1. Transportation Engineering Vol. II
Volume II
C Venkatramaiah
Transportation Engineering Vol. II

2. Part V Tunnel Engineering

3. Chapter 27: General Considerations in Tunnelling
Tunnel: A horizontal passage through an obstacle such as hill or through underground earth between two points on either side to take the route forward in a relatively short distance.
A tunnel can be used for a roadway, railway, or for carrying water for various purposes such as drinking, hydroelectric generation, drainage, irrigation, navigation, or for sewerage.
Alternatives for a tunnel
Open cut (up to a certain depth)
Detour around the obstacle (involves greater route length)
Advantages of a tunnel
Least interference to traffic above during construction
Less cost for land acquisition
Secure against bombing in times of war
Cheapest means to carrying water through long distances.
Tunnel Engineering

4. Slow progress in construction
Disadvantages
High initial cost
Slow progress in construction
Need for specialised equipment and skilled supervision
Need for illumination both during and after construction
Historical aspects of tunnelling:
Very old art practised by Egyptians around 4000 years ago. Tunnels were driven in France during the 17 th century C.E. for canals. Tunnels for traffic were driven in England and France later.
Modern tunnels of length 50 km or more have been possible with the advent of techniques such as shield tunnelling and equipment like Tunnel Boring Machines.
Tunnel Engineering

5. Size and shape of a tunnel Common shapes are:
(b) Horse-shoe section
(c) Oval section (major axis vertical)
(a) D-section
(d) Circular section
(e) Oval section
(major axis horizontal)
(f) Rectangular section
Tunnel Engineering

6. For highway tunnels, size depends on the number of traffic lanes.
Size of a tunnel
For highway tunnels, size depends on the number of traffic lanes.
For railway tunnels, gauge and number of tracks are the criteria
For tunnels needed for carrying water/sewage, the size depends upon the capacity required.
Tunnels for vehicular traffic
Railway tunnel for single track
Railway tunnel for double track
Highway tunnel
Tunnel Engineering

7. Tunnel approaches and portals
These are open cuts at either end, leading to the tunnel proper. The tunnel entrance (or exit) is called the 'portal'.
The approach is relatively short for steep slopes and long for flat slopes of the hill. A portal should be massive and aesthetic. It is supported by a retaining walls with wing walls.
Twin tunnels
More advantages than a single large-sized tunnel, especially for traffic tunnels.
Parallel tunnels are similar, but at much larger distance apart (15 m)
Tunnel approaches and portals
Twin tunnels
Tunnel Engineering

8. Classification of tunnels The criteria are:
(a) Purpose – Traffic tunnels and those for other purpose.
(b) Nature of material met with during construction –Rock and soft soil
(c) Alignment – short tunnels and spiral tunnels (in the form of loops)
Stability of tunnels
Tunnels derive their stability through
Bridge action/Arch action (stressed transmitted via the ends to the ground)
Pressure relief phenomenon (The residual stress is released, when the confinement of the rock is removed during excavation.)
Tunnel Engineering

9. Tunnels in India and abroad
Earliest tunnels were for the Railway-e.g., Parsik tunnel in Maharashtra. Karbude tunnel in Maharashtra is 6.50 km long. The oldest highway tunnel is the Jawahar tunnel in Jammu and Kashmir (2.5 km long). Rohtang tunnel in Himachal Pradesh is 8.80 km long. Delhi Metro Railway Tunnel is 6.50 km long.
Long road tunnels in the Alps in France and Switzerland are Montblanc and St. Gotthard tunnels (About 12 km and 17 km, respectively).
Channel tunnel under the England channel between England and France is 50.5 km long. Seikan tunnel of the Japan Railways is 54 km long, built under the Pacific Ocean.
Tunnel Engineering

10. Chapter 28: Alignment and Surveying of Tunnels
Investigations for tunnel construction during planning
These are:
(i) Soil exploration – engineering properties of the soils met with.
(ii) Geological conditions of the strata-defects in rocks and petrology o the rocks.
(iii) Atmospheric conditions – Temperature, pressure and humidity.
(iv) Hydrological particulars at the site.
Investigations during construction of Tunnel Heading
Excavation of a part of the tunnel cross-section for a small length; it may be at the top, bottom, or the side of the proposed cross-section.
Valuable information can be obtained by the driving characteristics and the nature of the material met with.
Drift: A part of the tunnel cross-section, for the entire length of the tunnel, is excavated. This is done only for short tunnels. (Size of drift 3 to 5 sq. m.) Data about the nature of the strata is obtained for the entire length of the tunnel.
Tunnel Engineering

