Document Sample
					                                                                            E-VISION 2009

                          UNDERGROUND TUNNEL AND
                            TUNNELING METHODS
                                          Rajkumar Chaulagain

Introduction                                                   Blasting      : applicable to medium and hard
Tunnels are artificial passage built underground to       3. Fixing temporary supports, as necessary.
facilitate transportation, storage or protection.         4. Removal of bladed/excavated material.
Tunnels have been built from time immemorial for          5. Dressing, fixing final supports, followed by final
various purposes. The earliest known tunnel was                operation of lining, wherever necessary.
constructed about 4000 years ago by Queen                 Where all condition are favorable, construction
Semiramis in ancient Babylon under the Euphrates          becomes relatively simple, but the history of
River to connect her palace and the temple of Jove.       tunneling shows how often unexpected physical
The tunnel was 1 Km long and was of section 3.6 x         conditions have made a project impossible as
4.5 m.                                                    originally conceived , and ultimately only achievable,
The principal function for which tunnels other than       after years of immense effect, by virtue of new
mining tunnels and military sappers tunnels , are
                                                          Factors related to tunneling function
build include :
                                                      The factors related to above fundamental operations
1.   Transportation                                   are mutually interdependent and are not separate for
    • People and goods : Pedestrian and cycle subway, decision making. Those are
         Railways and motors, Highways
    • Water: Canals, City supplies, Irrigation,       1) Situation for a tunnel may be through a mountain
         Hydroelectric power, Cooking water               or hill, or subaqueous, or urban.
    • Sewers                                          2) Ground may be anything from soft silt to hard
    • Cables and pipe services                            uniform rock covering a very wide range of
2. Storage and plant                                      behaviors in excavation; water may play an
                                                          important part. Any choice of ground implies
    • Car parks                                           changes in geometry, structural form and
    • Cavern storage of oil                               construction method
    • Underground power stations                      3) Dimension and geometry are those of the
    • Military stocks                                     finished tunnel: width, height, and length,
    • Disposal of radioactive waste                       together with levels and gradients and curves.
3. Protection of people                                   Specified limits may be very narrow or offer a
                                                          wide range of possibilities.
    • Shelters                                        4) Structural form may be circle, horseshoe,
    • Control posts                                       rectangle, or other shape incorporating cast-iron,
                                                          concrete, brick work, sprayed concrete etc, to
The fundamental operations of tunneling are:              carry the loads imposed. The nature of the
1. Survey                                                 ground and method of construction influence
2. Tunneling operations, apart from fixing the            strongly the structural form.
    alignment and the lining (which are           the 5) Construction methods range from boring by
    preliminary and final aspects of constructions of     drilling and blasting, or by tunneling machine, or
    a tunnel) comprises        these     intermediate     with or without a shield, to cut and cover in
    operations:                                           various sequences, and submerged prefabricated
    Excavation : applicable to soft soils                 tunnels. The choice of method is limited by the
    Picking       : applicable to medium soils and        ground condition, but also by available resources
    very sift rocks                                       in the widest sense.

