An undersea tunnel is a large hybrid structure of steel and concrete formed on the sea bed via the valley filling method. The structures are built at the Sakai Works No. 2 and No. 3 docks. This involves fabrication of the steel shell blocks, assembly, and concrete pouring. For tunnel lengths of 100 meters, three sections can be built simultaneously. The No. 2 dock can accommodate longer tunnel shells of up to 170 meters in length. Hitachi Zosen has built over 40 undersea tunnels including those at the Osakako-Sakishima tunnel, the Osakako-Yumesaki tunnel, the Kobeko-Minatojima tunnel, and on the Nahako-Rinkai road (Port of Naha harbor road) and the Shin-Wakato road immersed tunnel.

Hybrid caissons, which consist of a steel structure and concrete, are often used for bank protection and pier facilities in ports and fishery harbors. In addition to the key role as a breakwater, we are developing a new environmentally sensitive type of caisson that promotes seawater exchange using the energy of waves to restore and preserve the coastal environment as well as slit caissons that have a wave-absorbing effect.

Floating bridges are designed to accommodate tidal movements and are commonly installed at harbors and fishing ports. Hitachi Zosen has constructed over 60 floating bridges, starting with the first steel floating bridge built in the early Showa Era (1926 - 1989).

The jacket method is being adopted in many cases for bridges and bank protection in freight container terminals. It involves the manufacture of jacket superstructures of a steel pipe truss structure on land (i.e., at the factory), which are then carried to the building site and mounted on base piles. The jackets have superior earthquake-proof features and the method is attracting attention as an earthquake-proof-enhancing pier construction method because it can be built on soft ground and in the deep sea. The bridge at the south district pier (-16 m) in North Osaka Port adopted this method and two jackets for it were manufactured at our Sakai Works.

The setting depth steel plate cell method, a construction technique for landfill bank protection, involves hammering steel cylinders called cells (which are produced onsite) into the seabed then filling the cells with earth and sand. This form of protection is superior in terms of its earthquake and waterproofing features, and has been the focus of attention as a suitable construction method for bank protection in the deep sea and for quick construction. Steel plate cells are built on site at the yard from steel materials that are assembled as panels via welding. We have built over 100 steel plate cells to date.

Steel fish reefs are steel frameworks that are placed on the sea bed at fisheries to provide fish with a ready-made breeding habitat. Hitachi Zosen has built over 330 artificial reefs since the first was installed in 1975. The reefs employ a convex shape that is designed to prevent fish nets from becoming entangled.
For maximum quality and minimum construction period, steel fish reefs are assembled as blocks. Hitachi Zosen offers a choice of four models: the HZ-300NB, 400NB, 500NB and 1200NB.