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There were a number of concrete structures built on the Te Maire Street Stormwater job. Two important projects of note were: • The BST duct. • The Pipeline C collection manhole.
The BST duct was a 13m x 4m x 0.75m service duct covered with 80mm thick steel plates. The duct was designed to carry chemical and fuel pipelines across Quay Street.
The duct was designed as a bridge so that loads would not be transferred to the three DN1800 pipelines the soffits of which were 300mm below the bottom of the duct.
The duct had to withstand loads of 120 tonnes from fully loaded log loaders. The duct was pre-cast in two 6.5m sections and then stitched together onsite.
The duct was lifted into place with two 170 tonne cranes performing a tandem lift. The concrete was a mix >50MPa in strength and most of the reinforcing steel was HD25.
The Pipeline C collection manhole was a 3.5m x 3.5m x 3.5m concrete structure with 400mm thick walls, floor and roof.
The purpose of the manhole was to collect five pipes of various sizes from DN300 to DN1200 and send them out a DN1800 outlet pipe.
The manhole also needed to be designed to withstand loads of 120 tonne. The floor and two walls were pre-cast off site, while the roof and other two walls were cast onsite.
The manhole was constructed mainly from HD20 steel and a 50 MPa concrete.