Tunnel Engineering.pptx

Tunnel Engineering
Ms. P.S.Mane

content
• Tunnel Engineering: Introduction to tunneling
• Size and shape of tunnel and suitability
• Tunneling in hard rock, and soft material
• Shield method
• Safety measures
• Ventilation, lighting and drainage of tunneling

Tunnel
Definition of Tunnels: A tunnel is an Engineering structure, artificial
gallery, passage or roadway beneath the ground, under the bed of a
stream or through a hill or a mountain.
▣ Open Cut
Open to sky passage excavated through huge soil mass of obstacle in
required directions to connect two roads or railways
▣ Bridge
Over-ground construction to cross over obstacles without disturbing the
natural way below it

Types of Tunnels
◾An underground passage for
• Road or rail traffic
• Pedestrians
• Utilities
• Fresh water or sewer
( Ratio of length to width is at least 2: 1 ,Must be completely enclosed on all
sides along the length)
◾Based on purpose (road, rail, utilities)
◾Based on surrounding material (soft clay vs. hard rock)
◾Submerged tunnels

Advantages & Disadvantages of Tunnel
Advantages of Tunnel
1. For carrying public utilities like water or gas, Railway lines or roads across a stream
or a mountain.
2. Tunnels are cheaper than Open cut.
3. Tunnels avoid the dangerous open cut adjacent to the structure.
4. Cost of hauling is decreased due to lighter grades possible in Tunnel.
5. Aerial warfare and bombing of cities have given intangible value to Tunnels.
Disadvantages of Tunnel
1. Construction of Tunnels requires long time in completing as compare to open cut.
2. Specialized equipments and methods make tunnel costlier than open cut.

Shape and Size of a Tunnel
The shape and size of tunnels depend upon the following factors:
1. The shape of section best suited to the condition.
2. The interior dimension of the section.
Shape of Section: The shape of the sectional profile should be such that the
lining is able to resist the pressures exerted by the unsupported walls of the
tunnel excavation. These pressures are both lateral and vertical in direction
and vary with the character of the material penetrated i.e. Cohesion and
internal friction. The sectional profile of a tunnel should be designed to offer
greatest resistance at its highest points. The curve must therefore be sharper
at the crown and may decrease towards the base.

The commonly adopted
Sections are:
1. Horse – shoe Section
2. Circular
3. Egg shaped
4. D or Segmental Roof Section
5. Rectangular or box type
▣ Horse – shoe Section
• Semi-circular roof with arched sides and curved invert
• Best shape for traffic purposes Most suitable for soft
rocks and carrying water or sewage
• Most widely used for highway and railway tunnels

Circular Section
Advantages :
1. This type of tunnels are best for resisting internal or external
pressures.
2. It provides the greatest cross-sectional area for the least
parameter.
4. This type of tunnels are used for water and sewer conduits.
5. Best suitable to construct in non-cohesive soils.
Disadvantages:
1. It requires lot of filling for Railways and roadways.
2. This shape is more difficult for placement of concrete lining.

D or Segmental
Roof Section
• Suitable for sub-ways
or navigation tunnels
• Additional Floor
Space and flat floor

Rectangular & Egg shaped
▣ Rectangular Section Suitable for
hard rocks
• Adopted for pedestrian traffic
• Costly & difficult to construct
▣ Egg shaped Section Carrying
sewage
• Effective in resisting external and
internal pressures

Preliminary
considerations
of a tunnel

Preliminary considerations of a tunnel
The selection of a tunnel type depends on the geometrical configurations, the ground
conditions, the type of crossing, and environmental requirements.
Spoon samples should be taken for soil classification, and undisturbed samples, where
possible, for laboratory testing. Density, shear and compressive strength, and plasticity
of soils are of special interest. All borings should be carried below tunnel invert. For
pressure face tunnels, borings should be located outside the tunnel cross section.
For rock tunnels, as many borings as practicable should be made. Holes may be
inclined, to cut as many layers as possible. Holes should be carried below the invert
and may be staggered on either side of the center line, but preferably outside the
tunnel cross section to prevent annoying water leaks. Where formations striking
across the tunnel have steep dips, horizontal borings may give more information;
borings 2000 ft in length are not uncommon.
All cores should be carefully cataloged and preserved for future inspection. The ratio
of core recovery to core length, called the rock quality designation (RQD), is an
indicator of rock problems to be encountered.

