Geology of Tunnels, Lining of Tunnels etc.

1. Tunnelling
Geology of Tunnels, Lining etc.
(ENGINEERING GEOLOGY)
LECTURE – 12
Instructor: Engr. Naeem Bashir AwanHITEC, University

2. Outline
1. Tunnels
2. Purposes of Tunnels
3. Types of Tunnels
4. Geological Considerations
5. Engineering Geology of Tunnels
6. Lining of Tunnels
7. Cross Sections of Tunnels

3. Tunnels
Tunnel is an underground passageway, dug through the
surrounding soil/earth/rock and enclosed except for entrance
and exit, commonly at each end.

4. Purposes of Tunnelling
 For facilitating rail and road traffic
 For public utilities
 For power generation
 For mining activities
 For diverting water during dam construction

5. Different Types of Tunnels
Tunnels are of different types and usually classified on the basis of
a) Type of lithological material through which tunnel is constructed.
b) The type of application for which the tunnel was constructed.
c) The alignment of tunnel

6. Different Types of Tunnels
Classification of Tunnels based on Lithological materials
a) Tunnels through Hard Rocks
b) Tunnels through Consolidated Soils
c) Tunnels Through Unconsolidated Soils
d) Tunnels through Water Bodies

7. Classification based on Lithological Materials
a) Tunnels through Hard Rocks
 Very expensive drilling
 Required high explosives and detonating explosives
 Time taken
 Very good natural lithological support
 Tunnel roof required no support after excavation
 Safe against seismic and hydrologic factors

8. Classification based on Lithological Materials
b) Tunnels through Consolidated Soils
 Easy drilling
 Not required any explosives or detonator for tunneling
 Tunnel roof required support after excavation
 Unsafe against seismic and hydrologic factors.

9. Classification based on Lithological Materials
c) Tunnels through Unconsolidated Soils
 Very easy drilling
 Not required any explosives or detonator for tunneling
 Tunnel roof required instant support after excavation
 Very unsafe against seismic and hydrologic factors.

10. Classification based on Lithological Materials
d) Tunnels through Water Bodies
 Very complicated drilling process based on the type of lithology required
explosives and detonator for tunneling.
 Tunnel roof required instant support after excavation.
 Very unsafe against seismic and hydrologic factors.

11. Classification based on Purpose/Application
a) Traffic Tunnels
 There are different types of traffic tunnels like Road Tunnels, Railway
Tunnels, Subway Tunnels, Navigational Tunnels, Pedestrian Tunnels etc.
 All these types of tunnels vary design, construction material, methods and
construction cost.
 The shape and size of these tunnels also considerably vary with each
other.

12. Classification based on Purpose/Application
b) Conveyance Tunnels
 Conveyance Tunnels are designed for specific applications. These types of
tunnels are Hydropower Tunnels, Water Supply Tunnels, Sewerage
Tunnels, Industrial Tunnels for passing toxic industrial effluents etc.
 These tunnels provides safety and conveyance in several industrial and
engineering applications.

13. Classification based on Alignments
a) Slope Tunnels
 These Tunnels are constructed at the foot hills of the mountains and
slope.
 These type of tunnels are constructed for railway and highway routes to
provide safe transportation and protection against landslides and
mudflows.

14. Classification based on Alignments
b) Spiral Tunnels
 These type of tunnels are formed at narrow valleys and are usually form
loops within the mountains.
 These tunnels are spiral in shape and provide safe passage in high
mountain ranges.

15. Geological Considerations
 Types of Rocks
 Geological Structures
 Ground Water Conditions
 Overbreak

16. Geological Considerations
 Before starting any underground tunnel excavation project, realistic geological
site investigations are essential.
 Geological investigation provides maximum information about the rock
characteristics, existing structural systems within the body of rock and ground
water conditions.
 Such information’s are extremely important for the tunnel designers. These
information’s enable Engineers and Geologists to anticipate the behaviour of the
rocks and type of support required to maintain the tunnel in a stable condition.

17. Geological Considerations
 Geological information is also important for deciding the optimum tunnelling
method and type of site improvement method required.
 In low topographic relief areas tunnels are built in shallow depth and the cost of
drilling is relatively low.
 Several geophysical techniques are used for subsurface comprehensive site
investigations.

18. Geological Considerations
Tunnelling through Soft Rocks:
 Majority of the sedimentary rocks are soft rocks. These rocks are poorly
compacted and usually have high porosity and permeability as compared to the
igneous and metamorphic rocks.
 Some of the common soft rocks are shale, limestone, sandstone, chalk and
dolomites. The excavation in soft rock is easy and less costly as compared to
hard rocks but tunnelling through soft rocks is always dangerous as these rocks
are not self supporting and very sensitive to weathering and erosion.

