PROJECT | CROSS RIVER RAIL


Right:


Cross River Rail vertical alignment


Cross River Rail’s 5.9km of twin tunnels will stretch


from the project’s southern portal at Dutton Park, under the Brisbane River and CBD to the northern portal in Normanby. The parallel twin tunnels are segment lined, with cross passages every 240m. At their deepest, at Kangaroo Point, they are 58m below the surface.


The two TBMs are working in parallel, excavating from


Woolloongabba north to Normanby. The remaining, short 870m section of tunnel from Woolloongabba south to Boggo Road is being excavated by roadheaders. Cross passages are being mined by excavators, rock


hammers, and drill and blast; the latter is the preferred method within the TBM tunnels as it reduces overall construction time. Where blasting is not deemed feasible, manual excavation with a rock hammer is the fallback. Each cross passage is approximately 5.8m wide, 5.8m high and 6m long. Sixteen of them are permanent to act as emergency access or escape points; additional temporary cross passages facilitate in-tunnel access during construction. The TBMs launched from a shaft at the


Woolloongabba site: Else launched in February 2021, Merle a month later. They are twin-shield machines supplied by Herrenknecht, 7.23m in diameter. The tunnel intrados is 6.37m diameter – the extrados is 6.91m – and the precast lining segments are 0.27m thick. They are rebar reinforced and six to a ring including two shorter keystones. “Further out from the city centre the roadheaders are


encountering conglomerate and siltstone/sandstone in their tunnels,” says Luong, “but the TBMs are working through Brisbane’s notoriously hard Neranleigh-Fernvale rock beds and Brisbane tuff rock. Given that situation, no hyperbaric interventions are needed, and no hyperbaric chambers are installed on the TBMs. Over 240 boreholes along the tunnel alignment have given us a full geotechnical model.” The 25,000 concrete lining segments are produced


by Wagners off-site, at their plant in Wacol, around 17km from Woolloongabba. They are producing 500- 600 segments per day, initially on a day shift only but moving to day and night shifts as the project gets into its stride, and delivering them by truck, 40 trucks each night, to a holding yard at the Gabba where they are loaded by forklift onto MSV to delivery to the TBMs. They are edge-lined with waterproof gaskets and connected with dowels and speedbolts.


38 | November 2021


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