ijrar october 2018, volume 5, issue 4 -issn 2348 1269, p issn … · 2018. 10. 9. · ©e2018 ijrar...

© 2018 IJRAR October 2018, Volume 5, Issue 4 www.ijrar.org (E-ISSN 2348-1269, P- ISSN 2349-5138)

IJRAR1904043 International Journal of Research and Analytical Reviews (IJRAR) www.ijrar.org 392

STRATAGIES AND CONSIDERATIONS FOR

CONSTRUCTION OF IMMERSEDTUNNEL IN

INDIA (INDIA GATE-ELEPHANT CAVES)-A

12KM IMMERSED TUNNEL 1B. Aravind Sai Atchyuth, 2S. Aishwariya

1Student, Department of Civil Engineering, GMR Institute of Technology, Rajam, Andhra Pradesh, India. 1Assistant Professor, Department of Civil Engineering, GMR Institute of Technology, Rajam, Andhra Pradesh, India.

________________________________________________________________________________________________________

Abstract— Immersed tunnels are a new type of transport structure. It is different from the long span bridges and bored tunnels

and has an advantage in crossing long, large and deep water areas. They are commonly used for road and rail crossings of rivers,

and sea channels/harbors. Immersed tubes are often used in conjunction with other forms of tunnel at their end, which is usually

necessary to continue the tunnel from near the sea shore to the entrance at the land surface. This type of structural system is suited

for waterway crossings in seismicity zones. It is less risky than bored tunnel. Despite of many advantages it has disadvantages on

other side such as impact on sea bed. The construction methods mainly involve wave load determination, vortex-induced

vibration, immigration and reduction of accidental load and situation, durability, innovational construction method, risk

identification and control etc. They are constructed in Binocular and Rectangular section. To check the immersed tunnels

responsibility for seismic loadings a response spectrum analyses was carried out. Immersed tunnels in India are necessary in the

modern world as it was a significance of development. A 12 Km immersed tunnels was planned to Elephant caves from two ends

of Mumbai city. One is from India gate and the other from north end of Mumbai. Several factors which are to be considered for

the construction such as Seismicity action, Marine environment in the area of construction, Geotechnical conditions, Settlement

issues, Settlement due to offshore conditions (uplift and horizontal problems), Action of waves etc., All the key problems were

discussed and methodology required for solving a particular problem so that to provide the better design for tunnel construction.

Key words— seismicity zones, vortex-induced vibration, durability, Immersed tunnels.

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1. INTRODUCTION

Traditionally long span bridges are applied for river crossings and often in delta areas and in soft soil conditions. As an alternative

to a bridge, in countries like the US, Japan and the Netherlands many of these fixed links have been constructed as a tunnel with

the immersed tunnel technique. In these countries this technique is very common. However, in the recent years there is a scope for

this technique in other countries. Recent tunnel projects have shown that immersed tunnels are feasible and competitive to a long

span bridge under more challenging circumstances. Immersed tube tunnel is an alternative to bridges and bored tunnels for the

crossing of harbors/rivers. Immersed tube tunnel units of length of about 100m long, usually forming a length of complete tunnel

cross-section with both ends temporarily sealed by a bulkhead are fabricated in a dry dock. The sealed units are floated and towed

to the tunnel location and lowered into a pre-dredged trench in the sea or river bed. Immersed tunnels have been constructed

successfully in water depths up to 58 m below sea level, in very poor soil conditions, with increasing lengths, increasing design

lives and in offshore conditions. Natural boundaries and obstructions such as sea straits, large estuaries and in land water ways

can increase costs and time for transportation. The options are either a bored tunnel or a bridge to cross these straits. Immersed

tunnels can provide economic, high quality and competitive solutions to cross water ways. Especially when crossing water ways

in an urban environment or when high air clearance of deep navigation channels is required, like in main ports. Several

innovations have been taken place for the development of immersed tunnels. The Fehmernbelt Link, the link between Denmark

and Germany comprising an immersed tunnel of almost 19 km which is the largest tunnel. In fact, the immersed tunnel can be

competitive to a long span bridge in many fixed link projects. The history of immersed tunnels for transportation started in 1910

with the construction of a two track tunnel between the USA and Canada. The two methods followed for the construction of

immersed tunnels are based on the selection of the construction material i.e., steel in the USA and concrete in Europe.