11. (c) Transfer of surface survey to underground
Alignment of tunnels
Alignment should be preferably straight, but in exceptional cases or because of errors in alignment, it can be a flat curve. Tunnels should not be located in environmentally protected zones.
Gradients in tunnels
Minimum longitudinal gradient to 0.50%. For short tunnels, gradient is given on to one side only; for long tunnels, it is given on to either side from the middle.
Surveying for tunnels
Marking the centre line of a tunnel underground comprises the following:
(a) Surface Survey
(b) Surface alignment
(c) Transfer of surface survey to underground
(d) Levelling underground in the tunnel.
Tunnel Engineering

12. Surface survey
Contour survey by means of a tacheometer is conducted for at least 2 km on either side of the proposed centre line and plotted to a small scale-1:20, 000 say.(contour interval can be 5 m).
The final alignment is selected based on a study of the geological conditions, and marked on such a plan. A mining transit may be used.
Surface alignment
The centre line of the tunnel is set out on the surface accurately, from end to end. If there is a single peak in the middle, from which both ends are visible, the method of 'balancing-in' is adopted repeatedly to fix the intermediate prints until the entire length is covered.
Tunnel Engineering

13. Transfer of surface survey to underground
The exact length of the tunnel is obtained by direct measurement such as the 'base line' for triangulation, or buy indirect methods such as traversing and triangulation.
Transfer of surface survey to underground
This is a difficult task, requiring skill and care. This is done through vertical shafts, excavated at regular intervals such as 500 m, and at closer intervals for short tunnels.
Direct measurement of the length of tunnel
Surface alignments of a tunnel
Tunnel Engineering

14. Wires and heavy plumb-bobs kept in pails of oil (to damp the oscillations of the wires) are used. Prolonging the centre line underground is done by using s precise theodolite in short stretches of 10 m. The Weisbach triangle is a popular technique used for this purpose.
White card between wires
Weisbach triangle
Transfer of alignment from surface to underground
Tunnel Engineering

15. It may be shown that  and  are related as below:
Levelling underground in the tunnel
This is accomplished through deep shafts, using steel band or rod.
For deep shafts, vertical measurements are transformed into horizontal measurements.
Illuminated signals are necessary for underground sights.
A high degree of precision is necessary in tunnel surveying; the permissible error in alignment for railway tunnels is as small as 25 mm. Error in levels is as low as 50 mm.
Transferring levels through deep shafts
Tunnel Engineering

16. Additional Working Faces
These may be obtained by driving (a) shafts (b) pilot tunnels
Shafts:
A 'shaft' is a vertical bore on the centre-line of a tunnel or on a line parallel, but close to it. Shafts are sunk from the ground surface down to the invert of the tunnel. Shafts serve multifarious functions in tunnelling; thus they form an important part of tunnel construction and maintenance.
For side shafts, a transverse passage called an 'adit' has to be bored to connect the shaft to the tunnel.
Size: 3 m  4 m to 6m.
Shape of section: depends upon the depth of the tunnel, intended uses, and nature of difficulties encountered during construction.
Classification of shafts:
(i) Temporary (ii) Working (iii) Permanent
Tunnel Engineering

17. Temporary shafts: 2 m square – to ascertain the nature of the strata.
Working shafts: Used to carry materials, augmenting ventilation needs, siding in alignment and transfer of levels.
Permanent shafts: Left permanently, even after the completion of construction. Usually, a circular section-2.5 m to 4.5 m diameter is used.
Sinking of shafts:
Sinking shafts through rock involves drilling, blasting and mucking, as in the case of tunnelling through rock.
Sinking shafts through soft soil may be by the 'drop shaft' method or by 'Underpinning' method. Necessary timbering is used.
Tunnel Engineering

