Deep Tunnel Sewerage System, Upper Thomson Link Sewers, Singapore

Construction of 32 shafts down to 40 m deep as well as 5 km of sewers ranging between 400 mm and 2400 mm internal diameter done by pipe jacking method. Reinforced concrete jacking pipes with HDPE inliner. Pipe design, production and supply.
The temporary shafts were constructed by caisson sinking method with a maximum depth of 40 m. The diameters ranged from 4.4 to 8.8 m. The temporary jacking and receiving shafts consisted of circular concrete rings. The rings were formed by segments which were tied together with rods.
Depending on the often changing soil and groundwater conditions, the 12.5 m long pipe jacking machine (TBM) with an outer diameter of 2,890 mm was equipped with a specifically designed cutting wheel with interchangeable tools to handle the different ground conditions, operated in two different modes - EPB and Slurry.

The main concept of this design is that the machine can be operated in EPB mode in soft ground conditions and when it faces rock it will be switched to operate as a slurry machine.
The longest drive for the ID 2400 mm sewer was 515 m long using 3 numbers of intermediate jacking stations.
Difficulties: The ground conditions changed very frequently and abruptly. A highly permeable interface zone was encountered with ground water pressures up to 3 bars.
Geological Conditions: The conditions on site varied from hard fresh granite to soft marine clay.
The contract was completed 8 months ahead of schedule.
Winner of the BCA Construction Excellence Award 2007.