2. NECESSITY OF IMMERSED TUNNEL IN INDIA

India is a developing country in the present day world in all the fields; it should also a bit advance in transportation sector.

Immersed tunnels are an innovative motive structure in the present world.it is used to cross long lakes and major ports in a short

time. Since elephant caves is among the famous tourist places in India immersed tunnel will help in increase the tourist attraction

towards it. Since there is only water way to reach it, it is necessary to have a road way to reach the caves. A 12km immersed

tunnel is to be constructed in Arabian Sea to reach the elephant caves from two parts of Mumbai.

3. FACTORS TO BE CONSIDERED AND REMEDIAL MEASURES FOR THE CONSTRUCTION OF IMMERSED

TUNNEL IN THE ARABIAN SEA:

I) Seismicity action: Immersed tunnels are mainly constructed in the areas having seismicity action. So to assess the seismicity

action in the region of Arabian Sea several studies were conducted and research was done by Pakistan meteorological department.

They have collected the data between1905-2002 regarding seismicity actions in the region of Arabian Sea including Mumbai and

assessed the results. The character of seismic activity in the Arabian Sea is described by frequency magnitude relationship

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according to Gutenberg and Richter scales. From the data record of Arabian Sea, it is found that, there were five earthquakes

having body magnitude (Mb) greater than and equal to 6.0 since 1905. The ever-big earthquake Mag 8.3 Richter scale was

occurred on 27 Nov 1945, which created Tsunami. The following figure gives the keen data of seismicity actions from 1932-

2002.Since the highest earth quake is above the magnitude of 8, the bridges constructed in this region cannot bear such high

magnitude and there may be chance of failure of structure. Experimentally it is proved that the immersed tunnels can bear the

magnitude of 12 which was done during construction of Istanbul immersed tunnel. So there would be no damage to the tunnel if

earth quake occurs in this region.

Fig.1 Magnitude of earthquake occurrence in the region of Arabian Sea during 1932-2002

II) Marine environment in the area of construction: The main factor that is to be considered mainly is the marine environment

in the region of construction. The current of the waves varies from the bottom to the surface due to irregular tides. Maximum

current magnitudes in this area varied from more than 1 m s-1 along the Arabian coast to 10–20 cm s-1 well offshore. The level of

the water rise varies about 2m in the Arabian Sea. This variation n should be taken in to account for construction of tunnel.

Uncertain risks to be avoided and weather forecasting is done to make sure the element is immersed in favorable conditions. July

wind stress in the Arabian Sea is 2-3 times larger than that in January. Arabian Sea currents are highly sensitive to surface wind

stress. Additionally, velocity and direction monitoring is done for better structure. To assess these stresses tests to be conducted

on the models of 1:40 for studying actions of wind, wave and flow.1:60 are done to obtain the tension and heave stress from the

effects of flow and wave. Hydrodynamic parameters were studied by using 1:80 hydro static model tests. These tests were

conducted and design of tunnel is done.

III) Geotechnical conditions: Initially bore hole methods are adopted to find the profile of soil along the tunnel alignment. Since

the construction is to be done in sea the layers comprise of clay, silt and sand. Bore tunnels have been driven from 1970 to assess




the profile of the soil which was started in Hong Kong. Immersed tunnels are to be laid in the trench excavated in the seabed.

During excavation some soils will rebound and after backfilling. So the long term post seismic settlements are considered and

challenges are estimated for correct installment of tunnels and to a proper elevation. Since the dynamic peak acceleration is in

between 0.95 to 1.5 m/s2 the magnitude VIII or magnitudes VII anti seismic standard are followed for design of tunnel.