Geological Investigations:
This investigation refers to conduct accurate and detailed geological survey of the
locality. The geological knowledge can be used in preparing a geological map showing
character of material, presence of water, different strata and their inclination.
Character of Material-The material can be classified in the following categories:
1. Hard rock: These are the rocks having sufficient cohesion to stand vertically when cut
to any depth. Many of the primary rocks like granite, feldspar and basalt belong to this
class. Hard rocks can be classified into two categories viz hard rocks unaffected by the
atmosphere and those which are affected by the atmosphere.
2. Soft rock: Soft rocks are those in which the force of cohesion is less than in hard rocks
and which offer less resistance to attacks to breakdown their original structure. These
rocks are also affected by the atmosphere. These rocks are to be supported by the
timbering during excavation and need strong lining to exclude the air and to support the
pressure and prevent fall of fragments.

3. Soft Soils: These soils composed of detrital materials having so little
cohesion that they may be excavated without the use of explosives.
Tunnels excavated through these soils may be strongly timbered during
excavation to support the vertical pressure and prevent caving. Gravel,
sand, clay, peat etc are commonly encountered soft soils.
4. Ground water presence: If an exploration indicates presence of
significant quantities of ground water, it may be desirable to seek a
more favorable location or if it is not possible, pressure grout ahead of
the formation may be necessary as a mean of reducing the flow of
water.

Important Rock Properties to be considered during
Geological Investigations
• The orientation of rock stratification.
• The thickness of individual layers, the regularity of sequence of layers.
• Mineralogical composition.
• The bond between the individual grains.
• The hardness, workability of drills.
• The Structural form of rocks.
• Internal structure.
• Bearing and tensile strength at various tunnel sections.
• The possiblity of occurance of harmful gases.
• Safety against air-escape in compressed air tunneling.
• Rockfalls, slides and other hazards to structure.
• After the results explorations are analyzed, the location that will permit the construction of a
satisfactory tunnel at the lowest practical can be selected.

Steps for Surveying in Tunnels:
• Locating the Center line on the ground
• Transferring Center line to inside of Tunnels
1. Locating the Center line on the ground:
In short tunnels the center line may be accurately located by means of a
common theodolite, on a calm and clear day. Wooden stakes are employed
to mark the points, temporarily The observations are checked and rechecked
and wooden stakes are then replaced by permanent monuments of stone or
concrete.
In Long tunnels, the theodolite employed must be of large sized Micrometer
Transit theodolite. The line is located by means of Triangulation. The various
operations must be performed with the greatest accuracy and repeated to
reduce the error to minimum. The center line is then marked on permanent
mountains.

Transferring Center lines to inside of Tunnels:
• The centerline located on the ground surface
can be transposed to the inside of the
tunnel, to direct the excavation in the
following manner.
• Let X and Y be the entrances and x and y be
the two distinct fixed points which have
been ranged in with the center line located
on the ground surface over the hill XYZ. The
instrument is set up at T, any point on the
line XX produced and a bearing is taken by
observation on the center line marked on
the surface.

The bearing is then carried into the tunnel by plunging the telescope and setting
pegs in the roof of heading. lamps hung from these pegs furnish the
necessary sighting points. The same procedure is used for the other end of the
tunnel tille excavation extends further into the hill, line is run from the points
marked on the roof of the heading. Great accuracy is required.
In case of Long tunnels the working is driven from several points at one time by
means of shafts. In these cases to direct excavation, it is necessary to fix
the centre line on the bottom of the shafts. This is accomplished in two ways
1. When shaft is located directly over center line
2. When shaft is located to one side of centre line.

Shafts
• Shafts are vertical wells along the line of a tunnel at one or
more points, between the entrances, to permit the tunnel
excavation to be attacked at several points at the same
time. Each shaft opens two additional faces to work. By
opening the additional faces for attack, they expedite the
construction work and also provide openings for removal
of the excavated material.
• Shafts can also be used for pumping out the water and to
achieve adequate ventilation in the tunnel. During the
construction shafts serve the same purpose as the
entrances hence they must afford passageway for
construction tools, workmen, machinery, hoisting of muck
and pipes for ventilation, water and compressed air.

Size of a Shaft:
The size of a shaft depends on the following factors:
1. Amount of muck to be hoisted.
2. Hoisting system adopted.
3. Size of muck car.
4. Number of workmen.
5. Space required to carry pipe and wiring.
6. Type of construction equipment to be used.

