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Tunnel Engineering
Design and Analysis
COURSE LECTURES
#03 Tunnel Excavation Methods
Dr Federica Sandrone
EPFLENACLMR
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Outline
1. Drill-and-blast tunnelling in rocks
2. Roadheader and other excavation machines
3. Tunnel boring machine in rocks
4. Shield tunnelling machine in soils
5. Ground improvements during excavation
6. Selection criteria of excavation methods
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Conventional underground tunnelling
Discontinuous excavation process
Small advance steps
Full face or partial face
EXCAVATING
MUCKING
SUPPORTING
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Continuous mechanized tunnelling
Continuous excavation
Mucking of excavated material
Support installation
EXCAVATING
MUCKING
SUPPORTING
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Drill & Blast
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Excavation cycle
Drilling
1-2 h
Charging
1 h
Ventilation
Scaling
1-2 hMucking
1-3 h
Shotcreting
Firing
Bolting
1-2 h
1 h
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Drilling methods
Penetration rate is a function of geological conditions
All kinds of rock
54-102 mm diameter
All kinds of rock
> 152 mm diameter
Tricone
Medium to hard rock /
abrasive rock also
102-203 mm diameter
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Tunnel b lasting
A Cut
B, C Stoping holes
D Contour: Roof & Wall holes
E Floor holes (lifters)
F Second contour
A
B
C
D
E
F
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Roof, wall and floor holes have to be angled out of the contour (LOOK OUT)
to allow space for the drilling equipment for the coming round keeping the
designed area.
LOOK OUT < 10 cm + 3 cm/hole depth
Contour holes: Look-out (L)
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Cut
Tunnel blasting: one free surface
Second free surface has to be created (cut)
The rock can break and be thrown away from the surface
V-cut Fan cut
Parallel cut
Empty
holes60
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Number of holes Rule of a thumb
Diameter: 45 mm
Length: 4 m
Number = section size (m2) + 35
With larger holes the number decreases slightly
With longer rounds the number increases
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Explosive powders Less used
Explosive gelatines Mainly used as booster or for opening the cut slot
ANFO (Ammonium Nitrate Fuel Oil) Cheap and quite
widespread but not water
resistant
Emulsions (slurries) Pumpable, water resistant, widespread
Explosives - Charging
The charging of blastholes can be carried out either manually with plastic
pipe charges or mechanically with pneumatic charging equipment
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Charging
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Firing
The ignition system:
Electric detonators or non-electric detonators (NONEL)
Detonating cords
Retards (reducing vibrations & new free surfaces)
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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After firing: fumes high temperatures & harmful
concentrations of:
Carbon Monoxide CO
Carbon Dioxide CO2
Nitrogen Oxides NOx
Dust
Ventilation is necessary [Recommendation SIA 196, 1998]
Ventilation
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Scaling
Remove potentially unstable blocks
Preparing the rock surface for shotcreting and/or bolting
Dangerous operation for workers
Manual, mechanised
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Mucking
LOAD
TRANSPORT
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Drill & Blast
Requires advancing interruption forventilation and scaling
Suitable to excavate hard rocks
No protection or support given to therock while scaling
Flexibility
Vibrations and fumesPossibility of excavating tunnels ofdifferent sizes and shapes
OverbreakLow capital investment (short tunnels)
DRAWBACKS ADVANTAGES
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Traditional mechanised tunnelling
Road-header Competent rock
Digger Impact breaker, ripper, pick, and bucketfor weak weathered rock and firm soilBoom Excavator
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Digger / Hammer
Flexibility (weak rocks)
Performances comparable with
drill and blast
No vibrations and fumes
Dust (water spraying)
Hydraulic or pneumatic
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Conventional Excavators
Weak rocks
Rippers (hard rock inclusions)
Space (rotation and arm
movements)
Foundation stability
No vibrations and fumes
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Moderate rock strength (up to 120 MPa)Cutter-head
Extension arm or Boom
Muck conveyor
Crawler chassis
Loading apron
Road-header
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Road-header
Rotating drum
perpendicular to the boom
Rotating drum
in line with the boom
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Muck conveyor
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Road headers & Excavators
Space for rotation and movementsRelatively short time from order todelivery at the site
Stable foundationsLow capital investment
No installation time needed
Need to threat dust with sprayedwater
No vibration and fumes
No protection or support given to therock while excavating. Limited tostable ground.