19. Geological Considerations
Tunnelling through Soft Rocks:
 Therefore in soft rocks along with the excavation temporary and permanent
support is needed at excavated regions to avoid caving from roof and other sides
of tunnel structure. Such arrangements are costly and time taking.
 If the soft rocks are fractured or jointed as a result of folding or faulting then
tunnelling becomes extremely dangerous and tunnel excavation through such
rocks required large scale temporary support which is followed by permanent
lining.

20. Geological Considerations
Tunnelling through Hard Rocks:
 Most of the igneous and metamorphic rocks comes under the hard rock
category. Some common rocks under this category are granite, basalt, syenite,
Gabbros, quartzite, gneiss, marble etc.
 Tunnelling through these rocks are always safe because the rocks are self
supporting and less sensitive to weathering and erosion.
 The excavation in hard rocks is costly and is carried out by control blasting
methods and tunnel boring machines (TBMs). These rocks are considered as
favourite rocks in Tunnelling.

21. Geological Considerations
Essential Geological Investigations in Tunnelling:
 The thickness and orientation of the stratified layers within the rocks.
 The crystal structures and grain size of rocks.
 Porosity and permeability of the rocks at the construction site and surrounding
areas.
 Bearing and Tensile strength of rocks at various tunnel sections.
 Water table conditions at construction site and surrounding areas.
 Seismic activities and hazards in the region.
 Soil types and bulk densities of the rocks.

22. Geological Considerations
Essential Geological Investigations in Tunnelling:
 Possibility of occurrence of hazardous gases at the tunnel excavation site.
 Drainage pattern and safety against flood peak situations.

23. Lining of Tunnels
Tunnels in loose rock and soft soils are liable to disintegrate and, therefore, a lining
is provided to strengthen their sides and roofs so as to prevent them from
collapsing. The objectives of a lining are as follows.
 Strengthening the sides and roofs to withstand pressure and prevent the tunnel
from collapsing.
 Providing the correct shape and cross section to the tunnel.
 Checking the leakage of water from the sides and the top.
 Binding loose rock and providing stability to the tunnel.
 Reducing the maintenance cost of the tunnel.

24. Lining of Tunnels
Shape of tunnel depends on the ground conditions and the method of construction. At the
same time, only certain shapes can be adopted for certain method of construction. Most
common shapes of a transportation tunnel and adopted method for the shape are listed below
Strengthening the sides and roofs to withstand pressure and prevent the tunnel from
collapsing.
 Rectangular or square Tunnels – > Cut and cover tunnels and jacked box tunneling.
 Circular tunnels – > Tunnel boring machine (TBM) or by drill and blast in rock.
 Horseshoe tunnels -> Drill and Blast in rock, Sequential Excavation Method (SEM) and
New Austrian Tunneling Method (NATM)

25. Lining of Tunnels
Sequence of Lining:
The lining of a tunnel is done in the following steps.
1. In the first stage guniting is done to seal the water in rock tunnels.
2. Concrete lining is done either in one attempt as in the case of circular tunnels or by
separately tackling the vest, the sidewall, and the arch. For small tunnels that measure 1.2
to 3.0 m in diameter, the concrete lining can be provided by the hand placing method. In
the case of bigger tunnels, concrete pumps or pneumatic placers are used for placing the
concrete.
3. The concrete is cured to its maximum strength. If the humidity inside the tunnel is not
sufficient, curing can be done by spraying water through perforated pipes.

26. Lining of Tunnels
Types and Thickness of Lining:
 In practical terms the lining provided most commonly is that of reinforced
concrete or concrete surface.
 Concrete lining is provided in tunnels because of
a) Its superiority in structural strength,
b) Ease of placement,
c) Its durability,
d) Lower maintenance cost.

27. Lining of Tunnels
Types and Thickness of Lining:
 In practical terms the lining provided most commonly is that of reinforced
concrete or concrete surface.
 Concrete lining is provided in tunnels because of
a) Its superiority in structural strength,
b) Ease of placement,
c) Its durability,
d) Lower maintenance cost.

28. Cross Sections of Tunnels

29. Name of Tunnels Short Description
Khojak Tunnel
(Sheela Bagh Tunnel)
(Balochistan)
3.91 kilometers (2.43 miles)
(Railway Tunnel)
Lowari Tunnel
(KPK)
10.4 kilometers (6.5 miles)
(Vehicular Tunnel)
Attabad Tunnels
(Gilgit Baltistan)
7 kilometre long Five Vehicular
Tunnels

30.  HITEC University, Taxila
The End
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