According to the position shafts are classified as follows
1. Shafts over centre line: In this category shafts are made directly
over the centre line of the tunnel. The advantage of this type is
great facility which it affords for hoisting out the material.
2. Side Shafts: Side shafts are those which are not made directly
over the centre line but are shifted to one side, requiring a
transverse gallery connecting it with the tunnel. The only
disadvantage of this type is that side gallery necessitates turning of
machine at sharp curve.

Classification of Shafts
1. Inclined Shafts: These shafts are used when the depth is small. The excavation of
such shafts proceeds in the upward direction. The excavated material falls downward
and is removed the tunnel. Removal of muck by gravity is achieved by using suitable
gradient of 45 degrees or less.
2. Vertical Shafts: These shafts are usually easier and cheaper to excavate then
inclined shaft. In some cases a pilot shaft is first driven upward before the shaft is
excavated to full sectionin the downward direction. The pilot shaft is used for muckling
out. The widening of the shaft to full to full size proceeding downwards. Shafts may be
either :
Temporary Shafts : Those shafts which are filled in after the construction of tunnel is
completed.
Permanent shafts: Those shafts which are left open, after the construction of tunnel is
over to provide ventilation in the tunnel.
3. Circular Shafts: These shafts are lined with prestress steel linear plates or concrete.
Permanent shafts are usually circular in shape.

Methods of Timbering
1. For timbering in small shafts in soft ground a hole of about 15 cms deep is dug
and in this hole two sets of timber are assembled, plumbed and braced with
diagonals. Excavation uinder the bottom of the sheeting is then started keeping
the sides vertical sheeting is driven down. Another set of Sheeting is started
within the timbers of first set. Slight margin is given to the second sheeting which
is closed by nailing short boards. Using this system Shafts upto 17 m or more have
been sunk. Where depth of shaft is great forepoles 1.5 to 1.8 m or long are used
to support the ground.
In firm soils like clay excavation may be done upto 3 m or so and planks of wood
are set against the trimmed walls where they are held untill other timbers are
placed. Shafts may then be deepened in stage of 1.5 m or so and walls suitably
lagged and wedged to ensure that every plank is tight against the ground. Pressed
linear plates are also used for lining the shafts.

the second method involves excavation of a pit into which are built a number of
complete rings of segmental cast iron, cast steel or reinforced concrete lining. This
pit may be taken to a depth of two to three rings of the lining or more depending
upon the stablity of the ground. Shaft sinking is continued by excavating center of
the hole, under cutting the lining already erected and erecting further segments
of the lining. Thus buildng up additional rings. Space behined the lining is filled
with grout.
3. In some cases it is possible to drive a ring of steel sheet piling through the first
7 metres or so on the ground and after excavating the material inside built the
first section of the shaft inside this.
4. In soft or water bearing grounds it is usually more ecnomical to build the rings
in the form of a cassion commencing generally at ground level. The first ring has a
V shaped bottom forming a cutting edge. On the top of it normal rings are
erected, unitll it is heavy enough to sink into the ground. The rings are normally
built up from cast iron or reinforced concrete segments.

Drills and drilling in tunnels
Rocks are loosned by drilling holes and filling them with explosives and firing them.
Before charging and firing the blast holes an effective pattern of drill holes is drilled for
maximum excavation of rocks.
Theory of drilling and Blasting
A drill hole norrmal to face when exploded with proper charge will break out a gap
inclined at approx. 45 degree to the face. If two similar holes are kept side by side and
fired togeter they will break the ground with increased number of holes, the quantity
of rocks displaced considerably increases.
An inclined cut hole is more effective as the explosive acts normal to the axis of the
hole. Most efficient angle for a cut hole is 45 degrees.
Drilling Equipment
Purposes for which drilling are performed vary a great deal from general to
highly specialized applications. It is desirable to select the equipment and methods
that are best suited to the specific service

Types of Drills:
1. Abrasion type drill: This drill grinds rock into small particles through the abrasive
effect of a bit that rotates in the hole.
2. Blast-hole type drill : This is a rotary drill consisting of a steel-pipe drill stem on the
bottom of which is a roller bit that disintegrates the rock as it rotates over the rock.
The cuttings are removed by a stream of compressed air.
3. Churn: The chum drill is a percussiontype drill consisting of a long steel bit that is
mechanically lifted and dropped to disintegrate the rock. It is used to drill deep holes,
usually 6 in. in diameter or larger.
4. Core: This drilling equipment is designed for obtaining samples of rock from a hole,
usually for exploratory purposes. Diamond and shot drills are used for core drilling.
5. Diamond: The diamond drill is a rotary abrasive-type drill whose bit consists of a
metal matrix in which a large number of diamonds are embedded. As the drill rotates,
the diamonds disintegrate the rock.
6. Dry: This is a drill which uses compressed air to remove the cuttings from a hole