IV) Settlement issues: Generally, in terms of weight the weight of the tunnel and back fill is less than sub soil replaced. On this

basis one should have more attention on the anti-floating stability of elements, rather than settlements. The major fact is that the

elements often have sufficient anti-floating stability, whereas their settlements are particularly outstanding during construction

phase. Differential settlements are more concerned than absolute settlements. Settlements of tunnels refer to the compression of

subsoil and foundation.it is the compaction of layers and variable loads on the elements that make settlements difficult. The

factors to be considered while measuring settlement is: discontinuity of sub soil, construction in foundation layer, long term

backfill accumulation, fairway excavation, sand liquefaction under earth quake which are majorly taken into account during

settlement factor calculation.

V) Settlement due to offshore conditions (uplift and horizontal problems): The settlements in the offshore conditions is

majorly due to uplift problem and horizontal stability. These two factors are majorly taken into consideration while calculating

settlements in the offshore conditions. It is found in the model tests conducted for previous tunnels and from numerical wave

modeling that the largest wave induces the uplift force on the tunnel for low permeable back fill. In this case the horizontal force

is small which creates some concern on the uplift force might lead to instability of tunnel. Steep gradient of a wave over which

the tunnel with high permeability backfill inside and low permeability outside leads to largest horizontal force larger than uplift

force. So to avoid this 2D hydraulic model tests are to be done for uplift force and finite element models for horizontal stability

problem. The wave conditions are determined by numerical wave modeling with program MIKE21 near shore spectral wave. This

analysis is called bathymetry.

Fig.2 Numerical wave modeling for determination of height of tides

Fig.3 Setup of the 2D hydraulic model tests of the tunnel to determine uplift force

VI) Action of waves: Action of waves on the immersed tunnel is to be considered as a key factor during the construction of

tunnel. The factors that are to be studied regarding action of waves are wave forces, vortex induced vibration a durability.

Morison equation of hydro dynamics is used for the calculation of wave force acting on the tunnel. Boundary line method is also

used to analyses the wave force acting on the tunnel. In order to consider the challenges of wave force with depth layer

integration method is followed. Vortex induced vibration is the action of waves on the tunnel and the combining effect of solid

and liquid forces gives rise to vortex. When the frequency of vortex is close to natural frequency of the structure and components

vibration amplitude may increase. VIV is based on Morison equation, analyzed influence of inclined angle, tension and cable

length in traverse direction. The results showed that: 1) The coupling vibration between cable and tube is obvious 2) The initial

disturbance of tunnel tube has a great influence on instantaneous amplitude of anchor cables. 3) The vortex-induced vibration of

anchor cables can stimulate parametric vibration of system. 4) The stable amplitude of system depends on the size of the vortex-

excited force. 5) The reasonable inclined angle of anchor cables is between 45°~ 60°.the methods to avoid VIV of anchor cables:

1) Choosing reasonable structure parameters. 2) Installing damping devices. 3) Using additional disturbing flow device.

VII) Selection of tunnel cross section: Selection of tunnel cross section effects the immersed and tunnel and also the economy of

tunnel construction. Mostly rectangular tunnel element cross section is used. The arrangement of tunnel element effects the

structure. We have majorly two types of tunnel elements steel immersed tube tunnel and concrete immersed tube tunnel. Concrete




immersed tube tunnel is less economical than steel immersed tube tunnel. The tunnel element may be in the length vary from 180

to 250m and depth of the tunnel vary from 11m to 15m depending upon the conditions in the site of construction A total of 56

elements are to be prefabricated for the construction of tunnel. It is easy to maintain the concrete element than steel element due

to the effect of action of sea water on tunnel. And tests conducted have proved that concrete tube has more durability than steel

tube. So concrete tube element is the best one in constructing immersed tunnel

Fig.4 Pre- stressed reinforced concrete binocular section

Fig.5 Reinforced concrete rectangular section

VIII) Selection of suitable foundation method: We have different types of foundations depending upon the bearing capacity of

the immersed tunnel. The major factor affecting the foundation is the sand between the trench and bottom of the tunnel. The

various methods of laying foundation is screeded bedding, sand jetting method, sand flowing methods and pile foundation. In

screeded bedding the gravel mattress is laid as a foundation using conveyer belts. Sand jetting method involves the pumping of

sand water mixture through nozzles and moving along the tunnel element. Sand flowing method is done by sand positioned above

the unit and flexible delivery pipes are connected on to the sand pipes and sand is pumped under the unit using two adjacent

pipes. In piles method cement is directly injected into the soil and cement columns are made. This method removes the risk of

subsoil settlements. Since this tunnel is of 12km length sand flowing method is used and in hard cases piles methods is suitable

for laying foundation.

