Especially for B.Sc. 4th Year

1. Tunnels and Tunneling
Date : May 23, 2020
Time : 1 : 00 P.M.
Especially for course of B.Sc. Fourth Year
ENGINEERING GEOLOGY
Presenter :
Sudhan Kumar Subedi
Meeting ID : 797 0719 4445
Meeting Password : 8CswQY
Interested can Join Zoom Meeting
https://us04web.zoom.us/j/79707194445?pwd=VHIxQU0rSGgvbWlvOUd1K2xaN2t6dz09
Basics on

4. May 23, 2020
Tunnels and Tunneling
Background
 It is understood that first tunnel was constructed by Egyptians and Babylon's about 4000 years ago. This
tunnel length – 910 m .
width – 360 cm
height – 450 cm
 Tunnels may be defined as the underground passages or routes excavated through the rocks or soft ground
without disturbing the overlaying rocks or soil covers.
 In Hindu Religion, in Mahabharat time, during Dwaparyuga, Pandavas get escaped through Tunnel in
Lakshagriha for being safe from fire burned by Duryodhan (Kauravs).

5. May 23, 2020
Tunnels and Tunneling
Background
According to local,
About 250 years ago,
Our ancestors used to
excavate the tunnels for
the mining activities for
making the coins in this
area. Due to the huge
over breakage of rock
during the excavation, 9
peoples died on site and
then it has been closed.

6. May 23, 2020
Tunnels and Tunneling
Background
 Tunnels are very important structures which are being used in various construction ; like in hydropower
project, mining activities, roads, railway for defence purpose and laying of pipelines etc.
Classified by Examples of Tunnels
Purpose Railway tunnels, metro system, highway tunnels, pedestrian tunnels, water
tunnels, sewage tunnels, services tunnels, storage tunnels
Geological
location/
condition
Rock tunnels, earth tunnels, submerged tunnels
Cross-sectional
shapes
Rectangular shape, circular shape, elliptical shape, egg shape, horse-shoe
shape and segmental shape
 Tunnels can be classified on the different basis as :

7. May 23, 2020
Tunnels and Tunneling
Background
 Tunnels have different shapes on the basis of their uses and the ground conditions and the availability of
materials.

8. May 23, 2020
Tunnels and Tunneling
Background
Hydropower Tunnel Hydropower Tunnel

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Tunnels and Tunneling
Background
Road Tunnel Railway Tunnel

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Tunnels and Tunneling
Background
Silver Mine Tunnel Copper Mine Tunnel

11. May 23, 2020
Tunnels and Tunneling
Geological conditions for Tunneling
 Tunneling is a serious engineering project.
 In addition to large investment cost, the challenges related to long and deep tunnels are the site
characteristics along the alignment routes.
 Geology plays a very important role in this. Any adverse and unforeseen geological conditions may
influence the safety of tunnels, loss of life, construction time and costs.
 When a tunnel or shaft is excavated, the rock stresses are perturbed around the opening and
displacements will occur.

12. May 23, 2020
Tunnels and Tunneling
Geological conditions for Tunneling

13. May 23, 2020
Tunnels and Tunneling
Geological conditions for Tunneling
 The physical context and key constraints that influence the planning of a tunnel alignment within
the project corridor are :
• geology;
• water courses;
• utilities;
• historic structures; and
• land use.
 The site geology provides the background setting for any underground engineering structure.
 The mechanical properties of the rock describe how the geologic materials deform and fail under the forces
introduced by the excavation.
 The geohydrologic conditions establish the quantity and pressure of water that must be controlled.

14. May 23, 2020
Tunnels and Tunneling
Geological conditions for Tunneling
 Geological/ geotechnical investigations are critical for proper planning of a tunnel.
 Selection of the alignment, cross section, and construction methods is influenced by the geological and
geotechnical conditions, as well as the site constraints. Good knowledge of the expected geological
conditions is essential. Tunnel alignment is sometimes changed based on the results of the geotechnical to
minimize construction cost or to reduce risks.
 The type of the ground encountered along the alignment would affect the selection of the tunnel type
and its method of construction.
 Study of the impact of geological features on the tunnel alignment in the presence of active or inactive
faults. During the planning phase, avoid crossing a fault zone. If it is un avoidable then proper measures for
crossing it should be implemented. Presence of faults or potentially liquefiable materials would be of
concern during the planning process.
 Geotechnical issues such as the soil or rock properties, the ground water regime, the ground cover over
the tunnel should be analyzed. The investigation should address not just the soil and rock properties, but
also their anticipated behaviors during excavation.

