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1. TUNNELS
•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.

2. NEED FOR TUNNELING
•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.

3. •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.

4. ROOF: The rock or soil in the ceiling immediately above the tunnel bore.
SIDES: Opposite walls of tunnel bore all along its length.
FLOOR: Bottom of the tunnel bore on which rails and machineries are laid
and men walk and work.
FACE: The surface exposed by excavation at the end of the tunnel heading
which is further excavated to advanced tunnelling.
PERIMETER: The tunnel bore boundary. (Pay line)
OVERBREAK: Shuttering of rock beyond the pay line, due to blasting.
TERMINOLOGIES IN TUNNELING

5. SUPPORT: Wooden, brick, stone, concrete or steel structure erected in the tunnel bore after blasting to
protect workings and men from rock fall.
LINING: Brick, stone, cast iron or steel casing placed around a tunnel and or grouting to give smooth
surface
SHAFT: Vertical or steeply inclined circular or rectangular well like excavation from the surface, down to
intersect tunnel at depth for finding or verifying geological confirmation, hauling man and material and
ventilating tunnels and other underground structures.

6. SHAPES OF TUNNELS

7. •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
circular shape tunnels are used eg
Aqueduct.
•Circular tunnel are not preferred as
traffic tunnel.
CIRCULAR

8. •These sections 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 resist external as well as internal
pressure due to their circular walls .
•These tunnels are difficult to construct.
EGG - SHAPED
SECTION

9. ELLIPTICAL SECTION
•These are used in water sewage system.
•They are difficult to construct.
•They cannot be used as traffic tunnels
because of their narrow base.
•Suitable for soft soils.
•Ellliptical sections can extra clearance
in in one direction while maintaining
structural integrity.

10. HORSE-SHOE CROSS
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.
•The horse-shoe shape provides better
clearance for vehicles and equipment
while still offering good structural
stability .
•Most suitable for soft rocks.

11. RECTANGULAR CROSS SECTION
•Suitable only in case of hard rocks.
•Constructed with RCC and used for pedestrial traffic.
•Difficult to construct.
•Costly
D- SHAPED (Segmental cross section)
•Suitable for subways and navigational tunnels.
•Segmental roof takes the external load and transfer
it to vertical side walls.
•Suitable for hard rocks.

12. Tunnel Boring Machine (TBM)
•A tunnel boring machine (TBM) is a highly specialized piece of
equipment used to excavate tunnels through various types of ground
conditions, from soft soils to hard rock.
•TBMs are equipped with a rotating cutting head at the front, which
breaks up the material in front of the machine as it moves forward. Behind
the cutting head is a system for removing the excavated material, which is
typically carried out via a conveyor belt or slurry pipeline. TBMs can vary in
size, from a few meters in diameter to large machines that create tunnels
wide enough for subways or roadways.

14. Key Components of a TBM:
1. Cutterhead: The rotating disc at the front, with sharp cutting tools to break through the materials.
2. Shield: Protects workers and machinery from falling material or cave-ins as the machine advances.
3. Conveyor System: Moves excavated material out of the tunnel.
4. Thrust System: Provides the force necessary for the TBM to move forward, typically using hydraulic
jacks.
5. Segment Erector: pre-cast concrete segments to line the tunnel as it advances.
Advantages of TBMs
•Safer and faster than traditional drilling and blasting methods.
•Creates smooth tunnel walls, reducing the need for additional lining.
•Minimizes disruption to the surface environment, especially in urban areas.
TBMs are essential for large infrastructure projects such as subway systems, railway tunnels, and
undersea tunnels.

15. There are several types of Tunnel Boring Machines (TBM), each designed for different geological
conditions. Here are the main types:
1. Earth Pressure Balance (EPB) TBM
Purpose: Used for soft ground, such as clay, silt, and sand, especially in urban environments.
Function: It controls the pressure at the tunnel face by using the excavated material to balance the ground
pressure. The spoil (excavated material) is compressed in a chamber before being transported out,
preventing ground subsidence or collapse.
Applications: Urban tunneling projects like metro systems, where surface disruption must be minimized.
2. Slurry Shield TBM
• Purpose: Ideal for water-bearing or unstable soils like sand, gravel, or soft ground.
• Function: Uses a slurry mixture (typically bentonite and water) to support the tunnel face, preventing the
collapse of loose material. The slurry is circulated, with spoil separated from it before the slurry is
recirculated.
Applications: River crossings, coastal tunnels, or other water-rich environments

16. 3. Hard Rock TBM
Purpose: Designed for tunneling through hard rock formations.
Function: Equipped with a rotating cutterhead that uses disc cutters to chip away the rock. These machines
don't require additional face support, as the rock itself typically holds the tunnel stable.
Applications: Mountain tunnels, deep tunnels through hard geological strata.
4. Gripper TBM (Open Type TBM)
Purpose: Suitable for stable, hard rock where no additional support is required.
Function: Uses extendable "grippers" to press against the tunnel walls to push the machine forward. It
doesn't have a shield, so it is best used in self-supporting rock conditions.
Applications: Long tunnels through hard rock, where temporary lining or shields aren't necessary.

17. 4.Hybrid TBM
• Purpose: Combines features of different types of TBMs to tackle complex geological conditions.
Function: Depending on the specific needs of the project, a hybrid TBM can alternate between EPB, slurry
shield, or hard rock modes.
Applications: Projects where ground conditions vary widely along the tunnel route.
Each type of TBM is optimized for specific geotechnical conditions, making them versatile tools for a wide
range of tunneling projects.