Excavation of Tunnels

EXCAVATION OF

Author: Partha Das sharma, (B.Tech – Hons., in Mining Engineering)
E.mail: sharmapd1@gmail.com, Website: http://miningandblasting.wordpress.com/

TERMINOLOGY for UNDERGROUND
STRUCTURES

Adit
Tunnel
Subway
Shaft
Chamber
Portal
Pilot adit
Centre
Face
Wall ~ site
Floor
Roof

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Overbreak
Excavated profile
Natural archling
Load
Support
Failure
Gentle failure
Rock burst
Squeezing ground
Swelling ground
Clay-filled joint
Long term stability
Ground treatment
Support before excavation


Jet grouted roof cover
Shotcrete initial lining
Jet grouted floor cover
Top heading
Invert
Bench
Final concrete lining
SHIELD tunnelling method
CUT & COVER tunnelling method
TBM (Full face ~ Total Boring Machine)

TERMINOLOGY for EXCAVATIONS of
ROCKS & SOILS
DRILLING
Hardness
Toughness
Abrasiveness
Structure
Drilkling fluids
AUGERING
MACHINE BORING
Total Boring Machine (TBM)
Full face excavation
BLASTING

SCRAPING
RIPPING
DIGGING
GROUND WATER
Control of groundwater
Groundwater flow
Rate of flow
Volume of flow
Boundaries


TUNNEL DESCRIPTION

1. Made into natural material (rocks)
2. Empty inside
3. Carry the loads itself
4. Both ends are open to atmosphere
5. Generally horizontal
6. Thick walled structure looks like cylinder


1- Key stone
2- Arch
3- Wall
4- Floor
5- Bench
6- Bench line or plane
7- Top heading
8- Invert


Tunnel Section for Swelling Ground

1- Digging section
2- Support
3- Swelling section
4- Pressurized area
5- Flow direction of water


SURFACE EXCAVATIONS

Deformation & failure


UNDERGROUND EXCAVATIONS
In Rock
In Sediment
Stability & Arching
Water
Dry tunnel...............above water table
Wet tunnel..............below water table
Gases
Carbon dioxide (CO2)
Carbon monoxide (CO)
Methane (CH4)
Hydrogen sulphide (H2S)
Other gases


Gas bursts
Rock falls
Rock bursts
Squeezing ground
Temperature
Subsidence


EXPLORATION & INVESTIGATIONS
RELATED of SLOPE STABILITY

Geomorphologic maping and preparation of
longitudinal & cross sections
Geological maping & surveyings (aerial
photographs)
Geophysical surveyings
Underground explorations, boreholes
Ground water surveyings
Laboratory tests
Model studies

SURFACE EXCAVATIONS

Permanent
Short term excavations


SUBSURFACE EXCAVATIONS

1. GEOLOGY
a. Soil profile or hard rock geology
b. Structure
c. Ground water (hydrogeology)
d. Stability


2. INVESTIGATIONS
a. Mapping (Topographic, geologic, etc...)
b. Geophysical surveying (especially seismic
velocity of rocks)
c. Trial pits & boreholes
d. General and local stability analysis
e. Decide to excavation method


UNDERGROUND EXCAVATIONS

Adit, shaft, incline, large chamber
Tunnel
Subway ~ metro
Underpass
Shelter
Power house
Ware house, store, mining ...etc


GASES
(can be lethal or burst)

Carbon monoxide (CO) 0.97 of air
Carbon dioxide (CO2) 1.53 of air
Methane (CH4) 0.55 of air
(Highly explosive with air) marsh gas

Hydrogene sulphide (H2S) 1.19 of air
(Highly toxic and explosive)
Sulphur dioxide (SO2)


ROCK FALL

SQUEEZING GROUND (sand, silt, shale, clay)

ROCK BURST

BULKING (Increase in volume, 10-40%)


FACTORS EFFECTING
EXCAVATION of ROCKS

Mineralogical composition of rocks
Texture & fabric
Petrographic features
Structure
Rock mass
Strike & dip of beds in relation to face of
excavation
Intensity of tectonic disturbances
Degreee of weathering

RESISTANCE of ROCKS to EXCAVATION

Loose soils
Soil easy to spade
Soil easy to dig
Crumbling weak rocks
Rocks easy to blast
Rocks difficult to blast
Rocks very difficult to blast


SHIELD TUNNELLING METHOD

This method involves the use of shield machine to
drive the tunnels below the ground.
After completion of a work shaft, the shield machine
is lowered into the shaft and assembled there before
excavation and construction of the tunnels using
precast concrete lining segments of about 1.2 meter
width.
This construction method causes minimal disruption
to traffic and the environment because all the work
takes place below ground and the ground level
environment is unaffected.


CUT and COVER TUNNELLING METHOD

This construction method, whereby the site is fully
excavated, the structure built and then covered over,
uses diaphragm walls as temporary retaining walls
within the site area.
Step one :Construction of diaphragm walls, pin piles,
and decking.
Step two :Excavation within the diaphragm walls,
installing struts as work progresses.
Step three :Construction of permanent floor slabs and
walls.
Step four : Fitting out the internal structures,
backfilling, and reinstating the surface structures.


TBM (Tunnel Boring Machine)

1. Mechanical-support TBM
2. Compressed-air TBM
3. Slurry shield TBM
4. Earth pressure balance machine
5. Mixed-face shield TBM


1- Mechanical Support TBM

A mechanical-support TBM has a full-face
cutterhead which provides face support by
constantly pushing the excavated material
ahead of the cutterhead against the
surrounding ground.


2- Compressed-Air TBM

A compressed-air TBM can have either a full-
face cutterhead or excavating arms.
Confinement is achieved by pressurizing the
air in the cutter chamber.


3- Slurry Shield TBM

A slurry shield TBM has a full-face
cutterhead. Confinement is achieved by
pressurizing boring fluid inside the cutterhead
chamber.


4- Earth Pressure Balance Machine

An earth pressure balance machine has a
full-face cutterhead. Confinement is achieved
by pressurizing the excavated material in the
cutterhead chamber.


5- Mix-Face Shield TBM

Mix-face shield TBMs have full-face
cutterheads and can work inclosed or open
mode and with different confinement
techniques.


EFFECT of GEOLOGICAL STRUCTURES
to TUNNEL EXCAVATION
Effect of soil layers: horizontal, vertical and
inclined layers have different kinds of loading
conditions for tunnels.


Effect of faults: the relation between the fault
slope direction and the tunnel direction, width of
the fault zone, type and thickness of the fill
material and the hydrostatic pressures in both
sides of the fault are some problems in the
tunnelling.

Relation between the fault zone and the tunnel


Tunnel excavations in the slopes: the
discontinuities (layers, fissures) inclined inside or
outside of the slope are very important regarding the
stress and strength of the tunnel.


Effect of the folds: While tunnel is excavated in an
area that contains folded rocks, different stresses and
conditions may occur depending on the fold type.

Fold axis and the tunnel direction is parallel
Fold axis and the tunnel direction is vertical


CLASSIFICATION of ROCKS for
TUNNELING PURPOSES

Classification of rocks for engineering
purposes is needed in analyzing the project
costs and to obtain an economic and reliable
solution.

The classification of the rocks, that the tunnel
will be constructed in, is first done by
Terzaghi. But, it is too general and gives
qualitative results.

Rock classification and determination of unsupported span


ONE of the LONGEST IRRIGATION TUNNELS in
the WORLD


Consist of two concrete lined tunnels
each of which is 7.62 m in diameter and
26.4 km in length discharging water from
the reservoir of Atatürk Dam.


Excavation of Tunnels

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