7. Percussion: This is a drill which breaks rock into small particles by impact from
repeated blows. It can be powered by compressed air or hydraulic fluids.
8. Shot:: This is a rotary abrasive-type drill whose bit consists of a section of steel pipe
with a roughened surface at the bottom.
9. Wagon: This is a drifter mounted on a mast supported by two or more wheels.
10. Wet: A wet drill is one that uses water to remove the cuttings from a hole.
11. Jackhammer,or sinker: This device is an air-operated percussion-type drill that is
small enough to be handled by one worker.
12. Fusion Piercing: This is the latest method for drilling holes for blasting purposes.
Fusion piercing is produced by burning a mixture of oxygen and a flux bearing fuel
such as kerosine at the end of a blow pipe. When the flame is directed against the rock
the high temperature of about 4000 F causes rock to spall or flake off. The flux in the
fuel causes other types of rock to melt.

Factors afecting selection of Drilling equipment
1. The purpose of the hole such as blasting, grout injection etc
2. The size and required depth of the hole
3. The nature of the terrain.
4. The type and hardness of the rock.
5. The extent to which the rock is broken or manufactured.
6. Overall size of the project.
7. Availability of water for drilling purpose. Lack of water may result in dry drilling.
8. The extent to which rock is to be broken for handling.

Explosives used in Tunnels
Blasting is the operation performed to loosen rocks so that it may be excavated o removed from its
existing position. Blasting is accomplished by discharging an explosive that has been placed in a hole
specially provide for this purpose.There are many types of explosives but they all pretty much fit into
four main groups, Primary, Low, High, and Blasting Agents. Each of these groups is used for different
things including blasting, military use, demolishing, and excavating.
Primary Explosives
Primary, the first of the four main groups, is not as well known as the other groups, but is still used
commonly. Primary explosives aren¹t usually used as the main explosive itself, but as a detonator. They
are good detonators because they are very sensitive to the heat of fuses. Common primary explosives
are lead azide, lead stiphnate, and mercury fulminate. They aren¹t very extravagant, but they do the job.

Low Explosive
An explosive which utilizes chemical formulas which combust when a certain amount
of initial energy is applied to them. The rate at which the pyrotechnic composition
burns is mostly dependent upon the rate at which the composition can transfer heat
from one layer of itself to another. When a composition's rate of reaction is very slow,
it is known as burning.

High Explosive
• High explosives,the most stunning of the groups, is very unique. With greater power and less
sensitivity than the others, high explosives are the perfect explosive for blasting and excavating.
Nitroglycerin, the most powerful and sensitive of all the explosives, was the first high
explosive. Another type of high explosives is pentolite (PETN TNT). PETN (pentaerythritoltretrinitrate)
is the final high explosive, which is used in detonating caps and fuses.High explosives are stunning,
but powerful and deadly. A device in which the explosive composition will detonate once
initiated. High explosives can be initiated in several manners. The burn rate is now dependent upon
how well the explosive composition can transfer the detonation wave (shock wave) through itself. A
salute must be large enough to allow for a shock front to be formed in order for a detonation to
occur. A detonation releases a great amount of energy in a very short period of time, hence the reaso

Blasting Agents
Blasting agents, the final group of explosives, is the most peaceful because they are not used in military
weapons, yet they are very powerful and are used in mining and excavating. Blasting agents aren¹t used in
military weapons, but mining and excavating instead. These are inexpensive, yet safe and powerful.
Dynamite, a mixture of nitroglycerin and kieselguhr(which is made of tiny sea animals bones), is the most
well known blasting agent. Dynamite does what it¹s made to do, and well, It blasts.
Transporting and handling of Explosives
The following shall be the minimum requirements for the handling of explosives:
a) Safety distances/fire prevention. Smoking is not permitted when handling explosives or within 30m of
explosives.
b) Security. Explosives shall be guarded at all times. The only exception to this is after explosive charges have
been laid, however in that case the danger area shall be secure.

