By Shri Manoj Verman, President, Indian National Group of ISRM President, International Commission on Hard Rock Excavation Vice President, Indian Society of Engineering Geology at 31st National Convention of Civil Engineering organised by Gujarat State Center, The Institution of Engineers (India) at Ahmedabad

1. Dr Manoj Verman
Tunnelling & Rock Engineering Consultant
CHALLENGES OF TUNNELLING
A PEEP INTO THE EXCITING WORLD OF TUNNELLING
CHALLENGES OF TUNNELLING
A PEEP INTO THE EXCITING WORLD OF TUNNELLING

2. CHALLENGES OF TUNNELLING
A PEEP INTO THE EXCITING WORLD OF TUNNELLING
Dr Manoj Verman
President, Indian National Group of ISRM
President, International Commission on Hard Rock Excavation
Vice President, Indian Society of Engineering Geology

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LET THE JOURNEY BEGIN…………………….
www.sammode.com

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SARDAR SAROVAR PROJECT, GUJARAT
AvtarKaul(panoramio.com)
GettyImages
Access tunnel to underground powerhouse Underground powerhouse

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THE HIMALAYAS, THE ANDES & THE ALPS – THE MOST
DIFFICULT TUNNELLING MEDIA IN THE WORLD
Himalayas
Alps
Andes

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TUNNEL BEHAVIOUR
• Tunnel behaviour is influenced by:
Insitu and induced stress
Geological structure/jointing,
 Rock mass strength, and
Groundwater conditions.

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Different behaviours,
different design solutions

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Increasing Structural
Instability Due to
Lack of Confining
Stress

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STRUCTURALLY CONTROLLED CONDITION
• Structurally controlled failure in strong rock
– gravity driven blocks can be controlled by
rock bolting

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STRUCTURALLY CONTROLLED CONDITION
• Failure of a wedge in the roof of a
12m span tailrace tunnel for the
Rio Grande project in Argentina

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CAVING IN A TUNNEL IN J&K

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IncreasingSpallingwith
HigherStressLevel

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BRITTLE CONDITION
• Highly stressed massive rock –Spalling and
slabbing can be controlled by combinations of
rockbolts and mesh

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ROCK BURST IN GOTTHARD BASE TUNNEL,
SWITZERLAND (STRESS DRIVEN FAILURE)

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ROCK BURST AT TUNNEL FACE (STRESS DRIVEN
FAILURE)

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BRITTLE CONDITION
Maximum boundary
stress / Uniaxial
Compressive strength
Spalling
description
smax/sc ≈ 0.9 Minor to
moderate
spalling
smax/sc ≈ 1.2 Severe spalling
occurs
smax/sc ≈ 1.6 Spalling takes the
form of
rockbursts in
hard brittle rock

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IncreasingSqueezing
ProblemwithIncreasing
StressLevel

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SQUEEZING CONDITION
• Squeezing conditions in weak rock
masses – failure zone around a tunnel
generally requires the installation of
passive support (i.e. concrete lining)

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SQUEEZING IN ST MARTIN LA PORTE ADIT TO TURIN-
LYON TUNNEL

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SQUEEZING IN HEAD RACE TUNNEL OF
CHAMELIYA HYDROPOWER PROJECT, NEPAL

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SQUEEZING IN HEAD RACE TUNNEL OF
CHAMELIYA HYDROPOWER PROJECT, NEPAL

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SQUEEZING CONDITION
Yacambu-Quibor
water transfer
tunnel, Venezuela
Nathpa Jhakri
headrace tunnel,
India
Mucha highway
tunnel, Taiwan
Old mine
tunnel,
Africa
Driskos highway
tunnel, Greece
Plot from Hoek and Marinos (2000)

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TUNNEL INSTABILITY MODES
Tunnel
Condition
Analysis Methods
Stress analysis (RocSupport, Phase2, RS3)
• Rock support interaction analysis
• Installation sequence
• Tunnel strain evaluation
• Stereonet methods for joint projections (DIPS)
• Wedge analysis (Unwedge)
Stress analysis to determine depth of failure (Phase2, RS3)
Stress analysis that can predict complex instability modes
(Phase2, RS3)

28. TYPICAL CHALLENGES
(A) COVER – UP TO 2000M (>50MPA CONFINING STRESSES)

29. MAINTAINING ACCESS
Avalanches, bad
roads, landslides,
rockfalls, supply
problems, payment
problems etc

30. WATER UNDER PRESSURE
Often also hot – 50-60°C

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INGRESS OF SILT LADEN WATER AT TUNNEL FACE

32. ROCK TEMPERATURE

33. Faults & rock strength
& … the two ends of the rock competence scale
Weak Ground –
Squeezing
Competent Ground – Bursting
Graphite Schist
Quartzite

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FAULTS
• Faults are fractures in crustal strata along
which rocks have been displaced
• The amount of displacement may vary
from only a few tens of millimetres to
several hundred kilometres
• In many faults, the fracture is a clean
break; in others, the displacement is not
restricted to a simple fracture, but is
developed throughout a fault zone
Fault in strata of the Limestone Group, Lower
Carboniferous, near Howick, Northumberland, England

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KALIASAUR – THE FAMOUS LANDSLIDE
(ON ROAD FROM SRINAGAR TO RUDRAPRAYAG, UTTARAKHAND
Kaliasaur - Crushed and broken quartzite rock mass associated with the ENE-WSW sub-
vertical fault system. Rock mass appears tectonically disturbed and completely broken.