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6) Equipment of the completed tunnel include such           ii. Tunneling with Liner plates
   features as roadway or rail track, lighting,           This is generally used for either forming drifts or
   ventilation, decorative and functional finishes,       headings on medium soft ground. It can also be
   control systems.                                       adopted for small cross-section drifts in running
                                                          ground, combined with compressed air.
All of these things are taken fully into account in the
                                                            iii. Needle Beam Method
planning and design of the project. It is usually most
                                                          This method is modification of the liner plate
unsatisfactory and inefficient to make sustainable
                                                          method. It is applicable wherever the roof can stand
addition or alterations at a later stage, except where
                                                          for a few minutes and the sides for an hour or two as
proper provision has been made in the original
                                                          in stiff clay. The full section of the tunnel is broken
                                                          up into successive portion.
Tunneling Methods                                           iv. Flying Arch Method
The adoption of any one of a number of possible           The flying arch method is similar to the needle beam
methods for tunneling depends on the nature of the        method except that no beam is used for supporting
soil profile. Soils can be grouped under soft strata or   the liner plates. As the top heading is driven, the liner
rock. Soft strata may be cohesive soil (clay), or         plates of the arch are supported by trench jacks
granular soil or mix. Tunneling through soft strata is    resting on the bench itself.
done by using one of the traditional methods of                v. Shield Tunneling
diving, i.e., excavation by digging or with a tunneling   The shield tunneling method is used in loose, non-cohesive
machine. The machine is generally used in very soft       or soft ground. It is mostly circulars in shape. It can be
layer and clay and prevails in subway construction.       driven either in free air is under compressed air. The former
Wherever seepage flow is heavy, the operation has to      method is used when the depth of the tunnel is shallow
be supplemented by use of compressed air.                 and/or there is not much likelihood of ingress of water, as
Occasionally some drilling and blasting is also done,     in clayey soils. The advantage of the shield tunnel is that it
                                                          permits excavation of soil and erection of primary lining
especially in the case of mix soft rock and in laterite
                                                          under safe conditions. It also provides better control of
types of soil.                                            ground settlement from above as well as on the sides.
A number of methods have been developed for
tunneling by machine and the choice will generally
depend on the type of soil of structure etc.              2.    Tunneling by tunnel boring machines (TBMs)
1. Traditional Methods
   a. Sequencing                                          These associate back-up systems which can be used to
The traditional methods of sequencing operation to        highly automate the entire tunneling process. There are a
achieve full profile may be classified as follows:        variety of TBMs that can operate in a variety of conditions,
    i. Full face method                                   from hard rock to soft water-bearing ground. Some types of
   ii. Top heading and benching method                    TBMs, bentonite slurry and earth-pressure balance
  iii. Bottom heading and stopping method                 machines, have pressurized compartments at the front end,
  iv. Drift method, sub classified method into wall       allowing them to be used in difficult conditions below the
        plate drift method, side drift method and         water table. This pressurizes the ground ahead of the TBM
        multiple drift method.                            cutter head to balance the water pressure. The
The first three methods are generally used for rocks
(aided by blasting) and medium type soils, while the      operators work in normal air pressure behind the
last (iv) is used for soft rocks and disintegrated rock   pressurized compartment, but may occasionally have to
(requiring ground support).                               enter that compartment to renew or repair the cutters. This
   b. Excavation and advancing                            requires special precautions, such as local ground treatment
                                                          or halting the TBM at a position free from water.
These are the methods of making tunnel with simple
                                                          Despite these difficulties, TBMs are now preferred to the
   i. Fore poling Method                                  older method of tunneling in compressed air, with an air
The fore poling method is the most commonly used          lock/decompression chamber some way back from the
in gravelly cohesion less soil, particularly in running   TBM, which required operators to work in high pressure
ground for small tunnels, as well as driving headings     and go through decompression procedures at the end of
in some other cases. Fore poles are timber planks         their shifts, much like divers. Until recently the largest
with wedged ends which can be driven through the          TBM built was used to bore the Green Heart Tunnel

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(Dutch: Tunnel Groene Hart) as part of the HSL-Zuid in the     specially made pipes through the ground behind a tunnel
Netherlands. It had a diameter of 14.87 m.                     boring machine or shield. This technique is commonly used
                                                               to create tunnels under existing structures, such as roads or
Pipe Jacking, also known as pipe-jacking, is a method of       railways.
tunnel construction where hydraulic jacks are used to push

S.N.         Name of Hydropower            Length (m)            Shape or Cross section (m or m2)

1            Kaligandaki-A                 5 925                 Dia. 7.4

2            Marsyandi                     7199                  Dia. 6.4

3            Kulekhani-I                   6233                  Dia. 2.3

4            Kulekhani-II                  5847.8                Dia. 2.5

5            Modikhola                     2071

6            Puwakhola                     192                   D-shape 2.3*2.3

7            Seti                          1555

8            Middle Marsyandi              5210                  Dia. 5.4

9            Chameliya *                   4418.3 (4 total)      3 D-shape & 1 Horseshoe shape

10           Kulekhani-III*                6924.7 (5 total)      O, D & Horseshoe shape

11           Upper Tamakoshi *             9730 (2 total)        29 &7.1

13           Bhotekoshi                    3301                  D-shape(4*4)

14           Chilime                       3069.5                D-shape (3.5*3.75 & 3*3)

15           Indrawati                     3000                  D-shape(3.25*2.5)

16           Chakukhola                    958                   D-shape(1.8*2)

                                      Some hydropower tunnels of Nepal


•      Tunnels planning, design construction, vol.1, J.M.Megaw and J.V.Bartlett
•      Transportation tunnel, S. Ponnuswamy, D. Jhonson Victor
•      Nepal Electricity Authority, Generation, August, 2008, 6th issue
•      www.tunnelwikipedia, the free encyclopedia.htm
•      www.himalhydro.com.np

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