CASE STUDY OF THE LONGEST UNDERWATER TUNNEL IN THE WORLD LOCATED IN SOUTH KOREA

1. BUSAN GEOJE FIXED LINK
• Subject : BDD
• Guided by : Shweta Mahajan Mam
• Name : Prajwal Deshmukh

2. INTRODUCTION :-
• The Busan –Geoje Fixed Link project is highly ambitious and
challenging infrastructure scheme to cut down journey time between
korea’s south coast city of Busan and the island of Geoje. With the help
of this project they manage to develop Geoje as tourist spot and save US
$300million by solving traffic related issues with the help ofthis
project. The link consist mainly three parts which are :
8.2 km long link, which includes immersed Tunnel of 48m depth
Athree-pylon cable-stayed bridge
Approach bridges with cable-stayed and road and rock tunnels on
islands

3. BRIDGE COMPONENTS
 Total length : 8.2km
 Lot 1 bridge :1.65 km (1.03 mi)
Between Geoje and Jeoislands, a 1.65 km (1.03 mi) bridge
includes a three-pylon cable-stay bridge. This bridge has two
mainspans of 230 meters (750 ft) with side spans of 106 meters
(348 ft). The pylons are 102 meters (335 ft) tall and there is 36
meters (118 ft) of clearance underneath the bridge.
Lot 2 bridge :1.87 km (1.16 mi)
between Jungjukand Jeoislands includes acable-stayed
bridge with a 475 m(1,558 ft) main span and 220 m(720 ft) side
spans. This bridge provides 52 meters (171 ft) of navigational
clearance and has two 156 m(512 ft) diamond-shapedpylons.
Lot 3 Immersed tube tunnel : 3.2km
The total length of the immersed tunnel is 4 km with two 170
metre long cut and cover sections at both ends.

4. Busan Geoje Fixed link

5.  Bridge :-
• There are five pylons in total for the two cable stayedbridges
which were built in deep sea conditions.
• Caisson foundations have been used for the piers and pylonsas
they eliminate the need for water excluding temporary works.
• The caissons are 33m high precast concrete cellular structures.
• The caisson foundations were fabricated at a casting yard onthe
mainland.
• The heaviest weighs 9,600t but the natural buoyancy of the open-
celled structures was utilised when they were taken out to sea.By
floating them, the weight could be shared between the water and
the crane so a smaller 3,000tfloating crane could beused.

6. DESIGNCONDITIONS:-
 Hydraulicpressure :-
• The deepest foundation point of the tunnel is 47m below meansea
level.
• The water pressure imposes a significant load on the tunnel
elements, in particular in the transverse direction.
• Anumber of other effects add to the water pressure on the tunnel.
The total characteristic pressure can reach an equivalent of 58m
water pressure for certain conditions.
• An increase in the mean sea level of 0.4mhas been included due to
the global warming.
 Wavesandcurrent:-
• Most waves at the project area are generated by winds including tropical
storms and typhoons. Waves generated by distant storms can also reach the
tunnel alignment from southerly directions:
• Anumber of typhoon pass through the project area every year.

7. • The deep water wave height generated by typhoon and swell wavescan
reach 9.2m for a 10,000 year returnperiod.
• Result from the numerical wave modelling show that the significant
wave height is about 0.4mand 0.8mat the most exposed location along
the tunnel alignment.
• Tidal range varies between 0.8mand 1.6m.
• The maximum near surface current spring tide is about0.8m/sec,
reducing with depth to 0.6m/sec at near bottom.
 Earthquake :-
• The Busan metropolitan area is classified as a seismic zone-I based on
the result of seismic hazard analysis as specified in the KoreanStandard
Specification of Highway Bridges.
• Therefore, in this area the corresponding seismic zone coefficient fora
500 year return period is as---
Seismic Zone I
Zone Coefficient 0.11

8. • The risk coefficients representing the ratio of effective peak groundare—
Acceleration coefficient (A) =Seismic ZoneCoefficient × RiskCoefficient
 Shipimpact :-
• The Southern coastline of Korea has a large volume of sea going
traffic including containerships, gas and oil tankers.
• Militarily it is an important and strategic area.
• Overall design of the Busan-Geoje Fixed Link Project considered
loadings from impact and sinking of a 50,000ton vessel sailing to a
neighbouring port.
Return Period(year) 500 1000
Risk Coefficient 1 1.4

9. CONSTRUCTION:-
 Soilimprovement/ foundation :-
• Marine clay is forming the sea bed except in the near shoreareas
where bed rock outcrops.
• The thickness of the marine clay along most of the tunnel
alignment exceeds 20m.
• The major part of marine clay was “very soft to soft” and of“very
high plasticity” to “extremely high plasticity”.
• Tomake the foundation more robust, soil improvement with
cement deep mixing (CDM)and sand compaction piles (SCP) was
chosen.

10. CEMENT DEEP MIXING
(CDM)
• Where the tunnel is placed in a trench ( E3to E14) the clay was
strengthened with walls formed by contiguous columns ofmixed
cement and clay.
• The CDMcolumns were constructed using the wet mixing method,
where cement slurry is mixed with theclay.
• The mixing shafts were first drilled with the rotating blades intothe
soil to the desired depth. The cement slurry is injected in the
withdrawal stage, where the vertical speed of the machine and the
flow rate of the cement slurry were keptconstant.
• Four 1 mdiameter columns with overlaps of 10 cm form a 1.9 m
square column pattern. Toform continuous walls, these square
columns were placed with 10 cm overlaps in rows. The CDMwalls
reach depths of up to 60 mbelow sea level.

12. TYPICAL SCPFOUNDATION LAYOUT AT TUNNEL
ELEMENTS E15 TO E17.

13. Joints
• Inconsideration of the large water depths, the
immersion and segment joints were both
required to have a double water barrier.
• The immersion joint was designed as the
conventional primary Omega seal and
secondary Ginagasket configuration.

14. CONSTRUCTION OF BRIDGE The 29 superstructure spans for the approach bridges are up to90 m long,
weigh up to 2,427 tonnes, composite with a 300-mm-thick concrete deck slab.
 After prefabrication at Obi Bay,the spans were skidded to the waterside for
transport to the site.
 The geology of the site generally comprises marine deposits (sandy andclayey
layers) overlying residual soil (formed by decomposing and weathering of the
bedrock in places) and bedrock. The nature of the bedrock was variable and
consists of Cretaceous mudstones, tuff, sandstones and granite.
 The foundations for the Lot 1 bridge piers were cellular caissons founded on
weak or hard rock, located in up to approximately 30m of water.
 Viaduct and anchor pier shafts were precast concrete, and the three 103-m-
high pylons are cast in situ with the legs providing a signature gentle curvein
transverse elevation. The lower pylon legs taper inward toward the caisson
foundations, reducing the plan area of the foundations.

15. PROJECT
COST
Total cost -1.8 billion
Govt. subsidy- 0.45 billion
By consortium-1.35 billion
lead contractor- Daewoo Engg.& Construction company
• Project has been designed for service life of 100 years.

16. ADVANTAGES:
Economicuseofshape(cross section)
 Verticalclearance
Soil condition:- advantages forasoft soilcondition when a
bridge supportis difficult
 Capableofdealingwithseismic effect

17. REFERENCES
• [1] http://www.roadtraffic-technology.com/projects/busan
• [2] http://www.strukton.com/projects/busan-geoje-fixed-link/
• [3] http://www.industrytap.com/drive-through-the-deepest-immersed-sea-highway/7892
• [4] https://www.youtube.com/watch?v=zKJNZTS1Gco
• [5] www.google.com