This document analyzes factors that influence the thrust-penetration gradient of hard rock tunnel boring machines (TBMs), including: - Rock properties like strength, anisotropy, joints, and stress conditions affect the gradient. Low rock strength and high stress result in a high gradient. - Tunnel diameter impacts the gradient, with smaller diameters having a lower gradient. - Overburden affects the gradient, with higher overburden/strength ratios giving a higher and more variable gradient. - Joint alteration from hydrothermal activity can significantly decrease the gradient by strengthening the rock mass, as seen at the Nant de Drance project.

1. Dr. M. Weh
H. Wannenmacher
WTC 2014
Marti Holding AG
www.martiag.ch
Unexpected performance and cost factors for hard rock
TBM. Analyses of specific cases with the thrust- penetration
gradient
• Thrust-Penetration
Gradient
• Influence of Tunnel
diameter
• Influence of
overburden
• Influence of joint
alteration
Thrust-
Penetration
Gradient
Influence of
Tunnel
diameter
Influence of
overburden
Influence of
joint
alteration

2. Dr. M. Weh
H. Wannenmacher
WTC 2014
Marti Holding AG
www.martiag.ch
Unexpected performance and cost factors for hard rock
TBM. Analyses of specific cases with the thrust- penetration
gradient
TBM-specific influencing
factors
• Type, spacing and
wear rate of cutters.
• TBM-diameter.
• Thrust per cutter.
Intact Rock/ Rock Mass
influencing factors:
• Intact UCS.
• Grade and orientation of
anisotropy of rock mass.
• Joint conditions, joint
orientation towards the
tunnel alignment and
spacing of joints.
• Magnitude and orientation
of stress conditions and
effects of stress
redistribution on rock mass
behaviour.
Thrust-
Penetration
Gradient
Influence of
Tunnel
diameter
Influence of
overburden
Influence of
joint
alteration
0
5
10
15
20
25
30
35
40
0 50 100 150 200
penetration(mm/rev)
thrust/cutter (kN)
Islisbergtunnel, Silt/Sandstone: 30MPa
Gorgier, Marlestone: 28MPa
Gorgier, Limestone: 120MPa
Bure: Marlestone: 20MPa
Bure, Limestone: 130MPa
Katzenberg, Limestone: 100MPa
Katzenberg: Marlestone, 10MPa
Low rock strength: High gradient
High rock strength: Low gradient

3. Dr. M. Weh
H. Wannenmacher
WTC 2014
Marti Holding AG
www.martiag.ch
Unexpected performance and cost factors for hard rock
TBM. Analyses of specific cases with the thrust- penetration
gradient
Scale dependency of tunnel radii on the thrust penetration gradient
Small tunnel diameter: Low gradient
Big tunnel diameter: High gradient
Thrust-
Penetration
Gradient
Influence of
Tunnel
diameter
Influence of
overburden
Influence of
joint
alteration
0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150 200 250
thrustpenetrationgradient
(mm/rev/kN/cutter)
uniaxial compressive strength (MPa)
TBM projects with overburden < 1000m
r > 5500mm
3500 < r < 5500mm
2500 < r < 3500mm
r < 2500m
Tunnelradius:
Factor 2 in diameter is more than factor 2 in gradient

4. Dr. M. Weh
H. Wannenmacher
WTC 2014
Marti Holding AG
www.martiag.ch
Unexpected performance and cost factors for hard rock
TBM. Analyses of specific cases with the thrust- penetration
gradient
Influence of stress on the thrust-penetration gradient
Relation overburden/UCS < 4: Low thrust-penetration gradient
Relation overburden/UCS > 7: High thrust-penetration gradient (+60%)
Thrust-
Penetration
Gradient
Influence of
Tunnel
diameter
Influence of
overburden
Influence of
joint
alteration
y = 0.6363x-0.437
R² = 0.9133
y = 1.2921x-0.495
R² = 0.5069
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0 50 100 150 200 250 300
thrustpenetrationgradient
(mm/rev/kN/cutter)
uniaxial compressive strength (MPa)
TBM radius = 4715mm
overburden/UCS < 4,
Löschberg
4 < overburden/UCS < 7;
Lötschberg
overburden/UCS > 7:
Lötschberg

5. Dr. M. Weh
H. Wannenmacher
WTC 2014
Marti Holding AG
www.martiag.ch
Unexpected performance and cost factors for hard rock
TBM. Analyses of specific cases with the thrust- penetration
gradient
Influence of stress on the thrust-penetration gradient
Relation overburden/UCS small: Narrow distribution of gradient
Relation overburden/UCS high: Wide distribution of gradient
Thrust-
Penetration
Gradient
Influence of
Tunnel
diameter
Influence of
overburden
Influence of
joint
alteration
0%
5%
10%
15%
20%
25%
30%
35%
frequency(%)
gradient (mm/rev/kN/cutter)
0%
5%
10%
15%
20%
25%
30%
35%
frequency(%)
gradient (mm/rev/kN/cutter)
0%
5%
10%
15%
20%
25%
30%
35%
frequency(%)
gradient (mm/rev/kN/cutter)
0%
5%
10%
15%
20%
25%
30%
35%
frequency(%)
gradient (mm/rev/kN/cutter)
Fine grained migmatitic gneiss (270MPa,
overburden/UCS = 6.3)
Coarse grained granite (150MPa,
overburden/UCS = 9.8)
migmatitic gneiss (112MPa,
overburden/UCS = 5.55)
metamorphic slates (77MPa,
overburden/UCS = 5.03)
0.005
0.015
0.025
0.035
0.045
0.055
0.065
0.075
0.085
0.095
0.105
0.115
0.125
0.135
0.145
0.155
0.165
0.175
0.005
0.015
0.025
0.035
0.045
0.055
0.065
0.075
0.085
0.095
0.105
0.115
0.125
0.135
0.145
0.155
0.165
0.175
0.005
0.015
0.025
0.035
0.045
0.055
0.065
0.075
0.085
0.095
0.105
0.115
0.125
0.135
0.145
0.155
0.165
0.175
0.005
0.015
0.025
0.035
0.045
0.055
0.065
0.075
0.085
0.095
0.105
0.115
0.125
0.135
0.145
0.155
0.165
0.175
unstable faceunstable face

6. Dr. M. Weh
H. Wannenmacher
WTC 2014
Marti Holding AG
www.martiag.ch
Unexpected performance and cost factors for hard rock
TBM. Analyses of specific cases with the thrust- penetration
gradient
Influence of joint alteration on the thrust-penetration gradient
Thrust-
Penetration
Gradient
Influence of
Tunnel
diameter
Influence of
overburden
Influence of
joint
alteration
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0 2 4 6 8 10 12 14
thrustpenetrationgradient
(mm/rev/kN/cutter)
overburden/UCS
TBM radius = 4715-4725mm
Löschberg
Nant de Drance
Unexpected low gradient expierenced in the
access tunnel of Nant de Drance P.S.S. .

7. Dr. M. Weh
H. Wannenmacher
WTC 2014
Marti Holding AG
www.martiag.ch
Unexpected performance and cost factors for hard rock
TBM. Analyses of specific cases with the thrust- penetration
gradient
Influence of joint alteration (Nant de Drance P.S.S.)
Thrust-
Penetration
Gradient
Influence of
Tunnel
diameter
Influence of
overburden
Influence of
joint
alteration
Healing of joints (growth of chlorite and quartz) due to hydrothermal activity
 increases strength of rock mass
 decreases the thrust-penetration gradient significantly .