This document discusses large tunnel boring machine (TBM) projects in Switzerland, including lessons learned and remaining risks. It describes experiences from recent TBM projects like the Vereina Tunnel and Gotthard Base Tunnel, where crown failures occurred due to weak rock zones. It also discusses a risk-based design approach and uncertainties in predicting TBM penetration rates. The case study of the Lago Bianco Hydropower project demonstrated how different ground conditions and risks were evaluated and addressed through the tunnelling design and construction methods. In conclusion, the document states that remaining TBM tunnelling risks relate to incorrectly predicting system behavior and penetration rates, and that designs should plan for reasonable "worst cases".

1. FJELLSPRENGNINGSDAGEN,
BERGMEKANIKKDAGEN, GEOTEKNIKKDAGEN
2012
LARGE TBM PROJECTS IN
SWITZERLAND –
EXPERIENCE AND STATE OF THE ART
Part 2
Johannes Gollegger & Helmut Wannenmacher
Amberg Engineering Ltd., Switzerland

2. Content
2
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
1. Introduction
3. Risk-based geotechnical design
4. Case study Lago Bianco Hydropower
6. Remaining risks of TBM tunnelling
2. Lessons learned from recent projects
5. Uncertainties in the prediction of penetration rates

3. Introduction
3
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
 Switzerland 40 years of experience
 Development of TBM
 Improved well established technique
 Lessons learned
 Remaining risks

4. Content
4
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
1. Introduction
3. Risk-based geotechnical design
4. Case study Lago Bianco Hydropower
6. Remaining risks of TBM tunnelling
2. Lessons learned from recent projects
5. Uncertainties in the prediction of penetration rates
2.1 Vereina Tunnel
2.2 Gotthard Base Tunnel

5. Vereina Railway Line
5
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Geology of the Vereina Tunnel
 Crystalline rock mass, gneisses and amphibolites
 Foliation is flatly bedded, fissures show narrow spacing

6. Experience Gained at the Vereina Tunnel
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Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Crown failure some sections excavated by TBM
1st causal factor
 Existing geology, flatly bedded foliation
2nd causal factor
 Thrust force, bracing of TBM against the tunnel wall
→Gripper force can lead to opening of existing fissures
→Opening of fissures in existing geology led to crown failure

7. Experience Gained at the Vereina Tunnel
7
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
→Increased supporting measures
→Drop down of advance rate
Excavation rates

8. Content
8
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
1. Introduction
3. Risk-based geotechnical design
4. Case study Lago Bianco Hydropower
6. Remaining risks of TBM tunnelling
2. Lessons learned from recent projects
5. Uncertainties in the prediction of penetration rates
2.1 Vereina Tunnel
2.2 Gotthard Base Tunnel

9. Experience Gained at the Faido Single-Track Tubes
9
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Damages at Following Excavation of West Tube
Invert heaves behind
cutter head including
heave of invert concrete
Contact between
back-up constructions
and rock support

10. Experience Gained at the Faido Single-Track Tubes
10
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Stress redistribution process
Development of
arch
subhorizontal
rock foliation
Primary stress
EST-
East
EST-
West
Stress redistribution due
to excavation of West tube
Deformations
of invert and
crown
Stress redistribution due
to excavation East tube

11. 11
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Radial deformation [cm]
0 5 10 15 20 25 30
0.5
0
1
1.5
2
3
2.5
Pressure[MPa]
Ground reaction curve after
excavation of the first tube
Ground reaction curve after
excavation of the second tube
Flexible lining
Stiff lining
Failure of rock support
Residual resistance
Failure of rock support
Required rock support
Required rock support
Experience Gained at the Faido Single-Track Tubes
Ground reaction curve

12. Experience Gained at the Faido Single-Track Tubes
12
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Encountered geological conditions

13. Experience Gained at the Faido Single-Track Tubes
13
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Crown collapse West tube, blocking of TBM,
first countermeasures
 6 m long weak zone of kakiritic and cataclastic material
> TBM was blocked
 Installation of 4 pipe umbrellas
 Filling of space above cutter head with concrete
 Countermeasures failed

14. Experience Gained at the Faido Single-Track Tubes
14
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Crown collapse West tube, blocking of TBM,
additional countermeasures
 Gel grouting above TBM in order to protect cutter head
from cement grouting
 Cement grouting in order to stabilize collapsed zone
 Adit from east tube
> TBM freed after
20 weeks

15. Experience Gained at the Faido Single-Track Tubes
15
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Lessons learned
 Largest possible overcut
 Robust shield and cutter head
 Shield with variable diameter
 Shortest possible shield
 Sufficiently large thrust force
 The capability of installing flexible support
 The capability of installing support simultaneously with tunnel
driving

16. Content
16
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
1. Introduction
3. Risk-based geotechnical design
4. Case study Lago Bianco Hydropower
6. Remaining risks of TBM tunnelling
2. Lessons learned from recent projects
5. Uncertainties in the prediction of penetration rates

17. Risk Based Geotechnical Design
17
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
TBM
excavation
resonable
Conventional
excavation
Evaluation of excavation
method
Definition of rock mass behaviour
Relevant geotechnical parameters
Primary stress
conditions
Size, shape, location of structure
Orientation of
ground structure
Ground water
Definition of ground types
no
yes