Flexibility
Suitable to excavate rocks of UCS upto 120 MPa
Possibility of excavating tunnels ofdifferent sizes and shapes
DRAWBACKS ADVANTAGES
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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MechanicalFace Support
Earth PressureBalance Shield
Open Face
CompressedAir Shield
Slurry /Hydro-Shield
Weak, soft rock Firm soil
Soft clay
Weathered, highlyfractured rock
Rock-soil mixedground
Firm soil withgroundwater
Rock-soil mixedground
Loose sandysoil
Shield TBM
Gripper TBM
ReamingMachine
Non-Shield TBM
Competent rock
Competent rock
Firm soil
Rock-soil mixedground
Rock TBM
Soil TBM
Double Shield Ground conditions from competent rockto loose/soft soil
EPB-SlurryConvertible Shield
Varying ground conditions suitable forEPB and slurry machines
Hybrid Shield
Tunnel Boring Machines
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Big circular section:
11 m for rock TBM
15 m for shield
Excavating
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Mucking & Supporting
Ring erection: short time
(20-40 minutes per ring)Continuous mucking from the excavation face
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Mechanical Face Support
Earth Pressure Balance Shield
Open Face
Compressed Air Shield
Slurry / Hydro-Shield
Shield TBM
Gripper TBM
Reaming Machine
Non-Shield TBMRock TBM
Soil TBM
Double Shield
EPB-Slurry Convertible Shield
Hybrid Shield
Tunnel Boring Machines
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Tunnel Reaming & Enlarge Machines
Gripper (Tractor)
Axial pilot tunnel
Cutter head
Rear support
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Uetliberg Tunnel (Switzerland)
5 m pilot tunnel
14.4 m final section
Tunnel Bore Extender
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Competent and hard rock formation - Homogeneity
Grippers assure the face advancing
Gripper
Gripper TBM
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Cutting tools
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Single gripper TBM
Double gripper TBM
Gripper TBM
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Gripper TBM
No protection or support given to the
rock while excavating. Limited to
stable rock
Visual contact with the rock mass
Small flexibility (fault zones, not
homogeneous rocks)
Suitable to excavate hard rocks of
UCS up to 300 MPa
Dust treatment is needed
Free space for ground probing
equipment (treatment and
investigation)
Minor ground support measures
(shotcrete, rock bolts) if necessary
can be installed very close to the
excavation face
DRAWBACKS ADVANTAGES
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Gotthard Basis Tunnel (Amsteg)
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Mechanical Face Support
Earth Pressure Balance Shield
Open Face
Compressed Air Shield
Slurry / Hydro-Shield
Shield TBM
Gripper TBM
Reaming Machine
Non-Shield TBMRock TBM
Soil TBM
Double Shield
EPB-Slurry Convertible Shield
Hybrid Shield
Tunnel Boring Machines
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Open Face Platform Shield
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Open Face Shield - TBM
Open Face Tunnelling Shield Open Face Shield
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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TBM with Mechanical Face Support
Flood doors closed
Flood doors open
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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TBM with Mechanical Face Support
It usually does not have a pressure chamber to support the
tunnel face
Excavated materials can be transported directly from the cutter
head
Rock & firm soil
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Compressed A ir Shield
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Compressed A ir Shield
Groundwater-bearing soil
Water penetration can be prevented by:
Shield
Part of the tunnel section is protected by a lock system using
compressed air
Continuous monitoring and automatic adjustment of required
pressure for supporting tunnel face
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Slurry / Hydro-Shield
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Need of large separation plants for
bentonite treatment
Equal distribution of pressures
against mixed-face conditions
Bad performance in clayey-silty
grounds (polymers addition)Good performance in sand and gravel
Access to the face (mud-cake +
compressed air)
DRAWBACKS ADVANTAGES
Slurry / Hydro-Shield
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Earth Pressure Balance Shield
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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EPB Shield
Face supported by
excavated earth
(under pressure inside
the excavation chamber)
Excavation debris is removed from the excavation
chamber by a screw conveyor which allows the
gradual reduction of pressure
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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More difficult access to the face (no
mud-cake)
Irregular distribution of pressure
