TBM orders for Singapore DTSS Phase 2 14 Jun 2018

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.

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”.