18. Pilot tunnels
A 'pilot tunnel' is a parallel tunnel close to the main tunnel, but of smaller size, Cross-cut connections are provided between the pilot tunnel and the main tunnel. Apart from facilitating quick progress through additional faces, there are other uses as in the case of shafts.
Pilot tunnel system
Supporting the
shaft from top
Supporting the shaft from
bottom (by means of an arch)
Tunnel Engineering

19. Chapter 29: Tunnelling in Rock
Essential features of tunnelling in rock
(1) Usually, no timbering is required.
(2) Specialised machinery, and high –power drilling equipment is required.
(3) Power-requirement is high
(4) Expensive, but safe when compared to tunnelling in soft ground.
(5) Work can go on simultaneously at several faces' hence, progress can be at a fast pace.
General procedure of tunnelling in rock
The following are the steps:
(i) Construction of shafts
(ii) Excavation-drilling holes, charging with explosives and blasting.
(iii) Ventilation and dust removal
(iv) Mucking or removal of excavated material
(v) Temporary and permanent supports
(vi) Lining
Tunnel Engineering

20. Drilling Types of drills Mountings for drilling equipment
(i) Rotary drill-cutting by rotation under pressure.
(ii) Percussion drill-breaks rock by impact of blows, e.g., jack hammer drill (weighs 10 to 40 kg), and drifter drill (weighs 30 to 110 kg).
(iii) Abrasion drill-cutting by abrasion under pressure, e.g., shot drill-holes up to 750 mm diameter and depth of about 200 m.
Diamond drill-holes up to 300 mm diameter and depth of about 800 m.
Mountings for drilling equipment
Fixed mountings: Horizontal bar mounting (when width of tunnel is less than its height) column mounting (when the width is greater than height)
Movable mountings: Jumbo drill carriage on wheels (Continuous penetrator drills do not need changing of drill bits.)
Methods of drilling holes
(i) American method: a large number of deep holes, loaded fully with a small quantity of explosive.
Tunnel Engineering

21. (ii) English method: Shallow-and straight holes-suitable only for a narrow cutting.
(iii) Ring drilling method: Use in conjunction with centre-heading, to enlarge it to the full-size of the tunnel.
(iv) Bench drilling method: Jack hammers are used to drill vertical holes, which are about 10 mm apart, A bench is also drilled horizontally. ('Bench' is a horizontal portion on which workers an stand and drilling equipment can be placed.
Tunnel Engineering

22. RC Bow-string girder bridge
Types of cuts
Wedge cut-vent on V-cut (most commonly used type-on blasting, a wedge-shaped cone of rock gets removed).
RC Bow-string girder bridge
Tunnel Engineering

23. holes are made to meet near the axis of the tunnel.
(ii) Pyramid cut-holes slope both in the horizontal and vertical planes. Cut
holes are made to meet near the axis of the tunnel.
(iii) Bottom cut-or-draw-cut
Tunnel Engineering

24. Easers: Located around the cut holes and are blasted after them.
(iv) Top-cut and side cut-made in the top portion and side portion of the heading, respectively.
(v) Buster cut-or 'baby cut', used for deep holes. Their function is to relieve the burden of the main holes.
Based on function and sequence of firing drill holes can be classified as follows:
Cut holes: Located near the centre of tunnel section-main blast holes with maximum charge.
Easers: Located around the cut holes and are blasted after them.
Side holes or lifters: At the side and bottom-blasted after the erasers.
Top holes: Located near the top of the section-these are blasted last.
Tunnel Engineering

25. Blasting Economical depth of hole ... 1.5 m to 2.5 m
Drill bits. 20 to 25 mm hexagonal hollow steel, about 1 m long.
Modern tunnelling machines use water jet to help in excavation.
Blasting
Explosives used in rock blasting
Ammonia dynamics
Ammonia gelatin
Ammonium nitrate (94.5% NH4NO3 and 5.5% fuel oil)
Water gels (ammonium nitrate in aqueous solution)
Liquid oxygen (with suitable fuel like carbon or aluminium powder)
Firing: Initially, acetylene lamp/spitter fuse was used. Electrical detonators are now popular; permit successive firing of groups of holes using 'delay' mechanism.
Quantity of rock released on blasting:
Governing factors are:
(i) Rock characteristics
(ii) Explosive power of the charge
(iii) Number, depth, inclination and free faces of holes.
(iv) Stages of firing of holes
Tunnel Engineering