15. May 23, 2020
Tunnels and Tunneling
Geological conditions for Tunneling
 The investigation should also address groundwater. For example, in soft ground SEM tunneling, the
stability of the excavated face is greatly dependent on control of the groundwater. Dewatering, pre-
draining, grouting, or freezing are often used to stabilize the excavation.
 Analyzing the ground behavior during tunneling will affect potential settlements on the surface.
Measures to minimize settlements by using suitable tunneling methods or by preconditioning the
ground to improve its characteristics would be required.
 Risk assessment is an important factor in selecting a tunnel alignment. Construction risks. Sensitive
existing structures. Very Hard spots (rock, for example) beneath parts of a tunnel.

16. May 23, 2020
Tunnels and Tunneling
Site Investigation

17. May 23, 2020
Tunnels and Tunneling
Site Investigation

18. May 23, 2020
Tunnels and Tunneling
Site Investigation

19. May 23, 2020
Tunnels and Tunneling
Tunnel in Soft Ground
Types of Soft Ground
 Firm ground : roof can stand for few minutes and sides for much longer time ; eg, dry earth
 Soft ground : roof requires immediate support while sides can remain standing for few minutes
 Running Ground : required support immediately e.g. dry sand
 Self Supporting ground : remain unsupported up to short length of 1.5 to 4m; e.g. sandstone

20. May 23, 2020
Tunnels and Tunneling
Tunnel in Soft Ground
 Tunnels constructed in soft materials require temporary support immediately or shortly after excavation.
 There are various method to provide the support. They are :
- Suitably spaced bent of woods
Timber Support for Tunnel excavated in Highly Weathered Phyllite

21. May 23, 2020
Tunnels and Tunneling
Tunnel in Soft Ground
 Tunnels constructed in soft materials require temporary support immediately or shortly after excavation.
 There are various method to provide the support. They are :
- Suitably spaced bent of steel for lagging (covering)
Steel Ribs Installation in Super Madi Hydropower Project, Kaski

22. May 23, 2020
Tunnels and Tunneling
Tunnel in Soft Ground

23. May 23, 2020
Tunnels and Tunneling
Tunnel in Soft Ground
 Tunnels constructed in soft materials require temporary support immediately or shortly after excavation.
 There are various method to provide the support. They are :
- Liner Plates
Installation of Tunnel Liner Plate

24. May 23, 2020
Tunnels and Tunneling
Tunnel in Soft Ground
 Tunnels constructed in soft materials require temporary support immediately or shortly after excavation.
 There are various method to provide the support. They are :
- Fore poling placed to retain material between adjacent bents
Fore poling

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Tunnels and Tunneling
Water in Tunnel

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Tunnels and Tunneling
Water in Tunnels
After 45 days of construction

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Tunnels and Tunneling
Gases

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Tunnels and Tunneling
Gases

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Tunnels and Tunneling
Gases

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Tunnels and Tunneling
Temperature in Tunnel
 Temperature is an important factor in designing and maintaining tunnels, especially in cold regions
For example, the frozen damage is destructive to tunnels built in cold regions due to dramatic changes in
temperature
 The damage includes cracks, water leakage through the lining, and scrap of the main structures
 These destructive problems could potentially affect use and maintenance of tunnels. Therefore,
understanding tunnel temperature field is critical.
 The temperature distribution within tunnel lining and the surrounding rocks is also essential for the
analysis of stress and freeze-thaw effect.

31. May 23, 2020
Tunnels and Tunneling
Excavation of Tunnel
Cut and cover method
A method of tunnel construction involving the installation of earth support systems (e.g. slurry walls)
followed by the main excavation, placing of the base slab, roof slab and subsequent backfilling to the final
ground level.

32. May 23, 2020
Tunnels and Tunneling
Excavation of Tunnel
Sequential Excavation Method :
(Drilling and Blasting Method)
A method of tunnel construction that involves the use of standard construction equipment for excavation.
The tunnel is usually lined in two steps:
An initial lining of sprayed concrete provides immediate support and a subsequent secondary or
permanent lining is then placed using either sprayed concrete or cast insitu concrete.
A waterproof membrane is usually installed between the primary and secondary linings.

33. May 23, 2020
Tunnels and Tunneling
Excavation of Tunnel
Tunnel Boring Machine Method :
A method of tunnel construction that involves the procurement of a custom made piece of construction
equipment. The TBM is equipped with a cutter head that is used to mine the ground. The excavation is
continuously supported by installing precast concrete segments within the TBM and grouting them in place
as the machine advances.

34. Thank You !