Long Pipejack in New ZealandA 55-tonne Herrenknecht AVND 1800 microtunnelling machine, painted in Canterbury colours and nicknamed 'Dora the Bora', completed the first underground stretch of the NZD87 million Ocean outfall sewerage project in Christchurch on 31st August, 2007. Work on the first tunnel section started in April and Dora emerged in the exact spot calculated at the oxidation ponds, completing the 871 m-long tunnel under the Avon-Heathcote estuary from South New Brighton Park in a single push without interjacks. This is believed to be the longest pipejack microtunnel in New Zealand-Australasia-Southern hemisphere.The tunnel is built by McConnell Dowell Constructors. To avoid machine stops for any length of time because the earth cools and closes around the pipe, making it difficult to get it moving again, the number of shifts was increased. In early August, work had to stop for three days while a seal was reinforced. When it came time to get the boring machine moving again, it took 600 tonnes of pressure, nearly the maximum amount of power the hydraulic ram can muster, to get it shifting forward. The contractor installed about six sections of pipe a day. Each section of pipe is three metres long. Tunnelling operated 24 hours a day, seven days a week. Visit www.ccc.govt.nz/oceanoutfall, www.macdow.com.au or www.mcconnelldowell.com and www.herrenknecht.com Dora the Bora, the Herrenknecht AVND 1800 microtunnelling machine The machine's small pilot cabin with its pressure gauges, computer screen and panel of illuminated buttons is located amid pine trees of South New Brighton Park. The microtunnelling machine is remote controlled by pressing a button, which sends a signal along a wire trailing from the cabin across the sandy ground, down into a 14 m-wide, 12 m-deep circular pit and into a concrete tunnel opening at the base. The message then travels along the circular tunnel - big enough for a 1.80 m-tall person to walk along keeping his/her head down - until it reaches the small boring machine. The machine receives the message and powers down. The borer is not self-propelled. Instead it is pushed through the sands from behind by 300 tonnes of pressure from a hydraulic ram sitting at the bottom of the circular pit.When tunnelling began, the borer was pushed horizontally into the earth and a 3 m length of concrete pipe placed behind it. The hydraulic ram slowly pushed the piece of pipe and the machine into the earth before placing a new piece of pipe behind it. This process has been repeated until the micro TBM emerged from the reception pit nearly 900 metres away in Bromley with the length of connected concrete pipes filling the tunnel behind it. The machine scoured its way through the earth at a rate of 14 centimetres a minute.Now that Dora has completed the first mission, it will be lifted out of a shaft that has been excavated in preparation for the arrival of the tunnelling machine and returned to the one in South New Brighton Park to begin the second tunnel toward the sand dunes. The third tunnelling mission will take Dora from the dunes to just beyond the surf zone at New Brighton beach. Once the 2.3 km concrete tunnel emerges from the sloping seabed sand beyond the surf zone, it will connect to 360 m-long plastic pipes sunk to the bottom of the sea at Diamond Harbour to continue its journey 3 km out to sea. The plastic piping is now being put together in Lyttelton docks. When they are needed they will be refloated and towed around to Southshore beach before being sunk into place.When the project is completed at the end of 2008, a pipeline will run 5 km under the ground in a straight line from the oxidation ponds in Bromley to a point 3 km out to sea passing beneath the Avon-Heathcote estuary, South New Brighton Park, Jellicoe Street, the dunes and the beach. The pipeline will carry treated sewage out to sea, replacing the current system that releases the untreated water from the oxidation ponds into the estuary at high tide. 39/07.