26. (v) Patterns of the drilled holes
Optimum depth of hole,
Here, W: Weight of charge
C: A coefficient which depends on strength of rock and
the depth of cut (an appropriate value has to be used).
Supports for a tunnel
The sides and roof of a tunnel need supports, especially when fully excavated or blasted. They may be stable only for some time due to bridge action. In order to prevent the caving in of the sides and roof due to stress concentration, supports are needed.
Temporary support systems:
Systems with timber/steel members.
'Square set' method or 'Cap and post' method (for small tunnels – about 2.5 m size)
Tunnel Engineering

27. Pavement supports Three-piers arch method (for medium-size tunnels)
Five –piece arch method
(for large tunnels)
Steel support systems consist of rolled steel sections
(I, H, T, or inverted T)
Pavement supports
Rock bolts: Pre-tensioned rock bolts are effective. 16 to 18 m diameter.
Bearing plates: Circular, triangular, rectangular, or pressed spherical plates in plan shape. Rock bolts may also be used in conjunction with bearing plates.
Tunnel Engineering

28. Methods of tunnelling in rock
(a) Top heading method
(i) Top-pilot –heading or drift method
(ii) Heading and bench method
(b) Centre heading method
(c) Full face method
(d) Pilot-tunnel method
Types of bearing plates
Rock bolt with bearing plate
Tunnel Engineering

29. Top heading – Top pilot heading (drift) method
2.5 m square top heading is first driven end to end of the tunnel, making it a drift. Then the sides are enlarged and later, the bottom portion is driven; this is multiple –drift approach.
Heading and bench method
A top heading of 2.5 m  2 m is first driven for a length of 3 to 4 m. This is later widened for full width and then the lower portion or the bench removed. This process is continued in stages.
Tunnel Engineering

30. Centre-heading method
New Austrian Tunnelling Method (NATM)
Most recent technique, popularly used for large tunnels.
Principles:
(i) Exploitation of original strength of the rock mass.
(ii) Protection by using shotcrete measurement.
(iii) Monitoring deformations during and after construction.
(iv) Additional supports are provided only when needed.
Mucking and hauling
'Mucking' is removal of debris from the blasting/excavation from the tunnel to outside of it.
'Hauling' the debris is done by various machines that use power.
Eimco loader and Conway shovel are two such machines.
A central drift of about 3 m square is first driven, and later enlarged to the required dimensions. Ring-drilling is adopted for this.
Tunnel Engineering

31. (c) Cherry picker – Overhead gantry girder with a track
A light railway, on which mucking cars of 2 to 4 Cum. capacity run, is convenient for haulage of the debris.
Mobile appliances have been devised to achieve quick replacement of a loaded car by an empty one:
California crossing
Grass hopper
(c) Cherry picker – Overhead gantry girder with a track
Tunnel Engineering

32. Precautions for tunnelling in rock Careful handling of explosives
Use of personal protection equipment
Timely location and removal of loose material
Availability of first-aid and medical facilities at the site.
Tunnel Engineering

33. Chapter 30: Tunnelling in Soft Soil
Classification of soft soils for tunnelling
(a) Ordinary soil, which is firm enough for the tunnel roof to stand unsupported for a short period; in fact, the sides can stand for a little longer period. Dry earth material and firm day are examples of this type.
(b) Loose or soft soil, which needs instant support for the roof. Soft clay is an example of this type.
(c) Treacherous soil or running ground, which needs instant support all around. Loose cohesionless soils, clay are examples of this type.
In the case of the second and third categories, excavation and timbering should go hand in hand.
Methods of tunnelling in soft soils
(1) Forepoling method
(2) Needle beam method
(3) Five-piece set method
Tunnel Engineering

34. American, English, Belgian, German and Austrian methods
(4) Classical methods:
American, English, Belgian, German and Austrian methods
(5) Army or case method
(6) Cut and cover method
Forepoling method: Useful in running ground
Slow and tedious method
The correct sequence of operations is to be strictly followed.
Small-sized tunnels for sewers or gas pipes are driven by this method.
The sequence of operations is shown in the figure shown:
Tunnel Engineering

