Ens 100302 en Fs Tad Lecture 03

8/8/2019 Ens 100302 en Fs Tad Lecture 03

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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

2

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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3

Conventional underground tunnelling

Discontinuous excavation process

Small advance steps

Full face or partial face

EXCAVATING

MUCKING

SUPPORTING


4

Continuous mechanized tunnelling

Continuous excavation

Mucking of excavated material

Support installation

EXCAVATING

MUCKING

SUPPORTING


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5

Drill & Blast


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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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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


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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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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)


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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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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


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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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Charging


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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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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


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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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Mucking

LOAD

TRANSPORT


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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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19

Traditional mechanised tunnelling

Road-header Competent rock

Digger Impact breaker, ripper, pick, and bucketfor weak weathered rock and firm soilBoom Excavator


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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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Conventional Excavators

Weak rocks

Rippers (hard rock inclusions)

Space (rotation and arm

movements)

Foundation stability

No vibrations and fumes


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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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Road-header

Rotating drum

perpendicular to the boom

Rotating drum

in line with the boom


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Muck conveyor


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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



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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


Loose sandysoil

Shield TBM

Gripper TBM

ReamingMachine

Non-Shield TBM

Competent rock

Competent rock

Firm soil


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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Big circular section:

11 m for rock TBM

15 m for shield

Excavating


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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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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



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Tunnel Reaming & Enlarge Machines

Gripper (Tractor)

Axial pilot tunnel

Cutter head

Rear support


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Uetliberg Tunnel (Switzerland)

5 m pilot tunnel

14.4 m final section

Tunnel Bore Extender


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Competent and hard rock formation - Homogeneity

Grippers assure the face advancing

Gripper

Gripper TBM


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Cutting tools


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Single gripper TBM

Double gripper TBM

Gripper TBM


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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



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Gotthard Basis Tunnel (Amsteg)


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Mechanical Face Support


Open Face

Compressed Air Shield


Shield TBM

Gripper TBM

Reaming Machine

Non-Shield TBMRock TBM

Soil TBM

Double Shield


Hybrid Shield



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Open Face Platform Shield


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Open Face Shield - TBM

Open Face Tunnelling Shield Open Face Shield


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TBM with Mechanical Face Support

Flood doors closed

Flood doors open


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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


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Compressed A ir Shield


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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


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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)




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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


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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)




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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


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Double Shield

Gripper + Shield

varying rock formations


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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


Double Shield


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Slurry ModeEPB Mode

EPB + Slurry

varying soil conditions


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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


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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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Applicability

~ ~ ~ ~ Drainage

~ ~ ~ Face

stabilisation

(VTR bolting)

~ ~ ~ Freezing

~ ~ ~ ~ ~Injections

~ Jetting

~ ~Forepoling

~ ~ ~Lances

BlocksLooseground

(without cohesion)

DeformableCohesiveUnstable

CohesiveStableUnstableStable

Ground massRock mass

Ground conditionsMethod


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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)


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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.


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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


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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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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


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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

Documents

Ens 100302 en Fs Tad Lecture 03