Shield tunnelling methods in Japan have been developed so as to cope with very soft grounds such as of alluvial clay or sand. That is to say, segmental joints as well as reinforcing bars are liable to be thickened, and thus shield tunnellings are compelled to use high-price segments. In consequence, proportion of the cost of segmental linings to that of entire tunnelling works attains 30 to 40%.
Tokyo Gas was therefore engaged in developing new type segments from 1992 to reduce the construction cost of this shield construction method. An outline of this development, which may be divided roughly into rationalization of segment structure and retionalization (introduction of tenon segment) of manufacturing method using centrifugal compaction.