tunnel geology

1. Tunnels
Prepared By:-Asim
Nabeel
Hassad
Omer
Ali

2. • WHAT IS TUNNEL?
• It is an underground or underwater passageway, dug
through the surrounding soil/earth/rock.
• They could be used for carrying freights and
passengers, water, sewage, etc.
• A tunnel may be for foot or vehicular road traffic, for
rail traffic, or for a canal.
• Secret tunnels are built for military purposes.
• Special tunnels, such as wildlife crossings, are built to
allow wildlife to cross human- made barriers safely.
• The methods involved are underground operations
known as tunnel driving and the surface is not
disturbed.

3. • REASONS TO BUILD A TUNNEL
• When the lane encounters an obstacle such as a mountain to
avoid bypassing the obstacle.
• Built sometimes to overcome a water obstacle as a
replacement for building a bridge above it.
• Built to connect between military posts so the movement
between them will not be visible for the enemy.
• Sometimes built for infrastructure like electricity cables, water,
communication and sewerage to avoid damage and disruption
above ground.

4. • HISTORY
• the first tunneling was done by prehistoric people
seeking to enlarge their caves.
• First tunnel in Babylonia was a brick-lined pedestrian
passage some 3,000 feet (900 meters) long was built
about 2180 to 2160 B.C. under the Euphrates River to
connect the royal palace with the temple.
• The largest tunnel in ancient times was a 4,800-foot-
long, 25-foot-wide, 30-foot-high road tunnel (the
Pausilippo) between Naples and Pozzuoli, executed in
36 B.C.
• In 1681 gunpowder was first used for blasting the
tunnels. First time the ventilation system for tunnel
was developed in 1927 in Holland tunnel.

5. • In 1952 James . S. Robbins comes up with a good
idea and designs the modern tunnel- boring machine.
• In 1988 Japan's 33-mile-long Seikan Tunnel, the
world's longest and deepest railway tunnel (787 feet
below sea level), connects the islands of Honshu and
Hokkaido.
• In 1994 after 192 years of planning and six years of
building, the Channel Tunnel runs under the English
Channel.

6. TUNNELING METHODS
• depends on
• ground conditions,
• the ground water conditions,
• the length and diameter of the tunnel drive,
• the depth of the tunnel,
• the logistics of supporting the tunnel excavation,
• the final use and shape of the tunnel and appropriate
risk.

7. • ADVANTAGES OF TUNNELING
• Tunnels are more economical than open cuts beyond
certain depths
• Tunnels avoid disturbing or interfering with surface life
and traffic during construction
• Tunnels prove to be cheaper than bridges or open
cuts to carry public utility services like water, sewer
and gas
• if tunnels are provided with easy gradients, the cost of
hauling is decreased
• In case of aerial warfare and bombing of cities, the
tunnels would grant better protection as compared to
bridges.

8. • Parts of Tunnel

9. TUNNEL LININGS
These are the permanent or temporary support for
keeping tunnel from collapse and provide safe.
• Tunnel linings are grouped into three main forms
some or all of which may be used in the construction
of a tunnel:
• 1. Temporary ground support
• 2. Primary lining
• 3. Secondary lining

13. 4. WIRE MESH:-
• Wire mesh is used to support small pieces of loose
rock or as reinforcement for shot crete.
• Two types of wire mesh are commonly used in
underground excavations:
• 1. Chain-link mesh:- commonly used for fencing
• 2. Weld mesh:- commonly used for reinforcing
shotcrete.

14. 5. IN SITU CONCRETING
• The process of placing concrete in situ was
incompatible with timber supports.
• The first uses of concrete were for tunnels in good
rock and it was only with the introduction of steel
supports that concrete became the norm for a tunnel
lining material.
• In-situ forms used for lining tunnels are, with few
exceptions, of the travelling type, constructed of steel.