c) Only suitably qualified personnel shall handle or use explosives for demolition tasks.
d) Unqualified personnel shall only handle explosives for administrative tasks and under the supervision
of a person trained in either, the handling and storage of explosives, or a person trained in the handling
and transport of explosives.
e) Unqualified personnel required to handle explosives shall be briefed on the safe handling of
explosives and the safety precautions to be observed in and around explosives, explosive stores and
explosive vehicles.
f) Handling. Explosives shall only be handled in accordance with the manufacturers’ instructions and
specifications.
g) Clothing. Clothing worn by personnel handling explosives shall not be of a type that may cause
sparks. This includes synthetic clothing and boots with steel hobnails or toecaps.

Driving Tunnels in rock
Tunnel construction in rocks differs from tunneling in soft grounds:
1. Operation of tunneling in rocks is costly.
2. Greatest care is required while tunneling in hard rocks.
3. Any over cutting will entail heavy expenditure in resectioning
4. Rocks being self supporting require lesser timbering for supporting.
5. Tunneling in rock allows construction operations in many sections along the length of the tunnel, thus
expediting the wqork.

Sequence of Operations
• For a tunnel driven through rock the following operations are usually involved
• Setting up and drilling.
• Loading holes and shooting the explosives
• ventilationa and removing dust of explosion.
• Loading and hauling of muck.
• Removing ground water (if any)
• Erecting supportng timbers for sides and roofs if necessary.
• Placing reinforced steel.
• Placing concrete lining.

Methods of Tunneling in Rocks
The popular methods for tunneling in rocks are:
1. Full Face Method
Full face method means the whole section of the tunnel is attacked at the same time. It is suitable for tunnels of ssmall
cross section area say upto 3 m diameter. With the devlopment of Jumbo or drill carriage this method is frequently used.
Advantages
1. As full section has to be tackled, the work is expedited.
2. Muckling track can be laid progressively along with the tunneling.
3. Tunneling is continous.
Disadvantages
1. Full face atack requires heavy mecanical equipment.
2. Method may not be possible for the unstable rocks.
3. Limited for short spans.

2. Heading and Bench Method
This method involves the driving of the top portion in advance of the bottom portion. It is used when
tunnel section is very large and quality of rocks is not very satisfactory.
In self supporting rocks Top heading advances one round ahead of the bottom heading.
If rock is broken and not self supporting bench provides platform for timber supports to the heading.
When bad ground is encountered longer headings 25m to 35m are provided and roof arch supported by
shuttering as above. If the heading holes are properly loaded most of the muck will be thrown off and
the rest is cleared by hand labour.
Advantages
1. Simultaneous drilling and muckling is possible.
2. Requires less powder than in full face method.

Driving tunnels in Soft grounds
Hard Rock or fully self- supporting but Soft Soils – requiring temporary supports during and after
construction.
▣ Running ground – needing instant support all around- Water Bearing sands and cohesion-less soils
▣ Soft ground - instant support for roof like soft clay
▣ Firm ground – roof will stand for a few minutes and sides for a much longer period- Firm clay
and dry earth
▣ Self supporting ground – soil stands supported for a short period and for short lengths of 1200 mm
to 5000 mm – sandstones , cemented stones

Methods
1. The English method
2. The Austrian (cross-bar) method
3. The German method (core-leaving method)
4. The Belgian system (underpinning or flying arch method)
5. Cut and Cover Method

Tunnel Shielding
a protective structure used in the excavation of tunnels through soil that is too soft or fluid to remain
stable during the time it takes to line the tunnel
developed by Sir Marc Isambard Brunel to excavate the Thames Tunnel beginning in 1825
◾Types of Shield Tunneling
Manual
Tunnel Boring Machine (TBM)
🢝 Front end: Rotating cutting wheel
🢝 Middle portion: Soil dispensing mechanism via slurry
🢝 Rear portion: Precast concrete sections placement mechanism

Hauling of Muck
• Mucking and Hauling refers to the operation of loading and removing
excavated material and dumping it to predetermined sites. Removal of
muck is started as soon as it is safe for both men and machines. The
time taken in mucking represents as much as one third of total cycle
time, so work should be planned to make the operation as fast and
continous as possible.
Mucking
• The operation of loading the rock earth or eany other excavated material
for removal for the tunnel is referred as Mucking. The various methods
for Mucking are

Lining and Grouting of tunnels
• Lining methods, which are the permanent support methods for the tunnel, play
the main role for keeping tunnel from collapse and provide safe operations. There
are different lining methods for tunnels. Selecting the efficient lining method
should be in the context of the whole methods used for tunnel construction to
achieve a harmonised tunnel construction system.Technical and nontechnical
factors control the selection of the efficient tunnel lining methods.

