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
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
6
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
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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
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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
21. Experience gained at the Lago Bianco Hydropower
21
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
29
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
31
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!!!