12. History of Tunnelling
Shafts are the doorways to the underground tunnel, serving as the location at which all
material enters and exits. They vary in size and depth, and their design and construction
are key to the successful completion of any tunnelling project.
13.
14. Tunnels constructed in India
Atal Road Tunnel, Himachal Pradesh - Longest High-Altitude Tunnel Inaugurated on October 3, 2020
(Rohtang Tunnel) 8800 meters, Leh – Manali Highway, beneath the Rohtang Pass, Himachal Pradesh
Pir Panjal Railway Tunnel, Jammu and Kashmir (Longest Railway Tunnel)- Running across the heart of the
Himalayan ranges in Jammu and Kashmir, 11.22 km, Forest Block 185102, Pir Panjal Range, the Himalayas,
Jammu and Kashmir.
Dr Syama Prasad Mookerjee Road Tunnel, Jammu and Kashmir (Longest Road Tunnel) - Also referred to as
the Chenani Nashri Tunnel, the Patnitop Tunnel, or simply, the Syama Tunnel, the Dr Syama Prasad
Mookerjee Road Tunnel was inaugurated in the year 2017. 9.34 km. NH44 of Chenani, Jammu and
Kashmir.
Trivandrum Port Railway Tunnel, Kerala - second-largest railway tunnel in India. 9.02 km. Balaramapuram
Station, Kanyakumari – Thiruvananthapuram Railway Line, Kerala
Karbude Railway Tunnel, Maharashtra - 6.5 km, Ratnagiri, close to the Western Ghats in Maharashtra.
Natuwadi Railway Tunnel, Maharashtra - second-longest tunnel in the Konkan railway line, 4.39 km. The
Tunnel connects Karanjadi and Diwan, while also passing through Goa
25. Tunnels in rock-masses are usually constructed by the bored tunnel technique. Both the
conventional and the mechanized methods are used and the selection depends on the tunnel's
length and the rock's characteristics.
Bored method : The tunnel is constructed inside the earth using excavating techniques that
either involve: i) blasting, ii) mechanical excavators (conventional method), or iii) mechanized
excavation using Tunnel Boring Machines (TBM’s).
Conventional Tunnelling can be defined as the construction of underground openings of any
shape with a cyclic construction process composed of the following steps:
•excavation, by using the drill and blast methods (explosives) or very basic mechanical
excavators
•mucking
•placement of the primary support elements such as:
•steel ribs or lattice girders
•soil or rock bolts
•sprayed or cast in situ concrete
Tunnelling in hard rock
28. Due to the looseness and low viscosity of the flowing sand, after excavation, the sand
body is easy to flow along the open surface. In addition, the water seepage also causes
tunnel instability.
At the top position of the tunnel, a vertical vacuum negative pressure precipitation
method of intercepting the top seepage water and the water supply behind the top of the
tunnel is usually considered.
For the bottom of the tunnel, setting gravity wells on the side walls for the purpose of
preventing seepage at the bottom was usually considered.
The application of these methods in the project ensured the safety of construction and
improved the construction schedule.
29. Shallow-depth tunnels, such as large sewer
tunnels, vehicular tunnels, and rapid transit
tunnels, are frequently designed as structures to
be constructed using the cut-and-cover method.
Tunnel construction is characterized as “cut-and-
cover” construction when the tunnel structure is
constructed in a braced, trench-type excavation
(“cut”) and is subsequently backfilled (“covered”).
For depths up to 35–45 ft this method is often
cheaper and more practical than underground
tunneling, and depths of 60 ft or more are quite
common for rapid transit cuts.
Cut and cover tunnels
30. Underwater tunnel
An underwater tunnel is a tunnel which is partly or wholly constructed under the sea or a
river. They are often used where building a bridge or operating a ferry link is unviable, or
to provide competition or relief for existing bridges or ferry links
East West Metro
Tunnel is a constructed
underwater river tunnel
of Kolkata Metro in
Kolkata, West Bengal.
The river tunnel is
constructed underneath
Hooghly River. It is the
biggest underwater river
tunnel of India, which is
made for metro rail
service.
32. D-Shaped Tunnels
Where the risk of failure or collapse caused by external pressure from water or loose
unstable soil conditions on tunnel lining is non-existent, these types of tunnel roof also
called segmented roof takes up all the load and distributes it to the straight walls.