4. CONSTRUCTION PROCEDURE

There are set of construction methods for construction of immersed tunnels. The construction of immersed follows certain steps

such as prefabrication of tunnels, installation of tube segments, installation of anchor cables and foundation.

I) Trench dredging and foundation laying: A trench is dredged in the bed of the water channel. This trench which is made

through excavation used for laying foundation to the tunnel elements placed in the water channel. After the completion of

excavation of trench, the next step is laying of foundation. The major factor governing the foundation is the quality of sand

between the excavated trench and the tunnel bottom. Different types of methods have been followed for laying foundations such

as Screeded bedding which involves placing of gravel mattress in the trench and these are compacted well. Sand jetting method

which involves pumping of sand water mixture through nozzles. Once the strip is completed the system moves along the axis of

tunnel unit. Since the construction is underwater deep cement mixed piles (DCMP) are used for foundation.

II) Prefabrication of tunnel segments: The construction of immersed tunnels starts with the manufacturing of tunnel elements in

dock. They are prefabricated in the first stage. The length of each tube is determined by anchor spacing. The internal space should

consist of roadway, escape way, convention channel. Double walled section adopted to make it air tight. The size of the tunnel

must be strictly controlled to meet the needs of underwater construction. The tube should be water proof structure by itself. High

performance fiber reinforced concrete is used to avoid cracks and to control them. The necessary measures are followed to control

the hydration heat of large volume concrete casting. then having the ends sealed with bulkheads.

:




Fig.6 Full face casting form work in casting basin

III) Transportation and installation of tunnel segments: Each tunnel element that is prefabricated in the dock are transported

to the tunnel site usually floating, occasionally on a barge or by using cranes since there are of huge weight. The tunnels that are

transported are then immersed slowly into the sea and make sure that it is above the foundation placed on the trench. After

immersing the tunnel, they are connected by using Gina gaskets which acts as a water proofing agent and prevents the water to

enter the tunnels. The Gina gasket will be compressed and seals up the joints of the two adjacent tunnel units after water between

the bulk heads has been removed. After joining the Omega seal is then clamped across the joint of the inside of the tunnel. This

method of joining is mostly used to increase the design life of tunnel.

Fig.7 Transportation of tunnel elements

IV) Installation of cables: The stability of the tunnel is mainly based on anchors and cables. Since the tunnels are under are

under water and are subjected to the movement of waves they are to be kept rigid with o movement. To do this anchors and cables

are fixed to the tunnel so that there will be no movement in tunnel. The anchors and cables are fixed to the tunnel taking vortex

induced immigration into consideration.

V) Backfilling and Covering the Tunnel: Once a tunnel element has been installed the trench is backfilled with suitable

materials and a protection layer of approximately 1.2 m on top is provided. For the protection layer, rock will be transported from

a quarry, possibly using a barge towed by a tug boat, and, depending on the water depth, either placed by pushing rock over the

side of the pontoon or by grabs mounted on the vessel itself. Within the Natura 2000 area, covering a stretch of approximately 4

km, the tunnel will be lowered a bit further in order to allow for extra backfilling with natural seabed material on top of the

protection layer, so that the natural seabed is quickly re-established.

Fig.8 Backfilling of immersed tunnel

VI) Connections and closure joints: The immersion will take place simultaneously from the coastline the remaining gap

between the last two elements will be closed by means of a steel hull connected to the elements by watertight seals. Inside the hull

reinforced concrete is cast to connect the two sections. The joints between the tunnels are provided with Gina gaskets and omega




seal. The Gina gasket is used to mount on the steel frames of the two adjacent tunnels. After joining the omega seal is clamped

inside the tunnel. These joints will not allow water to enter into the tunnel.