Technical functions
1. Tunnel function: Tunnel function is an important factor in deciding what will be
the tunnel lining. Tunnels for water transfer need smooth lining. Railway tunnels
need strong lining under the rails to support the high load generated by the trains.
During the design of the lining matrix the aim was to determine which type of lining
is more efficient for tunnel function. Tunnel functions are divided into water
conveyance tunnels, road tunnels, railway tunnels, storage tunnels and defense
tunnels.
2. Tunnel cross sectional profile: Tunnel profile affects the constructibility of a
tunnel lining. The time needed to construct the final lining is different depending on
tunnel profile and lining type. The objective of this factor is to determine efficient
lining methods depending on tunnel profile.

3. Groundwater conditions:
Leakage of groundwater into the finished underground structure severely affects
the quality of the space and is very difficult to correct. Groundwater sealing is a
function of the water insulation system as well as of the lining system. In case of
electric installations inside the tunnel, water sealing is very important. Sometimes
two layers of lining are used to provide satisfactory protection against water
inflow. Groundwater flow into the tunnel is directly relational to the groundwater
pressure around the tunnel. Groundwater pressure on the lining depends on
groundwater table height and relative permeability of the ground. Groundwater
inflow rate represents groundwater pressure and ground permeability,
the amount of groundwater that the lining method will resist should be taken into
consideration during selecting the lining method.

4 Ground conditions: Ground properties have a great influence on the selection of
the tunnel lining. Selection of a lining method should be done carefully and a high
degree of safety must be always in tunnel designer’s mind.
Purpose of Lining
The permanent lining in tunnels serves the following purposes:
Saves the rock from air slake.
Saves or reduces the cost of removing loose pieces fallen down and unwatering by
holding the pieces and water.
For water tunnels, smoother surface by lining transports more water without
turbulence of flow,.
Adds to the structural strength in soft places.
Gives correct shape to the tunnel.
Withstands soil pressure when driven in soft soil..

Types of Lining
1. Timber Lining: Timber is used as a temporary expident and is replaced by cement
concrete or other type of lining. It is cheap and rapid in construction. Timber gives
groaning sound before tending to collapse.The disadvantage of timber lining is that it
decays and there is a danger of burning and fire hazards.
2. Cast Steel Lining: This type of lining is used as a primary lining for shields. It costs
very high so its use is limited.
3. Pressed steel liner plates: This type of plate is occsionally used for the primary
lining of small shield driven tunnels. The size of plates is approx. 40cmsx90cms with
5cm wide flange. It is not well suited to withstand horizontal pressures. Sometimes
corrosion may effect steel linear plates
4. Brick Lining: This type of lining is not in use now a days. it is used mostly in sewers
due to its acid resistant properties. Bricks used in lining should be well burnt, laid
longitudinally in quality mortar.
5. Stone masonary lining: This type of lining becomes very heavy, however it is used in
side walls occasionally. Rubble stone masonary is usually employed except at
entrances. Where masonary is exposed to view, ashlar masonary is used.

6. Concrete and R.C.C. Lining : Concrete lining is very common npow a days for tunnels
both in hard rock and soft rock. Thickness of the concrete lining depends upon the
1. Conditions of the ground
2. Size and shape of the cross section
3. Amount of horizontal and vertical pressures.
4. Construction conditions
5. Internal Pressures in case of water tunnels.
Advantages
1. it is water tight.
2. It provides a smooth surface.
3. Thickness can be controlled easily and it can be used to form an unbroken ring right
round forming a shell.

Alignment of
tunnels
Grades for Tunnels
Alignment of a tunnel, both horizontal and vertical, generally consists
of straight lines connected by curves. Minimum grades are
established to ensure adequate drainage. Maximum grades depend
on the purpose of the tunnel. Construction of a tunnel in the upgrade
direction is preferred whenever possible, since this permits water to
drain away from the face under construction.