33. It is a section with an arched roof and
straight sides. These are generally used
for subway or navigation tunnels.
Advantages:
•It is the most suited in rock tunnels.
•It is suitable to resist external load due
to its arch-shaped roof.
•It has a flat floor which is helpful for
driving and moving any equipment.
34. Circular Shaped Tunnels
Circular tunnels are used to carry water under pressure. These are not appropriate for
traffic tunnels because more filling is needed to make the base flat.
35. Tunnels are often constructed with a circular
cross section because this shape is the most
efficient at withstanding the pressure of the
surrounding soil or rock.
The circular shape distributes the pressure
evenly around the tunnel, making it more
stable and less likely to collapse.
Additionally, a circular cross section allows for
easier excavation and reduces the amount of
material needed for construction compared to
other shapes.
Overall, the circular cross section is a practical
choice for the structural integrity and cost-
effectiveness of tunnel construction.
36. Rectangular Shaped Tunnels
For pedestrian traffic, rectangular shapes of tunnels are appropriate. These tunnels are
sometimes accepted if pre-constructed R.C.C caissons are used. These types of tunnels are
not suitable to resist external pressure due to their rectangular shape and these are not in
use these days.
37. Advantages of Rectangular Tunnels
1.More Space for Movement – Rectangular tunnels provide more space for movement than
circular tunnels of the same area. This means that rectangular tunnels can accommodate
larger vehicles or more pedestrians, which is particularly useful in urban areas where space is
at a premium.
2.Better for Utilities – Rectangular tunnels are well-suited for housing utilities such as pipes
and cables. The flat walls and floor of a rectangular tunnel make it easy to install and maintain
utilities, which can reduce the cost and time required for repairs and upgrades.
3.Safer for Vehicles – Rectangular tunnels have a lower risk of vehicle rollover than circular
tunnels of the same area. This is because the flat walls of a rectangular tunnel provide a more
stable surface for vehicles to travel on, reducing the risk of accidents and improving safety for
drivers and passengers.
4. More Versatile – Rectangular tunnels are more versatile than circular tunnels, as they can
be used for a wider range of purposes. In addition to transportation and utilities, rectangular
tunnels can be used for storage, pedestrian walkways, and even as event spaces.
38. Rectangular tunnels have a higher degree of utilization of underground space and a lower
volume of earthwork excavation; thus, a rectangular tunnel is often a valid option due to
the development of advanced tunneling machines.
Rectangular tunnels are suitable for shallow depths in weak ground as they have lesser
settlement compared with circular tunnels. This is crucial for tunneling beneath
important structures such as railway lines and existing roads.
Disadvantages of Rectangular Tunnel
1.Higher Cost – Rectangular tunnels are often more expensive to construct than circular
tunnels of the same area. This is because rectangular tunnels require more materials and
labor to construct, as well as additional support structures to maintain their shape.
2.Limited Drainage – Rectangular tunnels have limited drainage capabilities compared to
circular tunnels. This means that in areas with high rainfall or flooding, rectangular tunnels
may be more prone to flooding and water damage.
3.Difficulties with Ventilation – Rectangular tunnels can be more challenging to ventilate
than circular tunnels. This is because the flat walls of rectangular tunnels create more air
resistance, which can make it harder to maintain adequate airflow for ventilation.
39. Elliptical Shaped Tunnels
These are suitable for softer materials. For better resistance to external pressure, the major
axis of these tunnels is maintained vertically. The section is narrow at base, so cannot be used
for traffic applications. It is best suited for carrying water and sewage.
40. Horseshoe Shaped Tunnels
A horseshoe-shaped tunnel is a combined shape of arches and circular tunnel. These types
of tunnel shapes are quite popular. It has a semi circular roof together with arches, sides and
a curved invert.
41.
42. Egg-Shaped Tunnels:-
Egg shaped tunnels suitable for sewage
lines as they have self cleaning velocity in
dry weather, egg shaped tunnels can
resist external as well as internal
pressure.
The narrow cross section at the bottom
forms the shape of an egg.
Not considered for traffic applications
because of the narrow shape at the base
