zone located along the slope o  >0.5 : highest amplified zone located at the crest =0.05=0.4=0.2=0.1=0.6 0.5

10. VEESD 2013 Page 10  Parametric analyses  Slope angle  =30÷80  Results  Conclusions  The amplification factors (Ax, Ay) increase with an increase of the slope angle  Dxc is not dependent on the slope angle  Other criteria (pS A, pS AS, Hx), the interaction between  and  should be considered 2c. Impact of the slope angle 1 3 4 2 Dxc Hx   pS AS pS A Ax Ay Tendency of the given criterion when  increases Increase (I) Decrease (D) Non dependent (ND)

11. VEESD 2013 Page 11 3. Conclusions and perspectives H  AxDNDII Ay I (  ≤0.3) D (  >0.3) DI I  ≤0.5: highest amplified zone located along the slope  >0.5: highest amplified zone located at the crest pS A pS AS D (  ≤0.15) ND (  >0.15) ND I (  ≤0.15) D (  >0.15) D  ≤0.5: amplification zones along the free surface *  ≤0.15: one amplified zone, at crest *  >0.15: many amplified zones behind the crest  >0.5: additional amplification zones inside the slope mass Hx D (  ≤0.2) ND (  >0.2) ND I (  ≤0.35) ND (  >0.35) D DxcDINDD  Conclusions  Important role of the dimensionless frequency parameter  Summary table of the relationships between the affecting factors and the interpretation criteria  Graphs to estimate Ax, Ay, pS A, pS AS, Hx, Dxc as a function of  (  =0.05÷0.4) and  (  =30÷80°)  Perspectives  Improve the graphs by extending the value range of  and by integrating H and  Develop a calculation method applicable to a real seismic signal with a large frequency band.  Extend the study to the cases of the slopes with the more complex and more realistic geomorphologic conditions

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