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Analysis of a deep seated slope failure in the Alps
Tom Schanz, Maria Datcheva & Anke Spickermann, Laboratory of Soil Mechanics
Laboratory of Soil Mechanics

Acknowled

gements Michael Moser (Universit?t Erlangen) Yves Bonanomi (Sedrun, Schweiz) Florian Amann Elektrowatt AG, Zurich) Peter Gu?mann (KEM)
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

Contents 1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

1. Introduction
? location ? methods of field measurements and observations ? processes and mechanisms influencing the slope instability ? objective: obtain the geometry and the dimensions of the potential failure mass ? rock mass run-off after four main scenarios
1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary
Numerik in der Geotechnik

AK 1.6 16-17 October 2003, Weimar

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

Maximum deformation measured: measured: 85cm/year 85cm/year

?
60 50
Elevation [m]

40 30 20 10 0 -10

GPS High precision measuring tape
0 10 20 30 40 50 60 Distance [m] 70 80 90 100

Tacheometric survey
Numerik in der Geotechnik

AK 1.6 16-17 October 2003, Weimar

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

α > (90° - β) + ? α ... Inclination of slope β ... Inclination of joints ? ... Friction angle of joints

Flexural toppling

Blocky toppling

Flexural blocky toppling

Sketches taken from different literature
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

Fig. 1.1: Original situation

Fig. 1.2: Scenario 3 3 322 250 m?

Amann & Moser (2002) Fig. 1.3: Scenario 2 4 886 853 m? Fig. 1.4: Scenario 1 15 095 617 m?

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

main scenarios (Bonanomi, Amann & Moser, 2002) scenario 1 = 15 095 617 m? scenario 2 = 4 886 853 m? scenario 3 = 3 322 250 m? scenario 4 = 170 000 m?

2400

2300

2200

2100

2000

1900

1800

Szenario 4 Szenario 2 Szenario 1

1700

1600

1500

1400 171400

171600

171800

172000

172200

172400

172600

172800

173000

173200

Szenario 3
Fig. 1.5: Scenario 1 – 4 , central region of the slope
AK 1.6 16-17 October 2003, Weimar

Fig. 1.6:

Failure surface scenario 1 Failure surface scenario 2 Failure surface scenario 3 Failure surface scenario 4

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

Size and location of failure mass are needed for this type of annalysis?

Fig. 1.7: Visualisation of a Run-Out Analysis, first results Lagrangian solution of St. Venant`s equation (Meier, Schanz & Hungr, 2003)
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

2. Geological situation
? profil geometrie

length = 1012 m height = 595 m ? material → mineralogical composition → weathering → joints structure ? loading → post glacial unloading
Amann & Moser (2002) Fig. 2.1: Isolines of displacements 1999, location of the profile studied
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

1. Joints (micro-meso) Smeared approach 2. Disturbed zones (macro) Discrete approach

Fig. 2.2: Analysed cross section of the slope (Amann & Moser, 2002)

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

3. Main assumptions

? Distribution and thickness of weathered zones ? Material properties ? Initial stresses – geological history
1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

? Depth of weathered zones?

Fig. 3.1: Geological situation (rock mass units, orientation of joints, current topography)
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

Fig. 3.2: Scheme of the two main dip directions of the joints

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary
Numerik in der Geotechnik

AK 1.6 16-17 October 2003, Weimar

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

? Material properties?
Tab. 3.1: Summary of the used material properties

material zones Young's modulus [MPa] density [kg/m?] friction angle [°] cohesion [MPa] friction angle [°] (degradation) cohesion [MPa] (degradation) dilatancy [°] (degradation) Poisson's ratio

granite-gneiss 9000 2500 46 1,2 35

gneiss 8000 2500 44 1 35

weak rocks 1000 2500 27 0 27

quartzite 12000 2500 45 2 35

disturbed zones 3000 2500 29 0 29

0

0

0

0

0
1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

5 0,25

5 0,25

1 0,25

5 0,25

1 0,25

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

? Determination of initial stresses – geological history?

