The TBM’s slurry system is a water based system drawing water directly from the river. A bentonite slurry was needed to start through the fill material but there was sufficient natural clay in the glacial deposits under the river. The separation plant, supplied by Schauenburg and Bird Humboldt of Germany, is working well and is handling some 2500m³ of slurry/h. To circulate the slurry, two high performance 950kW variable-speed Warman slurry pumps from Australia are used on the discharge pipeline – one on the TBM and another at the low point of the tunnel to maintain the outbound velocity – and there are two Habergamm pumps from Germany in the separation plant feeding cleaned slurry back to the TBM.
The pressurised slurry is working well to support the face of mixed materials and reacting swiftly to balance the variable pressures across the 160m² face. The slurry support system has also controlled settlement over the wide settlement trough to a maximum 10mm. Settlement under a residential area on the north land fall of the tunnel and under a cover of only 12m is minimal.