35. The sequence of steps are shown in the figure:
Needle beam method
Useful in soils in which the tunnel roof can stand for some time without any support. 5 to 6 m long R.S. joists or timber beams are required, besides other timber boards and struts. A large number of jacks are required, thus causing obstructions in working space; however, this method is relatively economical.
The sequence of steps are shown in the figure:
Five-piece set method:
Useful in soft clay
A small drift of about 1.5 m  2 m is driven, supported by caps, and the heading is widened in the face using timbering.
Tunnel Engineering

36. The sequence of steps are
Classical Methods
American Method
Suitable for large-sized traffic tunnels.
Top drift is first driven and supported by lagging and two posts.
Sides of the drift are widened and supported on timbers and struts.
5 m long wall plates are introduced at springing, and supported by props.
Sides and benching are then cleared and completed.
English method
The sequence of steps are
Driving a central top heading about 5 m ahead
of the existing arch.
Supporting by crown bars, which are supported on posts in the front.
Widening of the heading, the sill piece being extended right across the tunnel.
Underpinning the extended sill on supports.
Tunnel Engineering

37. Belgian method Suitable for moderately firm soils. The steps are:
Driving a centre top heading (abcd), supporting by crown bars, posts and laggings.
Widening the heading sideways, supporting by additional crown bars and posts.
Fixing a horizontal brace at the springing.
Excavating a trench (MNOP) right down to grade level.
Clearing the alternating spaces between the shores and building the side masonry.
Removing the shoring and filling with masonry.
Finally, constructing the invert.
Tunnel Engineering

38. German method
Three drifts are employed – one at the crown and two at the bottom, close to
then side walls. The section is then widened to complete the section.
Austrian method
A Centre cut is made for the full height and then it is widened to the full face
to allow for the completion of short sections of the masonry. The New
Austrian Method (NATM) can also be employed for soft soils as for rock, since
the principles are applicable to both.
Army or Case method
Derived by US Army engineers-good for small tunnels at shallow-levels, say for underground sewers.
Tunnel Engineering

39. But it is useful only for short swallow tunnels. Cut and cover method
The advantage is that only simple timbers and trench jack are required.
But it is useful only for short swallow tunnels.
Cut and cover method
Shallow tunnels under city streets, underpasses, and end sections of tunnels through hills are built by this method.
A trench is excavated and a concrete tunnel is constructed within it. The completed tunnel is covered up and the surface reinstated; this is bottom-up construction.
In the top-down approach, the walls are constructed first, using bentonite slurry to stabilise the soil. the roof is constructed next, backfilled and the surface reinstated. Excavation and construction of the floors below the roof level then follow, using access from the ends.
Cast-in –place concrete is used; depth of invert does not exceed 12 m.
Excavation should be carried out without disturbing all utility and service installations. Timbering may be employed, if necessary.
Tunnel Engineering

40. Timbering methods
All the members should be in compression. Effective length should be reduced by means of bracings to prevent buckling.
Common types are:
One-piece set
Two-piece set
Three-piece set
Normal four-piece set
Four-piece set
Tunnel Engineering

41. Timbering use after construction of the tunnel
Special methods
(a) Liner plate method
(b) Shield method
Linear plate method:
Linear plates are corrugated thin
steel sheets with flanges to support
the tunnel section. Relatively expensive
when compared with timber. The sequence
of operations can be understood from the
figure shown:
Tunnel Engineering

42. Protective metallic shield is used for tunnelling in very soft soils.
Shield method
Protective metallic shield is used for tunnelling in very soft soils.
Tunnel-boring machine (TBM)
Consists of a large cylindrical metal shield and trailing support mechanisms. Used for the construction of large tunnels. In tunnelling by the shield method, compressed air pressure is used to counteract the pressure of water outside, so that the working chamber inside the shield is kept relatively dry, similar to a pneumatic caisson. The same principle is used for tunnelling in water-bearing soils.
Tunnel Engineering

43. Final finishing to the inner surface of the tunnel.
Tunnel lining
Final finishing to the inner surface of the tunnel.
Prevents possible failure of the roof or sides.
Materials for lining
(1) Masonry (brick or stone)
(2) Cement concrete (most common)
(3) Cast-iron or steel
(4) Timber (low cost is the advantage but is not preferred for important tunnels.)
In soft soils, it is preferable to provide lining for the roof, the sides, as also for the invert.
Pressure grouting/guniting is used for thin lining jobs.
Thickness of lining-at east of tunnel diameter.
Tunnel Engineering