Ventilation system
Tunnels will be required to be ventilated to dilute or remove
contaminants, control temperature, improve visibility and to
control smoke and heated gases in the event of a fire in the
tunnel.
Requirements of a ventilating system
A tunnel ventilating system must fulfill the following
requirements:
1. Tthe fumes from blasting must be cleared quickly from the
working face so that work can be resumed after blsting without
delay.
2. It must prevent accumulation of dangerous concentration of
fumes anywhere along the length og tunnel.
3. Ventilating system must provide an atmosphere at the face
in which the men can work comfortably and efficiently.
4. It should reduce to safe limits the dust produced by the
tunnel operations.

Voloume of Air required
Amount of air required per man depends
upon the local conditions such as:
• length of heading
• Size of the tunnel
• Amount of explosive used and its type
• Frequency of blasting
• Temperature and humidity.The Quantity
of ventilation required in a working area
is to base it on a minimum of 8.4
cub.meters of fresh air per man per
minute.

Types of Ventilation
1. Natural Ventilation
Naturally ventilated tunnels rely primarily on atmospheric conditions to maintain
airflow and a satisfactory environment in the tunnel. Naturally ventilated tunnels over
1,000 feet (305 meters) long require emergency mechanical ventilation to extract
smoke and hot gases generated during a fire Tunnels with lengths between 800 and
1,000 feet (240 and 305 meters) will require the performance of an engineering
analysis to determine the need for emergency ventilation. Because of the
uncertainties of natural ventilation, especially the effect of adverse meteorological and
operating conditions, reliance on natural ventilation, to maintain carbon monoxide
(CO) levels, for tunnels over 800 ft (240 m) long should be thoroughly evaluated. If the
natural ventilation is demonstrated to be inadequate, the installation of a mechanical
system with fans should be considered for normal operations. Smoke from a fire in a
tunnel with only natural ventilation moves up the grade driven primarily by the
buoyant effect of the hot smoke and gases. The steeper the grade the faster the
smoke will move thus restricting the ability of motorists trapped between the incident
and the portal at the higher elevation to evacuate the tunnel safely.

2. Mechanical Ventilation
A tunnel that is sufficiently long, has heavy traffic flow, or experiences
adverse atmospheric conditions requires mechanical ventilation with
fans. Mechanical ventilation layouts in road tunnels are either of the
longitudinal or transverse type.
Longitudinal Ventilation
This type of ventilation introduces or removes air from the tunnel at
a limited number of points, thus creating a longitudinal flow of air
along the roadway. Ventilation is either by injection, or by jet
fans. Injection. Air injected at one end of the tunnel mixes with air
brought in by the piston effect of the incoming traffic. This type of
ventilation is most effective where traffic is unidirectional. The air
speed remains uniform throughout the tunnel, and the concentration
of contaminants increases from zero at the entrance to a maximum
at the exit. Injection longitudinal ventilation with the supply at a
limited number of locations in the tunnel is economical because it
requires the least number of fans, places the least operating burden
on these fans, and requires no distribution air ducts.

• Longitudinal ventilation is achieved with specially designed axial fans (jet fans)
mounted at the tunnel ceiling. Such a system eliminates the spaces needed to house
ventilation fans in a separate structure or ventilation building. The disadvantages of
longitudinal systems, such as excessive air speed in the roadway and smoke being
drawn the entire length of the roadway during an emergency, become apparent.
• A longitudinal ventilation system must generate sufficient longitudinal air velocity to
prevent the backlayering of smoke. Backlayering is the movement of smoke and hot
gases contrary to the direction of the ventilation airflow in the tunnel roadway. The
air velocity necessary to prevent backlayering of smoke over the stalled motor
vehicles is the minimum velocity needed for smoke control in a longitudinal
ventilation system and is known as the critical velocity.

Transverse Ventilation
Transverse ventilation includes systems that distribute supply air and collect exhaust
air uniformly along the length of the tunnel. There are several such systems including
the full transverse system which includes both supply and exhaust air uniformly
distributed and collected.
The semi- or partial transverse systems incorporate only one, either supply or
exhaust air. Semi transverse ventilation can be configured as either a supply ystem or
an exhaust system. Semi transverse ventilation is normally used in tunnels up to about
7,000 feet (2,000 meters);beyond that length the tunnel air elocity speed near the
portals may become excessive.
Supply semi transverse ventilation applied to a tunnel with bi-directional traffic
produces a uniform level of contaminants throughout the tunnel because the air and
the vehicle exhaust gases enter the roadway area at the same uniform rate. In a
tunnel with unidirectional traffic, additional airflow is generated in the roadway by the
movement of the vehicles, thus reducing the contaminant level in portions of the
tunnel