18. Risk Based Geotechnical Design
18
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Risks
acceptable
Evaluation of remaining
risks
Choice of TBM concept including
rock support
Behaviour at
shield
Behaviour fulfils the requirements
Behaviour at
back-up
Behaviour at
cutter head
Definition of system behaviour
no
yes
no
yes

19. Content
19
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
1. Introduction
3. Risk-based geotechnical design
4. Case study Lago Bianco Hydropower
6. Remaining risks of TBM tunnelling
2. Lessons learned from recent projects
5. Uncertainties in the prediction of penetration rates

20. 20
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Lago Bianco Hydropower
Geological, longitudinal profile
2000
3000
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
16000
17000
18000
19000
20000
21000
Lago Bianco
1000
Lago di Poschiavo
2000
3000
Stretta and Bernina
crystalline with Alv zone
Bernina
thrust zone
Musella
granite
Margna
nappe
Malenco
nappe
Margna
nappe
Marinelli
formation
Sella
nappe
Sella
nappe
Musella
granite
© Bild Repower
Source: www.repower.com

21. Experience gained at the Lago Bianco Hydropower
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Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Homogeneous zone A, chainage 1+090 to 6+820
 Massive to blocky gneisses and shists
 Overburden up to 850 m
 Stable rock mass behaviour
 Potential of gravitational overbreaks
 Inhomogeneous face conditions → higher wear rates

22. Experience gained at the Lago Bianco Hydropower
22
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Homogeneous zone A, chainage 1+090 to 6+820
 Massive to blocky gneisses and shists
 Overburden up to 850 m
 Stable rock mass behaviour
 Potential of gravitational overbreaks
 Inhomogeneous face conditions → higher wear rates

23. Experience gained at the Lago Bianco Hydropower
23
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Homogeneous zone B, chainage 6+820 to 7+020
 Overburden approx. 950 m , large deformations, shear failure in crown
 Risk of jamming of TBM
 Shield lubrication, shifting of gauge cutters, grouting
 Local water ingress und limited flowing ground conditions
 Measures: Segmental lining, pipe umbrella, drainage borehole
 Risk acceptable

24. Experience gained at the Lago Bianco Hydropower
24
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Homogeneous zone B, chainage 6+820 to 7+020
 Overburden approx. 950 m , large deformations, shear failure in crown
 Risk of jamming of TBM
 Shield lubrication, shifting of gauge cutters, grouting
 Local water ingress und limited flowing ground conditions
 Measures: Segmental lining, pipe umbrella, drainage borehole
 Risk acceptable

25. Experience gained at the Lago Bianco Hydropower
25
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Homogeneous zone C, chainage 14+760 to 16+050
 Non-cohesive fault zone, stress induced shear- failure
 Major water inflow (up to 210l/s) > risk of flowing ground conditions
 High load on TBM shield and on segments > high risk of jamming
 Risk not acceptable

26. Experience gained at the Lago Bianco Hydropower
26
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Homogeneous zone C, chainage 14+760 to 16+050
 Non-cohesive fault zone, stress induced shear failure
 Major water inflow (up to 210l/s) > risk of flowing ground conditions
 High load on TBM shield and on segments > high risk of jamming
 Risk not acceptable

27. Experience gained at the Lago Bianco Hydropower
27
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Tunnelling concept
 Double shield TBM
 Trapezoidal segments
 Pea gravel and grouting of annular gap
 Flat cutter head
 Anti-wear plates and wedges
 Equipment for exploration drilling
 Umbrella pipe
 Lubrication of shield
 Pumping devices of up to 250 l/s,
 Possibility of probe drillings
 Segments with higher reinforcement and load capacity, with
drainage tubes

28. Content
28
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
1. Introduction
3. Risk-based geotechnical design
4. Case study Lago Bianco Hydropower
6. Remaining risks of TBM tunnelling
2. Lessons learned from recent projects
5. Uncertainties in the prediction of penetration rates

29. Uncertainties in the Prediction of Penetration Rates
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Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Geological and geotechnical influencing factors for penetration
prediction models

30. Uncertainties in the Prediction of Penetration Rates
30
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Influences on penetration rate
 Clogging of mucking buckets (left)
 Cutter failure due to dynamic loads (right)

31. Uncertainties in the Prediction of Penetration Rates
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Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Influences on penetration rate
 Unaxial compressive strength
 Normally oriented angle of fabric towards tunnel axis > maximum penetration
 Parallel oriented angle > minimum penetration
 Stress conditions at the tunnel face
 Failure mode

32. Content
32
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
1. Introduction
3. Risk-based geotechnical design
4. Case study Lago Bianco Hydropower
6. Remaining risks of TBM tunnelling
2. Lessons learned from recent projects
5. Uncertainties in the prediction of penetration rates

33. Risk Based Geotechnical Design
33
Fjellsprengningsdagen, Bergmekanikkdagen, Geoteknikkdagen Oslo, November 22 -23, 2012
Remaining uncertainties of TBM tunnelling are related
 To false prediction of system behaviour
>> Ground investigation with a risk based geotechnical
design
>> Action plan with countermeasures
 To false prediction of penetration rate
>> Reliable failure modes for the determination of
the advance rate
A design for the “Worst Case” is certainly technically
desirable, but cannot always be implemented with
economically justifiable means!!!

34. Thank You Very Much
For Your Attention!