against mixed face conditions
Very well adapted for silty and clayey
grounds (limited or no self supporting
capacity)
Problems when boulders are
encountered: no rock crusher
No need of separation plant no
bentonite used
Wearing of the screw can lead to bad
pressure distribution
The use of additives (foams) enables
EPBs to be used with sandy gravelysoil (current trend)
DRAWBACKS ADVANTAGES
Earth Pressure Balance Shield
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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0.001 0.002 0.006 0.02 0.06 0.2 0.6 2.0 6.0 20 60
20
10
0
50
60
70
80
90
100
40
30
Percentage
Passing
Particle Size (mm)CoarseFine
GravelSandSiltClay
SOIL
EPB
Hydroshield
Slurry
Particle Size Distribution
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Double Shield
Gripper + Shield
varying rock formations
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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More expensive
Maintenance problems of articulation
between the shieldsBigger flexibility
A bigger shield surface is not
adapted to squeezing groundsHigher advancement rates
Performance improvement for a
single shield is not really doubled
Avoiding segmental lining when not
needed (reduced costs)
Ground treatment and/or probingthrough the gap between shields
DRAWBACKS ADVANTAGES
Double Shield
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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EPB-Slurry Convertible Shield
Slurry ModeEPB Mode
EPB + Slurry
varying soil conditions
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Ground Improvement
When the rock mass is unstable, to ensure the opening stability
Can be a local intervention or a systematic reinforcementIn the first case it represents mainly a temporary solution while
in the second case the ground/rock mass behaviour is
improved and rock/ground changes their characteristics
Tunnel reinforcement should be taken into account when the
support structure is dimensioned and installed
The effectiveness of rock/ground improvements can be
monitored and the solution adapted to advancing conditions
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Ground improvement during excavation
Very low ground cohesion and strength
Unstable excavated length
Pre-driven support:
Lances
Forepoling
VTR face bolting
Consolidation:
Injection
Jetting
Freezing (temporary)
Drainage
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Applicability
~ ~ ~ ~ Drainage
~ ~ ~ Face
stabilisation
(VTR bolting)
~ ~ ~ Freezing
~ ~ ~ ~ ~Injections
~ Jetting
~ ~Forepoling
~ ~ ~Lances
BlocksLooseground
(without cohesion)
DeformableCohesiveUnstable
CohesiveStableUnstableStable
Ground massRock mass
Ground conditionsMethod
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Lances / Marciavanti
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Forepoling
Steel rods ~ 4 m
Prevent large surface
settlements (low
overburden and/or
poor ground)
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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VTR face bolting
Lunardi Method
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Injection
Ground mass cohesion
Cement Grouts: cement content between 100 and 500 kg per m3 & bentonite. Severalhours must be awaited for setting before any blasting and drilling into the groutedarea.
Micro Cements
Colloidal silica suspensions
Chemical Grouts: Sodium silicate. Reduced setting (30-60 minutes).
Polyurethanes: They react with water and produce foam, which remains ductile after
hardening.
Acrylic Grouts: Liquids of low viscosity. Polymerisation setting on around 1 hour.
Epoxy Resins: Less used.
Thermoplastic materials: Asphalt or melt polyamides pumped with fast flowing water.
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Jetting
quality of the ground around the tunnel
Seal the tunnel against groundwater and thus prevent heading inrushes
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Drainage
Collect water inflow and reduce water pressure
face stabilisation become easier
Pumping well
Tunnel
Pumping well
Original groundwater table
Lowered groundwater table
Ground
Tunnel
Original groundwater table
Lowered groundwater table
Ground
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Freezing
Temporary ground improvement to
avoid water inflow and tunnel
collapse.
Circulation of a refrigerated coolant
through a series of subsurface pipes
to convert soil water to ice & create a
strong and watertight material.
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Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Selection criteria of excavation methods (1/2)
Geological conditions:
Rock or soil
Rock strength and abrasiveness
Soil cohesion & grains size distribution
Presence of water
Homogeneity
Tunnel EngineeringDesign and AnalysisLaboratoire de Mcanique des Roches - LMR
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Selection criteria of excavation methods (2/2)
Tunnel depth
Tunnel location (vibration, place)
Tunnel length (costs)
Time (delivery and installation)
Final use