Immersed tube method for underwater crossing includes the following basic construction steps:
(i) Prefabricating long tunnel units (concrete orsteel shell) in a dry-dock or shipyard
(ii) Floating and towing the units with removable bulkhead to site
(iii)Immerse the units in a pre-dredged trench
(iv)Connect the units one by one
(v) Covering completed tunnel with backfill
Steel immersed tunnel is a number of times adopted due to the ease of fabrication and its relative lightness. Furthermore shorter construction time is essential when compared with concrete immersed tubes.