44. Precautions in tunnelling through soft soils
(1) Stability of working platform should be ensured.
(2) Equipment should be maintained properly.
(3) Freshly excavated surfaces should be immediately supported.
(4) Proper ventilation and lighting should be provided.
(5) Protective year-clothing, helmet, gloves and goggles should be provided to the workforce.
(6) Fire protection measures should be in place.
(7) Communication facilities should be provided between different units.
Tunnel Engineering

45. Chapter 31: Ventilation, Lighting and Drainage of Tunnels
Ventilation of tunnels
Ventilation: Provision of adequate quantity of fresh air to workers and users of the tunnel for their safety and comfort.
The need for ventilation arises because of the accumulation of dust and foul gases during the various construction operations such as drilling, falling debris, and fumes from blasting. Mucking and hauling operations also cause air pollution in the tunnel. Even during operation of tunnels after construction, exhausts from vehicles in traffic tunnels need ventilation for safety and comfort.
Method of ventilation:
The methods may be classified as natural or artificial (mechanical) ventilation.
Natural ventilation: Possible in short tunnels of large diameter (say less than 300 m long and more than 3 m in diameter). The minimum volume of fresh air required per person per minute is about 6.5 cu.m; however, up to 15 cu. m is provided for a comfortable working ambience.
Tunnel Engineering

46. Mechanical ventilation: The following are the methods used:
(a) Exhausting foul air by means of exhaust fans and sending it through pipes/ducts provided near the working face. This creates a vacuum into which fresh air from outside flows in, naturally through the tunnel entrance o portal. This is called 'exhaust ' or 'Vacuum' process.
(b) Blowing fresh air into the tunnel by means of blowers; as this air flows towards the portal, dust and foul gases are pushed out. This is called 'blowing ' or 'plenum' process.
(c) A combination of exhausting and blowing is used alternately to exploit then advantages of both processes. The exhaust and blower systems are both operated by means of a reversible type of fan, which can act as an exhaust as well as a blower.
Tunnel Engineering

47. The following are the types of systems: (1) Longitudinal ventilation
The reversal of operations is accomplished by a value and duct arrangement shown in the figure:
Ventilation systems
The following are the types of systems:
(1) Longitudinal ventilation
(2) Transverse ventilation
(3) Semi-transverse ventilation
Tunnel Engineering

48. Longitudinal ventilation: This is the simplest; fresh air is introduced into the entry portal and exhaust air is expelled out of the exit portal. Ventilation fans are provided along the length of the tunnel.
This process is aided by moving vehicles through what is called the piston effect (similar to flow of air behind a piston moving in a cylinder).
Longitudinal ventilation Transverse ventilation
Transverse ventilation: This works on the same principle of dilution and removal as in longitudinal ventilation; however, the processes occur in the transverse direction of the tunnel. This requires two ducts along the length of the tunnel, one for supply of fresh air and the other for removal of polluted air in the transverse direction as shown in the figure.
Tunnel Engineering

49. Equipment required for ventilation
Semi-transverse ventilation: This is a combination of both longitudinal and transverse ventilation. Fresh air can be supplied along the tunnel continuously via a duct and exhausted out of the tunnel via the portals as shown in the figure. Alternatively, fresh air can be supplied from the portals and be continuously exhausted along the tunnel through a duct.
Equipment required for ventilation
Fans and blowers driven by electric power.
Ducts or pipes-may be flexible cloth
Fabric or wire-reinforced fabric.
Design of tunnel ventilation depends upon the requirements of air quality within the tunnel, ambient air quality criteria just outside the tunnel, and any other specific restrictions.
Tunnel Engineering

50. Dust control and prevention
The operations involved in tunnelling give rise to dust inside the tunnel leading to heavy air pollution. Continual breathing of silica dust leads to 'silicosis', a serious lung disease. Hence, dust control is mandatory.
The methods commonly used are:
(i) Wet drilling – directing water jets into drill holes while drilling.
(ii) Use of vacuum had-fitted around the drill bit for sucking dust and removed safely.
(iii) Use of respirators by workers-best personal practice.
Lighting in tunnels
Lighting is needed both during construction and later during operation and maintenance. Levels of illumination required during the day and during the night are different, For a given speed, the greater the difference between the level of the lighting outside and inside, the more would be the time needed for adaptation of the human eye, because of the 'black hole effect'.
Tunnel Engineering