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KALIASAUR – THE FAMOUS LANDSLIDE

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FAULTS
Completely crushed
material in a fault zone
near Devprayag,
Uttarakhand

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HIMALAYAN FAULT ZONES
• In general, the fault zones consist of
a highly deformed fault core (core
zone) and of a surrounding and
very fractured “damage zone”
• In these fault zones, water
circulation can also trigger
weathering processes due highly
fractured rocks, generating gouge
material (clayey sub-products)
• The expected thickness of the core
zone generally varies from 1 to
10m.

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“TOOTHPASTE” FAULT
(MYLONITIZED & GRANULATED
 Mud flow Conditions
 50m back from face
100 m mudflow along
tunnel
Severe Disruption to
already installed
support
Conditions much easier
WITHOUT WATER

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GRAPHITIC SCHIST FAULT ZONE
> 9 MONTHS DELAY ~ SEVERE WATER

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UMBRELLA FOREPOLING IN PROGRESS THROUGH 1KM
WIDE DAJ KHAD FAULT ZONE (NATHPA-JHAKRI
PROJECT)

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THE HIMALAYAS
COMPLEX FAULTS

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“TOOTHPASTE”
FAULT
(MYLONITIZED &
GRANULATED
GNEISS)
• 100 m mudflow along tunnel
• Severe Disruption to already installed support
• Conditions much easier WITHOUT WATER

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CLOSURE IN EXCESS
OF 2M
• Various
Multi-Drift
Methods
proposed
• Some
utilized
One of the
Faults

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FREQUENTLY CHANGING GEOLOGY AND OTHER
CONDITIONS – SECTORISE THE TUNNEL
September 27, 2015 46

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Wedge instability  Rockfall
Support class A  B  C1
Main design action Mitigations
Confinement of rock wedges Bolts and fibre-reinforced shotcrete
Control of water pressure/inflow Drainages in advance
Long term stability Concrete final lining
Examples of Support Types

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Rockfall/caving  Severe caving (faults,..)
Support class C2  F
Main design action Mitigations
Increase self-supporting
capacity
Forepoling  umbrella pipes
Stabilisation of tunnel face (F) Pre-consolidation by fibreglass elements
Control of water
pressure/inflow
Drainages in advance
Radial reinforce and
confinament
Lattice girders/Steel ribs, fbr shotcrete,
bolts
Long term stability Concrete final lining with invert (F)
Examples of Support Types

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Hazard Wedge instability
Description Gravitational fall of rock blocks isolated by the
discontinuity network (weight force>shear
strength)
Instability Generally sudden, short term instability
Evolution Frequently an equilibrium condition is reached,
but this may be after fall of other wedges
Mitigation Preventive bolting, reduction of round length,..
V-Unstable wedges (2/6)Unstable Wedges

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K2
K1
K3
Unstable Wedges

51. Potential wedge instability from tunnel face
Limit equilibrium analysis
Unstable Wedges

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Technical solution at the
face:
Inclined Swellex MN16
dowels, L=6m
Unstable Wedges

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Hazard Caving
Description Gravitational fall of portions of fractured rock
mass or weakly cohesive soils, eventually
alimented by the presence of water
Instability Generally sudden, short term instability
Evolution The complete collapse of the face may be
reached, with concurrent caving of tunnel crown
contour (chimney formation)
Mitigation Drainages, preconsolidation of the core,
prearmature/preconfinement of contour
excavation..
Caving

54. Caving
A tunnel in USBRL
Project, J&K

55. Technical solution for face
instability:
GALLERIE MO
Titolo :
PROGET
ANA





 ³
d
- Drainages (d)
fb
- cemented fibreglass (fb) u
u
- pipe umbrella arch (u)
Caving

56. Collapse of the face intercepting suddenly unforeseen water bearing, very fractured
and weathered rock mass (H=30m)
Vispa tunnel (Italy)
Caving

57. Technical solution 1 (>silty sands):
Menaggio tunnel (Italy)
VI-Caving (10/15)
- Drainages (d)
d
- Protective canopy:
jg+ pipe umbrella (u)
jg+u
- Jet grouting (jg) at
the face
jg

58. Menaggio tunnel (Italy)
s
Technical solution 2 (>mix
condition):
VI-Caving (11/15)
- Drainages (d)
d
- Protective canopy: jg+
pipe umbrella (u)
jg+u
jg+u
- face reinforcement by
jg/ cemented fibreglass
fb (lower section in
silty clay)
jg/fb

59. VI-Caving
Prevalent clayey - silt
Prevalent silty - sands Jet-grouting
Fibreglass

61. D&B VS.
MACHINES