Naha tunnel extends approximately 1.1 km across Naha harbor channel, and is part of an expressway. The tunnel is constructed with eight prefabricated steel-shell sections submerged at the site. The No.2 shell section fabricated at our factory was delivered to the site in March 2002. This paper reports the new technologies applied to the construction and transport of the shell section.

1) All members of the shell were constructed with a fully sandwiched structure, that is, double steel shells filled with concrete in-between.

2) The shell section was loaded on a barge using skid bases. To reduce the friction during loading the section, the shell skid beams were coated with stainless steel at the bottom, and the top of the skid supports was coated with Teflon.

3) The semi-submergible barge loaded with the section was towed to Naha, Okinawa.

4) After the section was tied up at a quay near the site, super-politicized concrete was placed into space between the shell plates while the shell was floated.

5) The three-dimensional measurement was implemented on a regular basis for the whole shell section to check for any irregularity or deformation.