Fig. 3.3: Initial state

Fig. 3.4: Ice replaces rock on layer 1

Fig. 3.5: Ice replaces rock on layer 2

Fig. 3.6: Ice replaces rock on layer 3

Fig. 3.7: Ice replaces rock on layer 4

Fig. 3.8: Removing ice layer 1

Fig. 3.9: Removing ice layer 2

Fig. 3.10: Removing ice layer 3

Fig. 3.11: Removing ice layer 4
AK 1.6 16-17 October 2003, Weimar

Fig. 3.12: Current state of the slope
Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

4. Numerical modelling
? FEM ? KEM → finite element method (PLAXIS) → Kinematic Element Method (Gu?mann)

? Finite element continuum model → 3D anisotropic continuum → Macro: disturbed zones - interface elements → Meso-micro: jointed rock model ? Discretization → x-y-dimension: 2000 x 1000 m → 4 slices x 75 m = 300m in z-direction → 4 x 2089 = 8356 15-node wedge elements

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

? FEM

material zones Young's modulus [MPa] density [kg/m?] Poisson's ratio Rinter joint set 1 friction angle [°] cohesion [MPa] dilatation angle [°] joint set 2 friction angle [°] cohesion [MPa] dilatation angle [°]

granite-gneiss 9000 2500 0,25 0,6 α1 = 85° , 46 1,2 16 α1 = 85° , 46 1,2 16

gneiss 8000 2500 0,25 0,6 α2 = 160° 44 1 14 α2 = 30° 44 1 14

weak rocks 1000 2500 0,25 0,6

quartzite 12000 2500 0,25 0,6

27 0 1

45 2 15

27 0 1

45 2 15

Tab. 4.1: Material properties of calculation phase 1 ... 9

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

Tab. 4.2: Material properties of calculation phase 10

material zones

granite- granite-gneiss granite- gneiss weak quartzite gneiss slightly gneiss rocks weathered weathered 9000 2500 0,25 0,6 46 1,2 16 46 1,2 16 9000 2500 0,25 0,3 35 0 5 35 0 5 9000 2500 0,25 0,01 35 0 5 35 0 5 8000 2500 0,25 0,6 44 1 14 44 1 14 1000 2500 0,25 0,6 27 0 1 27 0 1 12000 2500 0,25 0,6 45 2 15 45 2 15

Fig. 4.1: Decrease of the interface strength reduction factor Rinter

Young's modulus [MPa] density [kg/m?] Poisson's ratio Rinter friction angle [°] cohesion [MPa] dilatation angle [°] friction angle [°] cohesion [MPa] dilatation angle [°]

joint set 1 α1 = 85° , α2 = 160°

joint set 2 α1 = 85° , α2 = 30°

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

? KEM
Fig. 4.1: Geometry and rock layers used in the KEM model

Tab.4.1: Material properties
material zones Young's modulus [MPa] density [kg/m?] friction angle [°] cohesion [MPa]
AK 1.6 16-17 October 2003, Weimar

granite-gneiss 9000 2500 46 1,2

gneiss 8000 2500 44 1

weak rocks 1000 2500 27 0

quartzite 12000 2500 45 2

disturbed zones 3000 2500 29 0
Numerik in der Geotechnik

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

5. Discussion

→ Results of FEM - calculation

Fig. 5.1: Total displacements contours in equilibrium with gravitational forces
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

Fig. 5.2: Location of the considered three slope intersections

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

1000

800

U total A-A Ux A-A U total B-B Ux B-B U total C-C Ux C-C

K0 = σ`hh / σ`yy
1000 K0 in x A-A K0 in z A-A K0 in x B-B K0 in z B-B K0 in x C-C K0 in z C-C

800

height [m]

400

height [m]

600

600

400

200

200

0 -20

-10

0

10 20 30 40 displacements U [cm]

50

60

70

0

-8

-6

-4

-2

0 K0

2

4

6

8

Fig. 5.3: Total displacements and displacements in x-direction for the three slope intersections

Fig.5.4: K0 factor for the three slope intersections

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

→ Results of KEM – calculation 1 (identical constitutive parameters) factor of safety F=2.42

Fig. 5.5: The geometry of the slip surface obtained with KEM

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

→ Results of KEM – calculation 2 (modified constitutive parameters) cohesion is reduced 75% factor of safety F=1.59

Fig. 5.5: The geometry of the slip surface obtained with KEM

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary

AK 1.6 16-17 October 2003, Weimar

Numerik in der Geotechnik

Analysis of a deep seated slope failure in the Alps
Laboratory of Soil Mechanics

6. Summary
? to evaluate the potential hazard, it is essential to understand the geological situation and mechanisms driving the slope instability ? the analyses base on important assumptions because of missing information ? the finite element analysis was compared with the predictions done using kinematic element method → approximatly same location of the slip line = sliding mass ? improved data – more realistic results can be obtained including time dependency fracturing rock degradation phenomena Next Step: Performing detailed ?Run-out“ analysis with determined failure mass
AK 1.6 16-17 October 2003, Weimar Numerik in der Geotechnik

1. Introduction 2. Geological situation 3. Main assumptions 4. Numerical modelling 5. Discussion 6. Summary


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