Definition - What does Casting Basin mean?
A casting basin is a large area of land, surrounded by berms, which is capable of retaining water. It is a designated area often used for the construction of tunnels crossing rivers where elements for immersed tunnels can be fabricated in dry conditions and then flooded to allow the elements to be floated out and taken away.
Trenchlesspedia explains Casting Basin
Once completed, tunnel elements are sealed and tested to ensure against water ingress. The casting basin is then filled with water, joined to the adjacent river and tunnel elements are moved into place under the water's surface. The casting basin is used for the casting of concrete tunnel sections. It's oriented at right angles to the river to be crossed to facilitate the movement and placement of large tunnel segments using the immersed tube tunneling technique.