Final tunnel awards on giant STEP project Jan 2012
Peter Kenyon and Shani Wallis, TunnelTalk
The last two link tunnel contracts on Abu Dhabi's US$1.7 billion Strategic Tunnel Enhancement Programme (STEP) are awarded to Strabag subsidiary Ed. Züblin AG.
The US$385 million award is for 50km of 200mm to 3.1m diameter link sewers and their drop shafts for contracts LS-01 and LS-02, to connect new and existing sewer lines to the main deep tunnel trunk main that is currently under construction in three lots.

40km of main sewer tunnelling is split into three contracts (left) with 50km of linking sewers completing the network (right)

Diana Neumuller-Klein of Strabag confirmed that the LS-01 contract involves construction of a 35.7km network beneath the central business district of Abu Dhabi Island. She said: "Tunnel diameters will range between 200mm and 2.8m, with 247 manhole shafts to a depth of between 8m and 26m. Contract LS-02 is located on the Abu Dhabi mainland and involves construction of a further 15.4km of link sewers with diameters ranging between 200mm and 3.1m, plus a further 95 shafts."

Impregilo lowers one of five EPBMs it is using to complete its two of the three main lots

Klein added: "Pipe jacking is to be used for construction of the tunnels and the overall construction period for both packages will be 39 months. The projects will be jointly executed by the Pipe Jacking Division of Züblin Singapore and Züblin’s Abu Dhabi branch."
Austrian-based Strabag acquired control of Züblin in 2005 when it bought an additional 48.7% share of the business from previous owner Bayerische Landesbank. At the time it already owned a 5% stake in Germany's fifth largest construction group.
The STEP project for the Abu Dhabi Sewerage Services Company (ADSSC) is being managed and designed by USA-based consulting engineer CH2M-Hill. The project comprises a 41km-long TBM-bored gravity tunnel with diameters of 4m-7m plus the additional 50km of link tunnels and more than 300 drop shafts.
Project scope also features a new $572 million pumping station that will lift flow from the main tunnel to the adjacent and newly completed wastewater treatment plant at Al-Wathba. The pumping station SP-01 contract was awarded to Odebrecht of Brazil in December 2010 and notice to proceed for the pumping station and link sewers contracts is scheduled for March 2012.
Table 1. Details of Abu Dhabi's main STEP contracts
Contract Company Value (US$m) Tunnel length Tunnel diameter TBMs
T-01 Main tunnel Samsung $270 15.5km 4m 3
T-02 Main tunnel Impregilo $243 15km 6.3m 3
T-03 Main tunnel Impregilo $200 10.5km 7m 2
LS-01/LS-02 Link tunnels Züblin $385 50km 200mm-3.1m
Pump Station Odebrecht $572 n/a n/a n/a
Impregilo of Italy is currently constructing the 25km length of the main tunnel under Lots T-02 and T-03 for a total value of $443 million. Lot T-01, for 15km of 4m-diameter tunnelling, was awarded to Samsung of Korea. Samsung is using three machines manufactured by Kawasaki in Japan. Impregilo will operate five Herrenknecht EPBMs for its two contracts.
Impregilo's Lot T-03 contract comprises a 10.5km tunnel to connect the existing Mafraq Pumping Station to the new Al-Wathba Pump Station and involves the use of two 7m-diameter EPBMs for pressures up to 8bar. The scope also includes four access shafts to depths of between 60m-80m.
Lot T-02 sees Impregilo using three EPBMs to complete 15.2km of boring at between 40m-50m deep, and involves excavation of six further access shafts. These three machines mobilized in 2011 and by the end of last week (13 January, 2012) they had completed 8,660m of their total 15,250m drives and are on course to hole out in April and May of this year.
The first of two TBMs from Impregilo's T-03 contract is on site and scheduled to be lowered into the launch shaft this weekend (21 January, 2012) and the second is en route from Herrenknecht's factory in Germany.

51km of link sewers connect to the 41km-long gravity flow main tunnel

On Samsung's T-01 contract the first two machines are being delivered while the third is to be factory tested next month (February 2012) before it too will be shipped from Kawasaki's factory in Kobe.
A report today from Abu Dhabi confirms that all eight TBMs are likely to be running at the same time. A source told TunnelTalk that as work on the T-02 contract was winding down, excavation on T-01 will be starting up. With the link sewers having the longest construction period, completion of the entire system is scheduled for July 2015.
The main gravity tunnel and its associated link sewers will enable ADSSC to eventually decommission 39 existing pumping stations and significantly reduce operating and maintenance costs.
The population of Abu Dhabi is expected to double over the next decade. The new elements of the STEP project will more than triple ADSCC's current wastewater capacity of 450,000m3 /day to 1.7 million m3, enough to meet the Emirate's needs until at least 2030.
Abu Dhabi, which records an average annual rainfall of just 1cm, is the third largest per capita water consumer in the world at 550 litres/person. Its existing wastewater treatment capacity is already running at 150%. Some of the grey water collected by the system will be used for irrigation.

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