Fig.9 Connections of tunnel elements

VII) Water proofing membrane: Finally, water proofing membrane is used in order to prevent the water seepage and cracks that

may develop in tunnel. This water proofing membrane protects the concrete from surrounding environment. A tunnel is done

waterproofing using steel membranes at the sides and bottom. The top of the tunnel is waterproofed by using SAN-A sheet made

of ethyl vinyl acetate and the edges are covered with epoxy adhesives.in some cases 1.5mm thick PVC membrane is used prior to

steel fixing and attached with PVC ribs on the internal face of the member. On the upper walls acrylic resin membrane of 2mm

thick layer is applied using airless spray techniques.

VIII) Completion Works: When the backfilling around an element has been completed and the protective layer has been placed,

water is pumped out of the ballast tanks inside the tunnel element while ball-last concrete is cast along the full length of the tunnel

floor. Then the ballast tanks and the steel bulkheads separating the tunnel elements are removed and finally the joints between the

elements are completed and the tunnel interior can be finished.

5. ADVANTAGES OF IMMERSED TUNNNELS

Immersed tunnels several advantages over bored tunnels and long span bridges in perspective of cost and time of construction.

Several advantages are as follows:

I. Immersed tunnels have special advantages over bored tunnels for water crossings at some locations since they lie only a short distance below water bed level. Approaches can therefore be relatively short. Compared with high level bridges or

bored tunnels, the overall length of crossing will be shorter.

II. Almost any cross section can be accommodated, making immersed tunnel particular attractive for wide highways and combined road/rail)

III. Immersed tunnels will have less impact on environment (visual, notice) than high level bridges (especially when access to a port is involved air clearances of 60-70 m may be required).

IV. Hydraulic impact and blockage effects become more and more an issue in a lot of places when it comes to the realization of a crossing. Especially in river with large discharges and substantial sediment transport the presence of obstacles in the

river (such as bridge piers) may result in serious sedimentation, resulting in banks or even small islands and the changing

of embankments during periods of high discharge

V. Immersed tunnels can be made to suit most horizontal and vertical alignments. They can be constructed in soils that would preclude bored tunnels or make it very challenging and expensive such as the soft alluvial deposits in large river

estuaries. Immersed tunnel can be designed to deal with seismic conditions.

VI. Bored tunnelling is a continuous process in which any problem in the boring operation threatens to delay the whole project. Immersed tunnel is generally faster to build than a corresponding bored tunnel.

6. CONCLUSION

The development of immersed tunnels and their advantages in suitable topography was discussed and the construction procedure

that is followed in completion of immersed tunnel, different type of cross sections used in immersed tunnel for easy transport of

vehicles and railway ,various new techniques which will improve and increase the efficiency of immersed tunnel when compared

to old construction techniques and the advantages of using these type of immersed tunnel over river and sea crossings when

compared to bridges are clearly discussed. The design of immersed tunnels varies with the conditions of the construction site.

Several studies are to be done for the construction of immersed tunnel with a better design.




7. REFERENCES

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[2] Hamlet Gorsy. -” state-of-art on immersed and floating tunnel technology” Tunneling and Underground Space Technology Vol. 12, No.2 1997

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[6] Endah Wahyuni , Ery Budiman , I Gusti Putu Raka - “Dynamic behaviour of immersed tunnels under seismic loadings and different cable configurations” The journal of Technology and science Vol.23, Number 2, May 2012.

[7] T. Kasper, J.S. Steenfelt, L.M. Pedersen, P.G. Jackson- “Stability of immersed runnel in offshore conditions under deep water wave impact”. Costal Engineering Vol. 55(2008).

[8] Zhi nan Hu, Yong li XIE, Junwang- “Challenges and strategies involved in designing and construction a 6 km immersed tunnel: A case study of HZMB”. Tunneling and Underground Space Technology Vol. 50, 2015

[9] L.C.F. Ingerslev- “Consideration and stragagies behind the design and construction requirements of Istanbul strait immersed tunnel”. Tunnelling and Underground Space Technology,2013

ijrar october 2018, volume 5, issue 4 -issn 2348 1269, p issn … · 2018. 10. 9. · ©e2018 ijrar...

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