15. • VENTILATION IN TUNNELS
• Ventilation is required because of
• 1) Dust and gas caused by drilling, blasting, loading of
excavated materials and Shot creting
• 2) Exhaust gas and smoke discharged by diesel
• 3) Poison gas made from explosive or organic solvent
• 4) Poison gas, flammable gas or oxygen shortage gas
in ground
• 5) High temperature and high humidity

16. VENTILATION DURING CONSTRUCTION
• During construction it is necessary to ventilate
a tunnel for various reasons:
• To furnish fresh air for the workers
• To remove the dust caused by drilling, blasting,
mucking, diesel engines, and other operations
• To remove obnoxious gases and fumes
produced by explosives

17. • SHAPES OF TUNNELS
• (A) CIRCULAR :This type of section offers
greater resistance to external pressure .
• If ground is highly unstable , such as soft clay
or sand , it is necessary to use circular section .
• For carrying water and sewerage circulation
shape tunnels are used .ex. Aqueduct
• Circular tunnel are not prefer as traffic tunnel.

19. • ELIPTICAL SECTION
• They are used in grounds compare than rock .
• These tunnels serve as water sewage
condition.
• They are difficult construct .
• They cannot be used as traffic tunnels because
of their narrow base.

21. • EGG – SHAPED SECTION
• These section have narrow cross sections at
bottom. They are best suited for carrying
sewage. They maintain self-cleansing velocity
of flow of sewage both in dry and rainy seasons
.
• They are resist external as well as internal
pressure due to their circular walls .
• These tunnels are difficult to construct

23. • HORSE SHOIE SECTION
• This form consists of a semi-circular roof
together with arched sides and a curved invert.
• They are most popular as traffic tunnels for
road and railway routes .
• These tunnels are also difficult to construct.

25. • TUNNELLING METHODS
• 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

27. • 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 diaphram walls, pin
piles, and decking. Step two :Excavation within
the diaphragm walls, installing structures 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.

29. • TBM (Tunnel Boring Machine)
• tunnel boring machine (TBM) is a machine
used to excavate tunnels with a circular cross
section through a variety of soil and rock strata.
They can bore through anything from hard rock
to sand. Tunnel diameters can range from a
meter to 19.25metre.
• 1. Mechanical-support TBM
• 2. Compressed-air TBM
• 3. Slurry shield TBM
• 4. Earth pressure balance machine.

32. • 1- Mechanical Support TBM
• A mechanical-support TBM has a full-face
cutter head which provides face support by
constantly pushing the excavated material
ahead of the cutter head against the
surrounding ground.
• 2- Compressed-Air TBM
• A compressed-air TBM can have either a full-
face cutter head or excavating arms.
Confinement is achieved by pressurizing the air
in the cutter chamber.

36. • Geological Survey For Tunneling
• A geological survey is the systematic investigation of
the subsurface and surface of a given piece of ground
for the purpose of creating a geological map ,model
and feasibility studies.
• A geological survey employs techniques from the
traditional walk-over survey, studying outcrops and
landforms, to intrusive methods, such as hand
auguring and machine driven boreholes, use of
geophysical techniques and remote sensing methods,
such as aerial photography and satellite imagery etc.

37. • Types Of Geological Survey
• Mainly geological surveys are classified into two types:
• Surface Geological Survey
• Subsurface Geological Survey
• Surface Geological Survey:
• includes on land geology and geological structures,
landforms, hydrology, outcrop pattern ,engineering
properties etc
• Subsurface Geological Survey:
• includes on underground geology and geological
structures, Geo-hydrogeology, subsurface rock or soil
pattern etc.

38. • Surface Geological Survey
• Geological profile is prepared along line of
tunnel.
• Geological observations are done along this
profile like engineering properties of rock/soil,
geological structures like fold, faults, joints,
spring, stream, river alignment and any
seepage etc
• Trial boring plan is prepared along the tunnel
line.

42. • Subsurface Geological Survey
• Trial boring is done along the tunnel line.
• Different rock and soil samples are collected from
subsurface and their physical and chemical properties
are observed.
• Some samples are sent to laboratory for determination
of engineering properties like shearing, strenght,
permeability, porosity, compressive strenght , and
other test are performed.
• GWT(Ground Water Table) is noted and water bearing
strata is marked in geological profile.

43. • Different geophysical surveys like refraction,
resistivity, GPR(Ground Penetrating Radar) and
bore hole logging etc are also done.
• In situ testing like Packer-testing, hydro
fracturing, load-testing etc are performed.
• A geological/feasibility report comprising all
information ,photographs, profile and others
necessary data are presented for final tunnel
design and construction.