Lightning of tunnels
In tunnelling operation activities cannot be carried out effectively if the light conditions are not
favorable. A light intensity of 260 lumens per sq. m in the working area is considerd satisfactory fpr
proper efficiency
Lightning of Tunnels during Service
Rapid-transit tunnels are lighted sufficiently to make obstructions on tracks visible and to facilitate
maintenance work. The lights are installed and/ or shielded to prevent glare in the motorman’s eyes.
Luminaires are installed in tunnels for emergency use. For highway tunnels, the most troublesome
lighting condition is the transition from bright light in the approach to the tunnel, the entrance
(threshold zone) luminance, to the luminance in the interior. Daylight penetration through the portal
into the threshold zone may assist the transition. In addition to the threshold zone, two or three
transition zones gradually reduce the luminance to that of the interior. The length of each of these
zones should be approximately one safe-stopping sight-distance (SSSD) at design speed. Reduction
between zones should not exceed 3:1.At night, a pavement luminance of 2–5 cd/m2 minimum is
recommended for the entire length of the tunnel. The approach and exit roadways should have a
luminance level of no less than one third the tunnel interior level for a distance of a SSSD.

There are four viable types of light sources used in
tunnels:
1. Fluorescent Lamps
2. Low-pressure sodium (LPS)
3. High-pressure sodium (HPS)
4. Metal halide (MH)
Florescent lamps frequently provide the lower
illumination levels, combined with LPS at threshold and
transition zones. Lower wattage LPS sources are also
used in interior zones. HPS and MH lamps come in a
wide selection of sizes, better lamp life, compact size
and are easily optically controlled.

spacing of Lights
The spacing of light along the tunnel depends upon several factors including:
1. Tunnel Dimension: Small tunnel requires less height.
2. Sie of light source: Fewer bulb of greater wattage will be required.
3. Rock conditions: In light coloured rock such as lime stone lesser number oif lights
may be required as compared with a dark coloured rock like granite.

Safety Measures
General Safety Measures
• Accidents and hazards in tunneling occur due to many reasons, during the
construction including the following:
Causes of Accidents
• Limited working space
• Wet and slippery footings
• Inadequate lightning
• Unseen weakness in the rock
• handling of explosives
• Loading and hauling of muck
• Operationa and movement of trains
• Hoisting operation
• Working of machines above ground etc.

Preventive Measures
• Some of the preventive measures involved in various operations of tunnelling are
listed below:
• Most of the severe accidents occur due to rock falls. Proper design of timbers and
supports, frequent inspection of walls and roofs, prevents accidents due to rock falls.
• Defective timbering should be avoided and occasionally it should be checked that it
is not under undue stress.
• Tools and equipment should be kept in best condition as falling or breakdown of
equipment may result in accident.
• Debris and refuse should be kept clean, both on surface and underground for safety
and efficient operations.
• Pipes, rails and other material should not obstruct the movement and should be
brought to the site as needed. Tunnel should be kept clean.

• Provide extra light where essential material is stored.
• Footings should not be slippery and hazardous. Good walkways of plank or muck
should be provided and well maintained.
• Water should not be allowed to stand in pools on the floor as this obscures walking
conditions. This is prevented by proper drainage and ditching.
• Many accidents are due to poor lightning and so all the job should be kept well
lighted.
• All light and power line should be properly installed and all connections should be
well insulated.
• Cars carrying pipes, rails, steel and timber must be properly loaded. Overloading
should be avoided as loads projecting over to the sides are dangerous to man
working in tunnel.
• Shaft should be equipped with switches and devices to indicate when cage
approaches top or bottom limits.
• Automatic brakes in case of power failures and overspeed are essential for safe hoist
operations.

• Fire protection must be provided for all places. Extinguishers and fire hydrants are
very essential.
• Medical facilities and telephone communication should be provided between inside
and outside the chamber.
• Design of bulkhead and lining should be capable of resisting the internal pressure
talking into considerations the bending moment imposed on the lining by deflection
of bulkhead under pressure.
• Extreme care must be taken in compressed air tunnels to prevent fire. No SMOKING
is a positive requirement.
• Unauthorized persons should be kept away. Authorise visitors should be equipped
with safety hats and accompanied by the guide.

Tunnel Engineering.pptx

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Tunnel Engineering.pptx