51. The International commission on Illumination has made appropriate recommendations in tunnels.
A higher design speed requires an increased lighting requirement.
When one can see the other end of the tunnel from the entrance is a 'short tunnel'; otherwise, it is a 'long tunnel'. Even if the length is not much, if the tunnel cannot be seen from end to end, it is considered an 'optically long tunnel'.
Tunnel-related zones
Access zone – Threshold zone – Transition zone –
Interior zone – Exit zone – Parting zone
Lighting required depends upon the particular zone, during the day.
Glare should be minimised.
Emergency lighting should be available in the event of power failure.
Acetylene gas lamps have become obsolete.
Electric lights of appropriate design and wattage are used to provide the illumination required.
Tunnel Engineering

52. Drainage of tunnels
This is to deal with surface water from portals, groundwater infiltration through lining, wall-wash water, and fire-fighting water.
Groundwater leakage is a complex problem, difficult to predict correctly.
Empirical and semi-empirical formulae have been evolved for the rate of groundwater in flow (Q).
A few are given here:
Goodman:
Lei:
(3) Karlsrud:
In these equations,
k = Hydraulic conductivity
Ho = Initial head of water above the centre of tunnel.
h = head of water above the centre of tunnel
z = Distance to tunnel from the water source
r = radius of the tunnel.
Tunnel Engineering

53. Site Groundwater Rating (SGR)
This is a new concept for rating tunnel site from ground water hazard point of view, This is based on engineering, geological and hydrological properties.
Six ratings – No risk, low risk, moderate risk, risky, high risk, and critical, based on the SGR value: 0 to 100, 100–300, 300–500, 500–700, 700–1000, and greater than 1000, respectively.
Drainage structure components
(i) Weep holes in lining
(ii) Concealed conduits
(ii) Side drains and bottom central drain
(iv) Gulleys, channels and pipes
(v) Sumps and pumps
(vi) Control systems for storage separation and disposal of the effluent.
(vii) Covered drains under the floor/invert
(viii) Oil/water separators.
Tunnel Engineering

54. Classification of drainage in tunnels
(a) Drainage prior to the construction of tunnel
(b) Drainage during the construction of the tunnel
(c) Drainage during the operation of the tunnel.
The requirements and the drainage components used are somewhat different in reach case. Drainage is an important aspect for tunnels and has to be properly designed, and maintained during their service life.
Tunnel Engineering

55. Chapter 32: Operation and Maintenance of Tunnels
Operations and maintenance of tunnels is an important aspect of tunnelling to ensure that the tunnel serves the purpose for which it is constructed, during its entire service/design life.
Different organisations are concerned with the maintenance of road tunnels, railway tunnels, water supply and sewage tunnels, underways and subways, and so on.
Components and aspects needing maintenance
Ancillary civil engineering structures for shelter and maintenance.
Shafts and adits
Tunnel lining
Tunnel drainage
Ventilation and dust control
Tunnel lighting
Tunnel Engineering

56. Methods and maintenance of tunnels
PIARC (Permanent International Association of Road Congresses) have brought out a Road Tunnels Manual about 'Operation and Maintenance of Tunnels. (PIARC is also known as 'World Road Association')
Daily Management:
Activities to monitor traffic and ensuring efficient functioning of all the equipment needed during operation.
Training of the staff:
This is a multi-organisation task-the operator, traffic police, fire brigade, and other emergency services for safety in tunnels.
Continuous improvement of safety:
Includes all activities of study and planning, which aim at a continuous improvement of safety-emergency planning, feed back of experience of accidents, replacement of tunnel equipment, and so on.
Tunnel Engineering

57. Players in tunnel operation
Operational tasks
(i) Traffic surveillance and operation of tunnel equipment.
(ii) Technical patrolling inside the tunnel
(iii) Management of emergencies
(iv) Technical and administrative management.
Players in tunnel operation
(i) Tunnel operator
(ii) Operators of different parts of road network.
(iii) National and local administrative authorities
(iv) Public services such as fire and rescue services, traffic police and medical services.
(v) Sub-contractors, if any, for cleaning, maintenance, etc.
Organisation of operations
(i) Operating staff (including emergency rescue staff)
(ii) Technical staff
(iii) Administrative personnel
Tunnel Engineering

