STRATEGIC TUNNEL
ENHANCEMENT PROGRAMME
(STEP)
Presented By
MD.MANNA
N
2005A0105
CONTENTS
INTRODUCTION
PROJECT DETAILS
NECESSITY
MAIN FEATURES
GEOLOGY
TUNNEL CONSTRUCTION
PUMP HOUSE CONSTRUCTION
CHALLENGES
REFERENCES
CONCLUSION
INTRODUCTION
It is a Deep gravity Driven Underground sewerage
system Designed to collect Waste water Flow of 1.9
million cubic meters a day From Abu Dhabi city.
Transports Sewage through tunnels to Treatment plant
Situated at 40 km away from the City in Arabian Desert.
One of the Largest Tunnel Sewerage Systems in the
World.
Comprising of Main Tunnel Sewer and Several Branch
Sewers
Project Details
Project Type : Hydraulic Waste water network Tunnel
Owner : Abu Dhabi Sewerage Services Company
(ADSSC)
Investment : 1.6 billion USD
Capacity : 1.9 M m3/day
Design Period : 100 years
Year of commencement : 2009
Year of completion : 2014
Managing Company : CH2M HILL
Necessity
Due to Rapid Urbanization Old Sewage treatment unit was
facing issues
Sewers were running full and causing operational Problems.
Old Treatment plant Built in 1980’s was Originally Designed to
treat 2,60,000 m3/day.
At that time city Was Producing 6,00,000 cubic meters of
Sewage every day Causing Overflow at Manholes and other
sewer appurtenances.
ADSSC Thought to expand the existing sewer system
Right beneath the city streets which will Accommodate entire
sewage into a giant Super Tunnel.
Sewage Overflow Old Treatment Plant
MAIN FEATURES
“STEP” consists of Mainly 3 Components
i. Main Tunnel Sewer
ii. Branch Sewers
iii. Deep Pumping Station
Geology
During the excavation of the Working Shafts several samples of
ground were collected.
The samples show the main composition of the ground area:
- light grey gypsum with some cracks.
- light grey to dark grey mudstone intercalated with gypsum.
MAIN TUNNEL
Constructed using Pipe Jacking Method
Diameter : 5.5m , Length : 41 km
It Begins at a depth of 25 m beneath the city and It is aligned
at a slope that allows system to work solely on gravity
Removing the need for other Pumping Stations thus saving
energy and money.
The government will be able to Eliminate 35 Existing Pump
Stations Through Gravity Method
It is designed to last for 100 Years.
Depth of the Shafts will increase from city center to Pumping
station Where it reaches to 100 m
The tunnel Length is divided into Three Parts named T-01,
T-02 & T-03
Tunnel was constructed
Using Precast concrete
segments transported
From factory .
Lining on Tunnel surface
As sewage will produce Vapours of sulphuric acid at high
temperatures ,concrete lining was Necessary.
Lining was done using HDPE Sheets ,square shape With Studs
on one side For fixing on to the surface.
Lining material was designed for a life span of 80 years .
Lining was provided in 8 Different colors at Different sections
It will help in Fixing the Patches if concrete gets Eroded and
lining material falls.
ADSSC workers can directly identify and Repair patches by
Sending Remotely handled vehicles Through Access Shafts.
Branch sewers
Consists o f diameters
Ranging
from 200 mm to 2 m
Connecting
The main Sewer from
different locations.
Including around 300
shafts.
Length of Branch sewers is
about 43 km.
Access Shaft at site
Machinery Used
Tunnel Boring
Machines (TBM) :
Total 8 TBM Were
employed
Each TBM Ranges b/w
80 to 100m long
They were Taken in
parts to the Special
Operation Hole and
Assembled underground
TBM
OPERATION OF TBM
There is a cutter Head Fitted at Front of TBM Which is a
Rotating Wheel covered with Disk cutters which will cu the
Rock mass.
The Steel ring Behind the TBM Will prevent the hollowed
Earth From collapsing
A Robotic hoist positions the Concrete segments to form a
Tunnel ring.
Once Each ring is complete Hydraulic Arms push the TBM
Forward into the Rock
If conditions are perfect Machines will up to 100m in a
week.
PUMPING STATION
Situated in the Desert, it is end of the Major Tunnel
It is of depth 100 m and 50 m in Diameter
It Replaced Existing 35 small Pump Stations of city.
Pumps and Motors were Imported from Japan
Total 8 motors were Employed Each of Capacity 6300 volts &
Pumping capacity of 5000 lit/sec
It was deepest Underground Pumping station at that time.
It was Decided by Engineers to Build a “Diaphragm Wall”
which will arrest the seepage of Ground water to carry out
Excavation .
Pumping Station Shaft Construction
DIAPHRAGM WALL :
Made up of 26 Concrete Panels Each of 40 m Depth .
For every Panel 720 Tonnes of concrete was Required.
Panels will create a Water proof barrier .
TOE BEAM :
A circular Brace called Toe Beam Was Introduced at Base of Wall to
prevent it from collapsing.
To Build The 40 m Wall a 40m Trench Was Excavated
Pumpable mud Was poured to support the Excavation .
Reinforcement in the form of cages was placed and concreting was done.
Section Showing Diaphragm wall with Toe Beam
Material Transportation
A Train Was Operating in Tunnel Which Was
supplying Materials, Manpower, Grout to the
Machine.
A High Tech conveyor Belt System was Used to Move
the Dug Material by Pouring into Wagons.
And Wagons are lifted by Large cranes and Rock mass
was Deposited out side.
CHALLENGES
High Temperature :
Concreting When temperature was 500 Celsius Was a
Difficult Task . Temperature of 240 Celsius For Concrete
Had To be Maintained To avoid Cracks.
Engineers Replaced some Part of Water with Ice To
Decrease the Overall Temperature of Concrete.
Break Down of Conveyor Belt
The Last Curve of the Drive was Approaching.
The Functioning Of TBM Was Halted.
The next Day Conveyor Belt was repaired Successfully.
Water Leakage From Diaphragm Panel
The rate of Leakage was 1000 lit/day
To stop this Breach was Reinforced and Connected with
Panel Edges and Concreting Was Done.
Originally Excavation was Planned to 8 m per week But
it Reduced to 2 m per week due to Repair.
One week work was Halted.
Repair of Breach
To Tackle This situation
Engineers Made Modification
To the Original Plan.
Instead of Constructing Toe
Beam at 40 m Depth, It was
Lifted up and Placed at a Depth
of 30 m.
With This Excavation was
Taken up without any
Problems.
Segment with Crack
Tunneling Was Completed in October 2013. TBM were Safely
lifted in Parts Using Cranes and Transported.
Tunnel End Point at Pumping Station
Shaft at Pumping Station
CONCLUSION
“STEP” has The Potential to Satisfy the Growing Demand of
Management of Sewage coming from Present and Future
development Foreseen of the city.
ADSSC has been Successful in Providing a Sustainable
Sewerage Solution.
But if Rapid Population increase Takes Place There might
be chances of Sewerage System Reaching its Full
capacity Prior to its Design Period.
REFERENCES
NGC Abu Dhabi :
Mega Structures – Abu Dhabi Super Tunnel
https://www.youtube.com/watch?v=TKgrD-1EbHM
Flingbat's visualization studio
https://www.youtube.com/watch?
v=RQvvRKCJ_Ig&list=PLJ0dzMoJQ M3MEYuZbrboLvDmumESn-
0Hj&index=9
Ground conditioning: STEP Abu Dhabi sewer project
(1)MAPEI, Underground Technology Team, Milan,Italy
(2)IMPREGILO, Abu Dhabi, UAE .
