TBM orders for Singapore DTSS Phase 2 14 Jun 2018

TunnelTalk reporting
Fig 1. All 19 TBMs will be Herrenknecht machines, 18 slurry Mixshields and an EPBM
Fig 1. All 19 TBMs will be Herrenknecht machines, 18 slurry Mixshields and an EPBM

All TBMs required for the total 50km of up to 6m i.d. main line sewer tunnelling for the Phase 2 of the Singapore DTSS (deep tunnel sewerage system) are on order with Herrenknecht. The five design-build construction contractorshave all selected Herrenknecht slurry Mixshields and one EPBM for drives through the mixed geology of the Jurong Formation and comprising limestone, sandstone, mudstones overlain by soft waterbearing soils. Confirmation from Herrenknecht Singapore is that all TBMs will be manufactured at Herrenknecht facilities in China for a total 19 TBMs - 18 slurry Mixshields and 1 EPBM (Table 1).

Another Herrenknecht machine to be used by STEC on the T-11 contract is a VSM, vertical shaft sinking machine for the shallower, 12m o.d. diameter shafts on the section of the gravity fed project and closer to the city centre where shaft construction sites within the urban area are limited. As the gravity feed system moves to the west and towards the new Tuas water treatment plant, the system shafts increase in depth and diameter and will be excavated within diaphragm walls.

Table 1. The five design-build contracts of the Phase 2 deep tunnels
Contract T-07 Contract Value: Sing $499 million
Contractor: Ed Zublin AG (Singapore Branch) Length: 12km Designer: Arcadis and Jacobs
From intersection of Jurong Pier Rd and the Ayer Rajah Expressway (AYE) and follow AYE to Tuas Road, plus link sewer Jalan Bahar/ Pan Island Expressway (PIE) junction to Benoi Road/AYE junction
TBM order: Four Herrenknecht Mixshields – 2 x 7.5m o.d. x 3.3km and 3.5km ; 2 x 4.86m o.d. x 2.8km and 2.3km
Contract T-08 Contract Value: Sing $520 million
Contractor: Penta-Ocean /Koh Brothers JV Length: 10km Designer: Arup with OTB Concrete
Main sewer plus industrial water sewer from Jalan Buroh/Pioneer Road and Pioneer Section 1 before passing under Tuas Bay and terminating at Tuas water reclamation plant
TBM order: Four Herrenknecht Mixshields – 1 x 7.36m o.d. x 3km ; 1 x 5.26m o.d. x 2.8km ; 2 x 4.53m o.d. x 2.9km and 2.8km
Contract T-09 Contract Value: Sing $495 million
Contractor: Leighton Contractors (Asia) Length: 8km Designer: COWI with CPG Corporation
From intersection of Clementi Road and AYE to the intersection at Jurong Pier Road and AYE.
TBM order: Three Herrenknecht Mixshields – 3 x 7.51m o.d. x 2.85km, 3.3km, 1.75km
Contract T-10 Contract Value: Sing $340 million
Contractor: Nishimatsu Length: 7.5km Designer: Meinhardt
From intersection of Portsdowns Road and AYE to the intersection of Clementi Road and AYE plus link sewer from Portsdown Road to Leedon Heights and intersection of Clementi Road and AYE to Clementi Road and West Coast Road
TBM order: Two Herrenknecht Mixshields, one EPBM - 1 x 7.41m o.d. x 3km ; 1 x 5.31m o.d. x 3km ; EPBM x 4.78m o.d. x 1.5km
Contract T-11 Contract Value: Sing $472 million
Contractor: STEC - Shanghai Tunnel Engineering Co Length: 11.5km Designer: Surbana Jurong
From Keppel Road to Portsdown Road plus link sewer from Sentosa to Warwick Road
TBM order: Five Herrenknecht Mixshields – 2 x 4.75m o.d. x 3km, 1.6km ; 3 x 4.5m o.d. x 3.8km, 1.5km, 1.5km

A significant part of the works by the design-build contractors and their consultants is design of the specified inner lining that will resist sulphide gas attack and attack by microbiological-influenced corrosion (MIC). For its T-08 contract, the Penta-Ocean /Koh Brothers JV is working with its designer Arup and OTB Concrete on the lining design. The specification is to be met principally with a lining of MIC resistant concrete cast as a second pass lining within the primary segmental lining, and with an HDPE membrane applied as a inner protection of the tunnel structure above the central flow channel.