58. Operating costs Shafts and adits Lining Ventilation Lighting
A kilometre of tunnel is always costlier than a kilometre of road in an open area. This is because for an underground structure, several systems and equipment are deployed, which need continual maintenance.
Shafts and adits
Used for construction and for later maintenance operations-for storing equipment and moving workers.
Lining
Usually cement mortar/concrete. Lining thickness has to be restored by shotcreting or guniting, whichever is appropriate.
Ventilation
Ventilation equipment such as fans or blowers, or a combination of both, have to be maintained on a regular basis to ensure the safety and comfort of the tunnel users.
Lighting
The system of lights installed for night-lighting and day-lighting have to be periodically inspected, and defective lights have to be promptly with new ones. This is essential for the safety of tunnel users.
Tunnel Engineering

59. (a) Organisation for Economic Cooperation and Development (OECD)
Safety in tunnels
Guidelines and recommendations for safety in tunnels are based on the findings of a joint research project sponsored by-
(a) Organisation for Economic Cooperation and Development (OECD)
(b) PIARC's committee on Road Tunnels
(c) European Commission(by way of financial support).
Aims of the project
(i) To develop as a system of regulations for international use as a common reference.
(ii) To examine the risk assessment and decision processes in current use and develop tools to improve these processes.
(iii) To review risk reduction measures and to evaluate their effectiveness to improve safety in tunnel operation.
Tunnel Engineering

60. Treatment of hazardous goods through tunnels
Common lists or "groupings" of dangerous goods have been proposed, along with common regulations, which are easy to enforce and to be complied with. It would also facilitate international transport and improve trade.
The number of groupings of hazardous goods should be reasonably low for the system to be practicable.
The proposed grouping system is based on the assumption that there are three 'major hazards' possible in a tunnel, which may cause heavy casualties and possibly serious damage to the structure. The possible hazards are
Explosion
Release of toxic gas or volatile toxic liquid
Fire
Tunnel Engineering

61. The main consequences of these hazards are: 1. Large explosions
 Very large explosion (e.g., explosion of a full load of LPG in bulk, heated by a fire; Boiling Liquid Expanding Vapour Explosion –BLEVE – followed by a fireball, referred to as hot BLEVE).
 Large explosion, typically the explosion of a full load of non inflammable compressed gas in bulk heated by a fire (BLEVE with no fireball, referred to as cold BLEVE).
There is no possibility to mitigate the consequences in these cases.
2. Large toxic gas releases
 due to leakage from a tank containing toxic gas or a volatile toxic liquid. All the people in the tunnel will be killed. Only a party of the tunnel may be protected.
Large fires
 these may cause a few to several deaths and serious damage to the tunnel.
Tunnel Engineering

62. Quantitative Risk Assessment Model (QRAM)
Groupings
A to E, in the order of increasing restrictions, are given below:
A- All dangerous authorised on open roads
B- All loadings in A, except those which may lead to a very large explosion.
C- All loadings in B, except those which may lead to a large explosion.
D- All loadings in C, except those which may lead to a large fire.
E- No dangerous goods- most restrictive category.
Differentiated time regulations may be placed when mixed loadings of hazardous goods. When mixed loadings are there on the same vehicle, the first alphabetical loading is used for the whole loading.
Quantitative Risk Assessment Model (QRAM)
This is a unique tool, evolved by the expert committee, to assess the risk and quantify it under a given set of circumstances.
Scenarios representation of each grouping-A to E- in QRAM are tabulated.
Decisions Support Model (DSM)
A computerised tool has been developed, making it possible to arrive at an appropriate decision, based on QRAM.
Tunnel Engineering

63. Risk-reduction measures
Several measures can be implemented in tunnels which will reduce either the probability or the consequences of an incident in a tunnel.
These measures have also been tabulated by the committee, which are expected to be implemented by all concerned, An international Regulatory Framework is recommended to be formed under the aegis of the UN.
Tunnel Engineering