Contract T-08 also includes two undersea crossings to the planned Tuas treatment plant (Fig 1) as well as nine shafts of 45m to 58m deep. For the undersea tunnel sections, that total a length of 3.5km, an additional waterproof membrane will be installed between the primary segmental lining and the secondary in-situ lining to minimise any water ingress into the tunnel or equally any egress of the sewerage flow when under full operating pressure. These linings are designed to ensure a long-term 100-year design life of the tunnel structures.

For all 20-22 TBMs required by the project to be supplied by Herrenknecht follows other projects around the world where all TBMs required by the different contractors on the project were supplied by Herrenknecht, including Crossrail in London and the Doha Metro in Qatar. In Singapore, the project client, the Singapore National Water Agency PUB, required each competing contractor to name its TBM manufacturer in bid documents and this was carried forward as part of the contract award. Herrenknecht, from its Singapore base, was said to have supported bidders with geotechnical investigations and advice during the procurement phase and with local technical support also available to contractors through the excavation phases. STEC, who might have been expected to procure machines from a Chinese manufacturer, has a close relationship with Herrenknecht and design and manufacture of the DTSS TBMs may include some co-operation.

For the 48km of conveyance tunnels in the north, east and central parts of the island state for DTSS Phase 1, Herrenknecht supplied five of the total eight EPBMs used with the other three supplied one each from Japan by NKK, Kawasaki and Mitsubishi.

In a statement to TunnelTalk, a spokesperson for Herrenknecht said, “it is a great honour to have been able to gain the trust of the contractors with the experience and legacy of thousands of projects worldwide, including in Singapore, and with a high level of support, engineering capability and the will to be dedicated to their projects during the whole project period”.

References

Feedback

Dear TunnelTalk,

It is interesting to read that all 19 TBMs for the DTSS project in Singapore have been selected as a) supplied by Herrenknecht and b) that all but one are slurry machines.

The pros and cons of the first decision have been explored by others and in the TunnelTalk Editor’s Desk comment for this week – however the choice of using all slurry machines is interesting.

Of course, the choice between slurry and EPB depends on many factors – the geology probably being the main one. This has been discussed and explored by many articles and papers over the years. 

Nevertheless, there are many situations where either EPB or slurry can be adopted. This is especially true in the mixed and abrasive ground which can be found in Singapore. In the past, in Singapore, EPB has often been the choice (though admittedly not always). It is a more economical TBM to purchase and does not require the space and expense of a surface slurry treatment plant. 

Often, in benign and straightforward conditions, EPB is without doubt the right choice. However in more demanding conditions of abrasive ground and perhaps greater depth, the slurry TBM option can give more security due to its greater control of face pressure and the reduced wear that it suffers. On the recently completed cable tunnels in Singapore, slurry TBMs were the choice for most, if not all, of the contracts and these were generally completed successfully. Now that slurry has been selected for almost all of the DTSS tunnels, one wonders whether it is the clients and designers in Singapore, or the contractors, that have now come to the conclusion that, in the difficult Singapore geology, the increased investment at the outset in the use of slurry TBMs, giving more security and reliability, saves cost in the long run and is the right choice in difficult and demanding conditions.

Finally it would be interesting to know whether the decision to use all the same type and supplier of TBM was a coincidental one, made independently by all the five different contractors, or whether it was a strategic decision led by the client, while, without doubt, leaving the responsibility for the machines with the contractor.

With regards,
Richard Lewis, YL Associates Limited, Hong Kong

           

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